# Catnip immunity and alternatives

Frequency of cat reactions to catnip and catnip substitutes (statistics, psychology, meta-analysis)
created: 7 Nov 2015; modified: 08 Mar 2017; status: in progress; confidence: likely;

Not all cats respond to the catnip stimulant; the rate of responders is generally estimated at ~70% of cats. A meta-analysis of catnip response experiments since the 1940s indicates the true value is ~62%. The low quality of studies and the reporting of their data makes examination of possible moderators like age and gender difficult, but one possible moderator is that Japanese cats may have a response rate closer to 90%. Catnip responses have been recorded for a number of species both inside and outside the Felidae family; of them, there is evidence for a catnip response in the Felidae, and, more uncertainly, the Paradoxurinae, and Herpestinae.

Catnip is a plant which causes stimulated and excitable behavior in many domestic cats, which is fun to play with. It is the best known of at least a dozen plants with psychoactive effects on cats, and far more popular, cheaper, and easily purchased than alternatives like Tatarian honeysuckle, silvervine, or cat thyme. However, a large fraction of cats do not respond (non-response may be a genetic trait given Todd 1962’s pedigree chart) but may respond to one of the alternatives. For example, of my family’s two cats, neither responds to catnip but one responds to valerian, one to honeysuckle, and both to silvervine.

This raises several questions:

1. what fraction of cats, exactly, are catnip-immune?
2. how often do the catnip alternatives work?
3. does immunity to one alternative predict immunity to others?
4. since some alternatives can be hard to find and expensive, what is the optimal order of alternatives a cat owner should try to find one that works?

# Population frequency of catnip response

## Literature review

Catnip is frequently discussed in the popular & secondary literature without citation, and after tracking down claims, the primary literature on catnip effects & response is relatively small1; for a good overview, see Tucker & Tucker 1987

• tested extracted nepetalactone and caryophyllene on 10 lions of unspecified but mixed genders/ages; the 7 adults all responded to the nepetalactone and not the caryophyllene (the 3 cubs responded to nothing).
• 14 responders, 12 non-responders in a Siamese breeding colony so 46% immunity rate in this sample. (8 male responders, 6 female responders, 2 male non-responders, 10 female non-responders.) Todd also surveyed cats in local pounds and animal hospitals, finding 26 of 84 sampled were non-responders or a ~31% immunity. Todd considers the genetic pattern most consistent with a fairly common genetic variant which is autosomal dominant.
• Todd 1963, The catnip response

• In surveying the 26 breeding colony & 84 local cats, Todd found no large correlations with sex, breed type (Manx/Siamese/tabby/Agouti), white spotting, blue dilution, polydactyly, long hair, or castration. (32 male responders, 11 male non-responders, 26 female responders, 15 female non-responders.) Except the usual observation that young kittens rarely display a catnip response: of 39 under 12 weeks of age, 4 responded.
• Cross-species results:

1. Viverrids (pg42/73), unspecified gender/age/species:

Table 3. Results of testing Viverrids with catnip. Figure in parentheses indicates number of individuals tested. + = positive, ?+ = possibly positive, ?- = probably negative, - = negative, I = indeterminate, animal would not or did not investigate leaves.
Sub-families Genera N + ?+ ?- - I
Viverrinae Genetta 3 0 0 0 2 1
Viverrinae Viverra 1 0 0 1 0 0
Viverrinae Civettictis 2 0 0 0 1 1
Paradoxurinae Nandinia 5 0 0 3 2 0
Paradoxurinae Paguma 2 0 0 1 0 1
Paradoxurinae Arctictis 3 1 1 0 0 1
Herpestinae Herpestes 1 0 0 0 1 0
Herpestinae Atilax 3 0 1 1 1 0
Herpestinae Ichneumia 1 0 0 0 0 1
Cryptoproctinae Cryptoprocta 1 0 0 1 0 0
2. Hyenas (Hyenidae): 0/3 responders of 2 males/1 female (pg41/72), unspecified age, genus, or species, presumably either spotted or striped hyenas.
3. Felidae: (pg42/74). Todd’s table and results have been summarized as thus by Tucker & Tucker:

Within the subfamily Pantherinae of the Felidae, Todd (1963) found the typical catnip response in 16 lions (Panthera leo) (14 positive responders, 2 negative responders), 23 tigers (Panthera tigris) (8 incomplete responders, 13 negative responders, 2 inconclusive responders), 18 leopards (Panthera pardus) (14 positive responders, 4 negative responders), 8 jaguars (Panthera onca) (7 positive responders, 1 negative responder), 4 snow leopards (Panthera uncia) (4 positive responders), and 1 clouded leopard (Neofelis [Panthera] nebulosa). Within the subfamily Acynonychinae of the Felidae, he found that 3 cheetahs (Acinonyx jubatus) did not respond to catnip. Within the subfamily Felinae of the Felidae, he found the typical catnip response in the 2 bobcats (Felis [Lynx] rufus) (1 positive responder, 1 negative responder), 1 European lynx (Felis [Lynx] lynx), 5 pumas (Felis [Puma] concolor) (2 positive responders, 2 negative responders, 1 inconclusive responder), 1 Asiatic golden cat (Felis [Profelis] temmincki), 5 ocelots (Felis [Leopardus] pardalis) (4 positive responders, 1 negative responder), and 6 margay cats (Felis [Leopardus] wiedii) (4 positive responders, 2 negative responders); no catnip response was observed in 2 servals (Felis [Leptailurus] serval), 1 swamp cat or jungle cat (Felis chaus), 1 Pallas’ cat (Felis [Octocolobus] manul), 1 leopard cat (Felis [Prionailurus] bengalensis), 1 African golden cat (Felis [Profelis] aurata), 2 fishing cats (Felis [Prionailurus] viverrina), 4 jaguarundis (Felis [Herpailurus] yagouaroundi), and 1 pampas cat (Felis [Lynchailurus] pajeros).

The summary of Todd’s Felidae results is correct but omits that Todd also used a questionnaire to estimate 4 responders & 13 non-responders among the ocelots in addition to his personal testing of the 5 ocelots but Todd notes he has reservations about the validity of the data gathered by this method (possibly because the response frequency 4/17 is so different from his personal 4/5 response frequency) so that data is probably best excluded. Todd also mentions a report of a ligeress (female hybrid of a male lion & tigress) from de Bary of the Utah Hogle Zoological Garden who is a catnip non-responder. For the meta-analysis, I code the questionable positive/negative responses as confirmed responses. Sex is usually unspecified, but individual-level data is provided on the lions, tigers, & leopards. I excluded the pampas cat and additional questionnaire data in line with Todd’s notes that the data were highly unreliable.
• Bates & Siegel 1963, Terpenoids. Cis-trans- and trans-cis- nepetalactones

They chemically separated the two isomers; the extracted isomer I was mostly inactive when presented to 8 cats with just 1 more interested in I than II (though they caution there might still have been contaminating II in the I extract), but three were strongly attracted and two showed slight preference for isomer II (_trans-cis-_nepetalactone), so arguably 5 out of 8 were responders. (Breed and sexes unspecified.)
• Palen & Goddard 1966, Catnip and oestrous behavior in the cat

Reactions: 23 responders, 20 non-responders, so 47% immunity rate. (37 male, 28 female, mixed breeds: 6 male responders, 6 male non-responders, 9 castrated male responders, 5 castrated male non-responders, 5 female responders, 5 female non-responders, 3 spayed female responders, 4 spayed female non-responders.)
• Hayashi 1968a, Pseudo-Affective Reflexes of Cats produced by Extracts from the Plant Actinidia polygama claims to have found no responses in an unspecified but probably >4 number of cats (as he used young and old cats of both sexes) when testing nepetalactone (catnip) and actinidine solutions, aside from two actinidine reactions
• A 1966 conference talk published in the 1968 proceedings, Hayashi 1968 is light on details. Tucker & Tucker summarize it as Hayashi (1968), who tested a wide range of animals (dogs, rabbits, mice, rats, guinea pigs, fowls, and cats) with powders of Actinidia polygama and N. cataria, found that the catnip response is induced in cats alone., which tells one about as much as the original report does:

…actinidine (1) and catnip…have always been the source of much interest…When powder of these plants was presented to cats, they displayed a peculiar behavior…The reflex behavior is induced by the smell, not by taste and not via the circulation. The cat must be tamed by the experimenters and must be adult: male or female are quite the same…Once I tried with English cats in London, and with American cats in New York, each time taking advantage of visiting my friend’s laboratories, but English as well as American cats were rather cold…We tried experiments with dogs, rabbits, mice, rats, guinea pigs and also with fowls but they had no such reflexes to the plant powder…From these results, we presume that the reflex ability is restricted to cats and feline species in vertebrates, and its reflex centre would be situated in the subcortical, presumably limbic, structures…That the phenomenon is restricted to the cat family is said also in Japan.

• Q [J.W. Johnson Jr]: This is a simple question that might be relevant to your point, Doctor. In Northern Virginia, where I live, there are stands or clumps of catnip. I’m not aware of house cats visiting the catnip stands while in the living state. Do you know whether this has been reported.
• A [T. Hayashi]: No, I don’t think so. We have natural growths of bushes of actidinia polygama in several parts of Japan, but nobody noticed that these bushes attracted cats from the villages….In the central part of Japan we have many actidinia distributed from north to south. But I have not heard that cats gather in the stands of the plant. Maybe the drying of the plants or burning of them is the most effective.
From this I gather that Hayashi must have tested at least 2 cats in the USA, 2 in the UK, and 2 in Japan (because he always uses the plural cats, and he compares the US/UK cats to Japanese cats). Hayashi 1968a implies >=4 cats were used but not their national distribution. To be conservative in lieu of more precise data, one would have to code the Hayashi data as 2 cats per country. He does mention that the USA/UK cats were rather cold, which implies an intermediate but existent response much less than the Japanese cats. (It is also intriguing given Sakurai et al 1988’s later possible implication that 16 of 16 cats in Japan reacted to catnip but not foreign breeds.) If we assume the n of each group of cats is 2, then the response rate must be 1/1/2 respectively, as otherwise Hayashi would either have described it as no response like the other species or as the same response as the Japanese cats. The other species are also pluralized, so at least 2 of each, and all responses must have all been 0 responders since they had no such reflexes and it is restricted to cats and feline species. Specific species (presumably the other animals are either domestic or lab species), sexes, breeds, and ages are not given.
• In a metabolic study, purified nepetalactone was force-fed to 6 cats in gel capsules; as expected due to the olfactory requirement (previously demonstrated by Todd with surgical manipulations of olfaction), none of the cats exhibited the catnip response and the result is irrelevant.
• Tested 17 cats initially; 14 responders. (Mixed breed, both genders; breakdowns of response not given.)
• Hill et al 1976, Species-characteristic Responses to Catnip by Undomesticated Felids; Tucker & Tucker summary (apparently based on counting the descriptions in Table 3 or Table 4):

Hill et al. (1976) found that lions (5 positive responders, 6 partial responders, 1 negative responder) and jaguars (3 positive responders) are extremely sensitive to catnip, while tigers (5 negative responders), pumas (4 negative responders), leopards (4 partial responders, 4 negative responders), and bobcats (2 negative responders) gave little or no response. They also found that both males and females of the same species test alike, while reproductive-age adults are more sensitive than either aged or immature animals.

• Considers only injections of catnip oil into mice/rats.
• Another investigation of which isomers/enantiomers of nepetalactone are active, the isolated versions were tested in 9 cats with vials of the liquid; 7 responded (while the two 6-month olds didn’t and Sakurai et al 1988 attributes the non-response to their being immature, 6 months sounds old enough for reactions to have developed). The cat breeds are specified as 4 Japanese, 3 Abyssinian, and 2 American short-hairs, but not sexes (although Sakurai used a mix, given their comments that the females showed more emotional behavior than the males…the females were quite reactive, while the males were not…both of them [isomers] were extremely attractive to mature cats, especially to females). Possibly contradicting Bates & Siegel 1963’s results where only 1 isomer worked, Sakurai finds both isomers work equally well.

Confusingly, Sakurai also mentions a second experiment in impregnating filter paper with the isomers, noting that sixteen Japanese cats reacted to the 0.01mg dose; it’s unclear where these cats came from when only 9 cats (4 Japanese) were mentioned for the first experiment, and whether they were selected out of a larger group of cats or if it’s implied that it was 16 out of 16 responders - inasmuch as with catnip response rates ~70%, it would be highly improbable for all of a group of 16 cats to be catnip responders (0.716=0.3%). One possible explanation is that Japanese cats, being a historically isolated population (eg the Japanese Bobtail) after their introduction ~500AD from Korea, may have much higher population frequencies or even fixed the catnip mutation due to genetic drift or a founder effect; on the other hand, if Japanese cats were almost all catnip responders, you would think someone would have noticed by now.
• DeLuca & Kranda 1992, Environmental enrichment in a large animal facility:

TABLE 1. Number of animals, species-wide, that showed interest in various toys. Key: 0 = none, 1 = 25%, 2 = 50%, 3 = the majority of the animals. We define interest as the amount of toy destruction and/or movement that we noted in daily observations.

• …balls: catnip: 3
• balls: punch: 3
• Cat-a-Comb: NA
• Purrsuit: 3

…8-12 cats…The cats’ favorite toys - like the 12 in. giant sheepskin mice (Petraport, Anaheim, CA) - contained catnip. We hung fresh catnip in stockinette bags which the cats quickly pulled down and ultimately batted into the water bowls. We gave them catnip-treated punchball toys (Petraport, Anaheim, CA- Fig. 7)-2 in. puffs mounted by a spring to a 6 in. x 6 in. base. The cats always played with these toys, and they lasted longer than the catnip bags. The cats also had Mr. Spats’ Cat-a-combs groomer (Tarel Seven Designs, Secaucus, NJ) mounted on the walls. They usually knocked these off the wall and used them as play-things (they managed to open the compartment and dig out the catnip) rather than as grooming tools. Most of the cats spent time playing Purrsuit (Tarel Seven Designs, Secaucus, NJ)-every morning, we placed toys inside a maze and the cats chased them and tried, with a great deal of success, to get the smaller ones out. The cats had a preference for balls or bells with catnip in them, and for golf balls. They ignored the Squish balls (Ethical Inc., Newark, NJ).

So based on the reported data, we can guess that at least 5-7 cats responded to catnip of the 8-12 sample, for a best guess of 6 responders out of 10 cats. (Mixed breeds, unspecified sex.)
• Clapperton et al 1994, Development and Testing of Attractants for Feral Cats, Felis catus L.

Catnip & silvervine were tested as cat lures for trapping; simultaneous testing over multiple environments showed that catnip, silvervine, and urine all garnered substantial attention from cats. Clapperton notes that 4/4 domestics and 8/20 feral cats responded (pg7). (Sex not specified, but breeds were clearly mixed as feral cats are never single breeds.)
• McDaniel et al 2000, Efficacy of lures and hair snares to detect lynx

Used catnip and other commercial products in scent stations to look for activity of wild lynx. Todd 1963 had already found responses in lynx/puma/bobcats, so unsurprisingly McDaniel does too, but with wild lynx, it is impossible to know how many total lynx were exposed and how many reacted.
• 6 black-footed cats (Felis nigripes), catnip did interest them and cause increases in activity, but paper doesn’t break down by cat. Not useful unless want to contact authors.
• Ellis 2007, Sensory enrichment for cats (Felis silvestris catus) housed in an animal rescue shelter; apparently republished as Ellis & Wells 2009, The influence of olfactory stimulation on the behaviour of cats housed in a rescue shelter

Shelter animals were given catnip-infused clothes to play with; Ellis notes that the catnip toys were played with more than other scents on average in the catnip group, but made no effort to ascertain how many were catnip responders.
• There is apparently a vein of studies trying catnip in humans for antidepressant effects (rather than the more traditional painkiller and psychedelic effects), leading to this experiment in chronic feeding catnip to mice (ironic as that might sound), finding one antidepressant-like effect. These can’t be considered a catnip response, though.
• The 8 oncilla cats’ activity were measured over several days after each dose was introduced into their enclosures. While the doses were small (1g), the cinnamon produced statistically-significant overall average difference while catnip did not, suggesting none of the oncilla cats responded to the catnip. Nevertheless, like Wells & Egli 2004, cannot be meta-analyzed.

Potentially relevant but currently unavailable:

• Hart, B.L., 1977. Olfaction and feline behavior. Feline Practice 7(5): 8-10 (requested)
• Harney JW, Leary JD, Barofsky IB. Behavioral activity of catnip and its constituents: nepetalic acid and nepetalactone, Federation Proceedings 1974; 33: 481 (requested)

Overall, study quality is low and at high risk of bias. Key variables like sex/age/breed is almost always never reported and sometimes even n or species is not reported; placebo controls are not used; the experimenters are never blind to the substance being used; important studies are not available in English; the catnip used is not standardized; and the animals are not necessarily familiarized & comfortable with the experimenter despite the need for them to be relaxed and willing to play in order to gauge the presence or absence of a response. Probably any estimate is something of a lower bound as most of these biases would tend to mask a catnip response (like using old catnip or an animal feeling stressed), and it will be difficult to prove or disprove any sex or breed effects.

## Data

catnip <- read.csv(stdin(), header=TRUE)
Family,Genus,Species,Name,Study, Year, Responders, N, Country, Sex, Breed
Felidae,Panthera,leo,African lion,McElvain et al 1942,1942,7,7,USA,mixed,NA
Viverrinae,Civettictis,NA,NA,Todd 1962,1962,0,3,USA,mixed,NA
Viverrinae,Viverra,NA,NA,Todd 1962,1962,0,1,USA,mixed,NA
Viverrinae,Civettictis,NA,NA,Todd 1962,1962,0,2,USA,mixed,NA
Herpestinae,Herpestes,NA,NA,Todd 1962,1962,0,1,USA,mixed,NA
Herpestinae,Atilax,NA,NA,Todd 1962,1962,1,3,USA,mixed,NA
Herpestinae,Ichneumia,NA,NA,Todd 1962,1962,0,1,USA,mixed,NA
Cryptoproctinae,Cryptoprocta,NA,NA,Todd 1962,1962,0,1,USA,mixed,NA
Hyaenidae,NA,NA,hyena,Todd 1962,1962,0,1,USA,F,NA
Hyaenidae,NA,NA,hyena,Todd 1962,1962,0,2,USA,M,NA
Felidae,Panthera,leo,African lion,Todd 1962,1962,6,6,USA,M,NA
Felidae,Panthera,leo,African lion,Todd 1962,1962,8,10,USA,F,NA
Felidae,Panthera,tigris,tiger,Todd 1962,1962,1,9,USA,M,NA
Felidae,Panthera,tigris,tiger,Todd 1962,1962,7,13,USA,F,NA
Felidae,Panthera,leo/tigris,ligeress,Todd 1962,1962,0,1,USA,F,NA
Felidae,Panthera,pardus,leopard,Todd 1962,1962,6,8,USA,M,NA
Felidae,Panthera,pardus,leopard,Todd 1962,1962,8,10,USA,F,NA
Felidae,Panthera,onca,jaguar,Todd 1962,1962,4,5,USA,M,NA
Felidae,Panthera,onca,jaguar,Todd 1962,1962,3,3,USA,F,NA
Felidae,Panthera,uncia,snow leopard,Todd 1962,1962,2,2,USA,M,NA
Felidae,Panthera,uncia,snow leopard,Todd 1962,1962,2,2,USA,F,NA
Felidae,Neofelis,nebulosa,clouded leopard,Todd 1962,1962,1,2,USA,NA,NA
Felidae,Acinonyx,jubatus,cheetah,Todd 1962,1962,0,3,USA,NA,NA
Felidae,Felis,rufus,bobcat,Todd 1962,1962,1,2,USA,NA,NA
Felidae,Felis,lynx,European lynx,Todd 1962,1962,1,1,USA,NA,NA
Felidae,Felis,concolor,puma,Todd 1962,1962,2,3,USA,M,NA
Felidae,Felis,concolor,puma,Todd 1962,1962,1,2,USA,F,NA
Felidae,Felis,temmincki,African golden cat,Todd 1962,1962,1,1,USA,NA,NA
Felidae,Felis,aurata,Asian golden cat,Todd 1962,1962,0,1,USA,NA,NA
Felidae,Felis,pardalis,ocelot,Todd 1962,1962,4,5,USA,NA,NA
Felidae,Felis,wiedii,margay,Todd 1962,1962,4,6,USA,NA,NA
Felidae,Felis,serval,serval,Todd 1962,1962,0,2,USA,NA,NA
Felidae,Felis,chaus,swamp cat,Todd 1962,1962,0,1,USA,NA,NA
Felidae,Felis,manul,Pallas' cat,Todd 1962,1962,0,1,USA,NA,NA
Felidae,Felis,bengalensis,leopard cat,Todd 1962,1962,0,1,USA,NA,NA
Felidae,Felis,viverrina,fishing cat,Todd 1962,1962,0,2,USA,NA,NA
Felidae,Felis,yagouaroundi,jaguarundi,Todd 1962,1962,0,4,USA,NA,NA
Felidae,Felis,pajeros,pampas cat,Todd 1962,1962,0,1,USA,NA,NA
Felidae,Felis,catus,cat,Todd 1962,1962,8,10,USA,M,Siamese
Felidae,Felis,catus,cat,Todd 1962,1962,6,16,USA,F,Siamese
Felidae,Felis,catus,cat,Todd 1963,1963,32,43,USA,M,mixed
Felidae,Felis,catus,cat,Todd 1963,1963,26,41,USA,F,mixed
Felidae,Felis,catus,cat,Bates & Siegel 1963,1963,5,8,USA,NA,NA
Felidae,Felis,catus,cat,Palen & Goddard 1966,1966,15,26,USA,M,mixed
Felidae,Felis,catus,cat,Palen & Goddard 1966,1966,8,17,USA,F,mixed
Felidae,Felis,catus,cat,Hayashi 1968,1966,1,2,USA,NA,NA
Felidae,Felis,catus,cat,Hayashi 1968,1966,1,2,UK,NA,NA
Felidae,Felis,catus,cat,Hayashi 1968,1966,2,2,Japan,NA,NA
Canidae,Canis,lupus,dog,Hayashi 1968,1966,0,2,Japan,NA,NA
Leporidae,Oryctolagus,cuniculus,rabbit,Hayashi 1968,1966,0,2,Japan,NA,NA
Muridae,Mus,musculus,mouse,Hayashi 1968,1966,0,2,Japan,NA,NA
Muridae,Rattus,norvegicus,rat,Hayashi 1968,1966,0,2,Japan,NA,NA
Caviidae,Cavia,porcellus,guinea pig,Hayashi 1968,1966,0,2,Japan,NA,NA
Phasianidae,NA,NA,fowl,Hayashi 1968,1966,0,2,Japan,NA,NA
Felidae,Felis,catus,cat,Hatch 1972,1972,14,17,USA,mixed,mixed
Felidae,Panthera,leo,African lion,Hill et al 1976,1976,3,4,USA,M,NA
Felidae,Panthera,leo,African lion,Hill et al 1976,1976,5,5,USA,F,NA
Felidae,Panthera,onca,jaguar,Hill et al 1976,1976,1,1,USA,M,NA
Felidae,Panthera,onca,jaguar,Hill et al 1976,1976,2,2,USA,F,NA
Felidae,Panthera,pardus,leopard,Hill et al 1976,1976,2,4,USA,M,NA
Felidae,Panthera,pardus,leopard,Hill et al 1976,1976,2,4,USA,F,NA
Felidae,Panthera,tigrus,tiger,Hill et al 1976,1976,0,1,USA,M,NA
Felidae,Panthera,tigrus,tiger,Hill et al 1976,1976,0,4,USA,F,NA
Felidae,Felis,rufus,bobcat,Hill et al 1976,1976,0,1,USA,M,NA
Felidae,Felis,rufus,bobcat,Hill et al 1976,1976,0,1,USA,F,NA
Felidae,Puma,concolor,cougar,Hill et al 1976,1976,0,2,USA,M,NA
Felidae,Puma,concolor,cougar,Hill et al 1976,1976,0,2,USA,F,NA
Felidae,Felis,catus,cat,Sakurai et al 1988,1988,4,4,Japan,mixed,Japanese
Felidae,Felis,catus,cat,Sakurai et al 1988,1988,3,3,Japan,mixed,Abyssinian
Felidae,Felis,catus,cat,Sakurai et al 1988,1988,2,2,Japan,mixed,American short-hair
Felidae,Felis,catus,cat,Sakurai et al 1988,1988,16,16,Japan,NA,Japanese
Felidae,Felis,catus,cat,DeLuca & Kranda 1992,1992,6,10,USA,NA,mixed
Felidae,Felis,catus,cat,Clapperton et al 1994,1994,12,24,USA,NA,mixed

catnip$Sex <- ordered(catnip$Sex, levels=c("F", "mixed", "M"))
catnip$Country <- relevel(catnip$Country, "USA")

## Meta-analysis

### Cats’ catnip response rate

A random-effects meta-analysis on the log-odds of catnip response in domestic cats using metafor:

cat <- subset(catnip, Name=="cat")
sum(cat$Responders) / sum(cat$N)
# [1] 0.6625514403

library(metafor)
r <- rma(xi=Responders, ni=N, measure="PLO", slab=Study, data=cat); summary(r)
# Random-Effects Model (k = 17; tau^2 estimator: REML)
#
#   logLik  deviance       AIC       BIC      AICc
# -21.4749   42.9497   46.9497   48.4949   47.8728
#
# tau^2 (estimated amount of total heterogeneity): 0.1270 (SE = 0.1644)
# tau (square root of estimated tau^2 value):      0.3564
# I^2 (total heterogeneity / total variability):   25.81%
# H^2 (total variability / sampling variability):  1.35
#
# Test for Heterogeneity:
# Q(df = 16) = 21.5875, p-val = 0.1570
#
# Model Results:
#
# estimate       se     zval     pval    ci.lb    ci.ub
#   0.5642   0.1822   3.0965   0.0020   0.2071   0.9213
inverseLogit <- function(lo) { exp(lo) / (exp(lo)+1) }
inverseLogit(0.5642)
# [1] 0.6374237812

png(file="~/wiki/images/catnip-forest.png", width = 580, height = 600)
forest(r)
invisible(dev.off())

## some issues in the funnel plot of too-extreme values:
funnel(r)
trimfill(r)
# Estimated number of missing studies on the left side: 4 (SE = 2.7779)
#
# Random-Effects Model (k = 21; tau^2 estimator: REML)
#
# tau^2 (estimated amount of total heterogeneity): 0.1338 (SE = 0.1668)
# tau (square root of estimated tau^2 value):      0.3658
# I^2 (total heterogeneity / total variability):   23.46%
# H^2 (total variability / sampling variability):  1.31
#
# Test for Heterogeneity:
# Q(df = 20) = 29.2278, p-val = 0.0834
#
# Model Results:
#
# estimate       se     zval     pval    ci.lb    ci.ub
#   0.4580   0.1789   2.5603   0.0105   0.1074   0.8086

## doesn't make much of a difference because the added studies are all tiny:
inverseLogit(0.4580)
# [1] 0.6125396134

## Examine all moderators:
rall <- rma(xi=Responders, ni=N, measure="PLO", slab=Study,
mods= ~ Year + Country + Sex + Breed, data=cat)
summary(rall)
# Mixed-Effects Model (k = 10; tau^2 estimator: REML)
#
#   logLik  deviance       AIC       BIC      AICc
#  -1.3440    2.6880   20.6880    8.9263  200.6880
#
# tau^2 (estimated amount of residual heterogeneity):     0.0000 (SE = 0.1977)
# tau (square root of estimated tau^2 value):             0.0014
# I^2 (residual heterogeneity / unaccounted variability): 0.00%
# H^2 (unaccounted variability / sampling variability):   1.00
# R^2 (amount of heterogeneity accounted for):            100.00%
#
# Test for Residual Heterogeneity:
# QE(df = 2) = 1.9385, p-val = 0.3794
#
# Test of Moderators (coefficient(s) 2,3,4,5,6,7,8):
# QM(df = 7) = 12.7549, p-val = 0.0783
#
# Model Results:
#
#                           estimate        se     zval    pval     ci.lb     ci.ub
# intrcpt                   487.8630  256.4541   1.9023  0.0571  -14.7777  990.5038
# Year                       -0.2481    0.1305  -1.9004  0.0574   -0.5039    0.0078
# CountryJapan                5.2440    2.9104   1.8019  0.0716   -0.4602   10.9482
# Sex.L                       0.4818    0.2490   1.9346  0.0530   -0.0063    0.9699
# Sex.Q                      -2.4151    0.9996  -2.4161  0.0157   -4.3742   -0.4560
# BreedAmerican short-hair   -0.3365    2.1647  -0.1554  0.8765   -4.5791    3.9062
# BreedJapanese               0.2513    2.1232   0.1184  0.9058   -3.9101    4.4127
# Breedmixed                  0.8697    0.5473   1.5889  0.1121   -0.2031    1.9425

r_country <- rma(xi=Responders, ni=N, measure="PLO", slab=Study,
mods= ~ Country, data=cat)
summary(r_country)
# Mixed-Effects Model (k = 17; tau^2 estimator: REML)
#
#   logLik  deviance       AIC       BIC      AICc
# -15.8901   31.7801   39.7801   42.3364   44.2246
#
# tau^2 (estimated amount of residual heterogeneity):     0.0928 (SE = 0.1466)
# tau (square root of estimated tau^2 value):             0.3046
# I^2 (residual heterogeneity / unaccounted variability): 22.00%
# H^2 (unaccounted variability / sampling variability):   1.28
# R^2 (amount of heterogeneity accounted for):            26.97%
#
# Test for Residual Heterogeneity:
# QE(df = 14) = 14.9709, p-val = 0.3801
#
# Test of Moderators (coefficient(s) 2,3):
# QM(df = 2) = 6.2927, p-val = 0.0430
#
# Model Results:
#
#               estimate      se     zval    pval    ci.lb   ci.ub
# intrcpt         0.4493  0.1801   2.4943  0.0126   0.0962  0.8023
# CountryJapan    1.7603  0.7102   2.4786  0.0132   0.3683  3.1522
# CountryUK      -0.4493  1.4578  -0.3082  0.7579  -3.3065  2.4080
inverseLogit(0.4493)
# [1] 0.6104727898
inverseLogit(0.4493+1.7603)
# [1] 0.9011082877
power.prop.test(power=0.8, p1=inverseLogit(0.4493), p2=inverseLogit(0.4493+1.7603))
#      Two-sample comparison of proportions power calculation
#
#               n = 33.09682229
#              p1 = 0.6104727898
#              p2 = 0.9011082877
#       sig.level = 0.05
#           power = 0.8
#     alternative = two.sided
#
# NOTE: n is number in *each* group

## moderately informative Bayesian meta-analysis
## (bayesmeta doesn't support moderators/meta-regression, so estimate just mean/SD):
library(bayesmeta)
b <- bayesmeta(y = escalc(xi=Responders, ni=N, measure="PLO", data=cat),
mu.prior.mean=0, mu.prior.sd=1); summary(b)
# ...marginal posterior summary:
#                    tau            mu         theta
# mode      0.3480797501 0.5425026093  0.5264895978
# median    0.3855448743 0.5538847072  0.5440077639
# mean      0.4160027643 0.5613715973  0.5613715973
# sd        0.2619204808 0.2027041738  0.5320967280
# 95% lower 0.0000000000 0.1662104894 -0.5345947665
# 95% upper 0.8911628412 0.9718232601  1.7058585118
#
# relative heterogeneity I^2 (posterior median): 0.2893639912

inverseLogit(0.2893639912)
# [1] 0.5718404203
## multilevel tau/heterogeneity in SDs:
sqrt(1/(0.2893639912))
# [1] 1.858993011

The 2/3 rule of thumb proves to be almost exactly right, with a meta-analytic summary of 61-63% catnip response rates.

The heterogeneity of the results indicates that somethings are different from study to study or that biases like publication bias are at play; including the sex and breed covariates doesn’t help much because of the missing data, but there’s interesting trends of decreases with a study being conducted later in time and inside the USA, in line with my speculation about the Japanese studies finding catnip sensitivity to be almost universal. (The suspicious Sakurai 16/16 datapoint doesn’t enter into the full model because it has no sex information and gets dropped, so the Japanese trend there is being driven by the other Sakurai datapoints; the Hayashi results further support the Japanese anomaly.) The decrease with time is odd, but it’s much more likely that it’s reflecting differences in experimental procedure or breeds or countries than indicating that catnip response rates are being heavily selected against.2 Overall, the data quality is low as many authors (especially the chemists) did not report individual response rates or key details of the cats used such as their age, breed, or sex, which is particularly unfortunate as all the samples are small enough that the original data could’ve been easily included as short tables. This is ironic because while some authors claim that sex/breed doesn’t matter at all, others claim that females react much more strongly (or was it males?), and yet most don’t bother to break the data down by those variables, so their results can’t be pooled and an answer found!

### Cross-species catnip response rates

Catnip has been tested in a number of species. It would be interesting to include this data for several reasons: it can help the search for the genetic basis by comparing catnip-sensitive species with non-sensitive looking for genetic variants peculiar to the former, or if there is no apparent cluster of closely-related species which uniquely have catnip responses, it can test theories about what local environments might cause catnip sensitivity; it can potentially help sharpen estimates of sex/age/country/experimenter effects by borrowing strength; zookeepers can enrich their animals’ lives with catnip if they know which species respond; and since the data is already there in the papers, we might as well include it.

To examine cross-species trends, we would like to fit a multilevel model using family/genus/species, since one would expect the catnip response rate to be more similar between, say, African lions & tigers than between snow leopards & hyenas. Since each species might have different gender effects and population bottlenecks, we would ideally nest in each species the sex/country/breed/year covariates. We would also like independent random-effects for each study to allow for the heterogeneity we observed before (which could be independent of the family/genus/species hierarchy, in which case it would model things like different experimental procedures - eg catnip leaves vs extract, or the experimenter being good or bad with animals - or it could be species-specific too). Unfortunately, such a full model would require estimating a huge number of parameters (with 24 species, 14 genuses, & 6 families, 10 studies, and 4 variables for each species, that’s easily 270 parameters which must be fit) and there is far too little data (and the available data is compromised by the frequent missingness of species and sex), so we have to settle for something more modest, focusing on just the cross-species aspect.

## full model is unidentifiable due to too few data points and missingness:
# b <- bglmer(cbind(Responders, N) ~ (Sex+Country+Breed+Year|Species/Genus/Family) + (1|Study), family="binomial", data=catnip)

library(metafor)
# levels(catnip$Name) <- c(levels(catnip$Name), as.character(catnip[is.na(catnip$Name),]$Genus))
# catnip[is.na(catnip$Name),]$Name <- as.character(catnip[is.na(catnip$Name),]$Genus)
## sort by taxonomy:
catnip <- catnip[with(catnip, order(Family, Genus, Species)),]
catnip$Label <- with(catnip, Map(function(f,g,s, n) { paste0(n, " (", paste(f, g, s), ")") }, Family, Genus, Species, Name)) cross <- rma(xi=Responders, ni=N, measure="PLO", slab=Label, data=catnip) summary(cross) png(file="~/wiki/images/catnip-forest-crossspecies.png", width = 580, height = 1000) forest(cross) invisible(dev.off()) library(blme) b <- bglmer(cbind(Responders, N) ~ (1|Species/Genus/Family) + (1|Study) + Year, family="binomial", data=catnip) summary(b); ranef(b) # Survey Collecting data by hand is very slow unless I make a major effort like getting permission from a local pound to spend a day or two testing all their cats. But surveying cat owners could be a shortcut to getting a lot of data. (Only a few percent of respondents will have gone beyond catnip, but that’s still a bigger sample than I have now.) Prizes: 3$50 Amazon gift cards Survey: Mechanical Turk; Facebook? can do advertising or a boosted post to https://www.facebook.com/CatsLoveCatnip/ can do MT by sending Turkers out to a copy of the Google Docs survey and giving them a completion code at the end

sample sizes: need >33 catnip respondents per country for detecting possible Japan effect limit MT to Australia/China/Taiwan/Korea/Japan (so 5*>33 = >165 total from MT) cat-owner qualification? avoid overpaying by the <10 HIT strategy https://docs.google.com/presentation/d/1Y_lvecsOefCfkXkkrdFtW1GH-NkoZidKzKXqFVJaLH4/edit#slide=id.ga3bec7adb_1_6 so at least 19 HITs MT calculator: https://morninj.github.io/Mechanical-Turk-Cost-Calculator/ 165 responses at $0.50 reward (for high quality responses) + MT’s 20% commission =$108

preview: https://docs.google.com/forms/d/e/1FAIpQLSeT3GIg-pSwzDFAfNaqE-MzfJEtD0HghN_Vma68OZJtz1Pztg/viewform launched 29 September 2016:

demographics:

• gender
• age
• country

• sex (M/F)
• spayed/neutered
• breed: various
• fur color; used cat color list from The Relationship Between Coat Color and Aggressive Behaviors in the Domestic Cat, Stelow et al 2016:

• black
• black-and-white
• calico
• color points
• gray
• gray-and-white
• Tabby (black, brown, and gray)
• Tabby (orange, cream, and buff)
• tortoiseshell
• white
• Torbie
• other
• personality 1-5: The personality and emotional factors were found to be the most important: withdrawn cats react poorly while friendly, outgoing cats react best
• stimulants, binary: catnip response, valerian response, honeysuckle response, silvervine response, cat thyme

Catnip:

• has the person ever consumed catnip in the form of: tea / leaves or an herb / roots / smoked / poultice
• if so, what was the purpose? relaxation / stimulation / euphoria or intoxication / hallucination or visual distortion / dreams / insomnia / stomach aches / mosquito repellent / headaches / colds or flu or fever / hives / arthritis / increasing urination / treatment of worms / hemorrhoids / other
• efficacy: 1-5

Post-launch edits:

• removed free response from gender question in demographic section due to abuse
• added age constraints to the human and cat age questions due to abuse
• edited introduction to rephrase it as cat non-responses & began advertising as a catnip non-response survey: the first 49 respondents claimed that 45 of 47 cats (cat #1 responses) responded to catnip, which is grossly discrepant from the 62% estimate - it’s imprecise, but there’s no way the true catnip rate is 96%! Further, the catnip non-response rate goes up in the additional cat entries. All this indicates either a bias in respondent recollections (they only remember the cats which do respond, or they provide a responding cat’s data first and then don’t include all the rest they know of) or a response bias to experimenter demand (inferring that I want to hear only about cats which do respond). The response rates for the other substances like silvervine are more reasonable thus far (although with far smaller sample sizes) and the small sample size is what I expected because those substances are much rarer, so this may not be a general acquiescence bias (because you would expect many more people to be claiming their cat respond to all of catnip/silvervine/valerian/thyme). If it’s a recollection bias, I don’t know of anyway to correct that afterwards or change the survey to eliminate it, so surveys on this topic might be futile.

# Known cat stimulants

• Nepeta cataria (catnip) https://en.wikipedia.org/wiki/Catnip#Effect_on_cats : active ingredient nepetalactone
• Lonicera Tatarica (Tatarian Honeysuckle) https://en.wikipedia.org/wiki/Lonicera_tatarica : nepetalactone TODO: that can’t be the only ingredient if catnip doesn’t work on Percy and honeysuckle does
• Valerian:

• Valerian officinalis https://en.wikipedia.org/wiki/Valerian_%28herb%29#Effect_on_other_organisms : active ingredient actinidine
• Valeriana celtica https://en.wikipedia.org/wiki/Valeriana_celtica : active ingredients nepetalactone (Bicchi et al 1983)
• Actinidia Polygama (Japanese Catnip or Matatabi or Silvervine or silver vine or cat powder) https://en.wikipedia.org/wiki/Actinidia_polygama#Pets and Actinidia macrosperma : active ingredient Actinidine and dihydroactinidiolide

• Hayashi 1968 claims to have found no responses in an unspecified but probably >4 number of cats when testing nepetalactone (catnip) and actinidine solutions, aside from two actinidine reactions: salivation when poured into one cat’s mouth and vomiting after an injection. Oddly, Hayashi claims in the conclusion section Our experiments do not support the claim that Actinidia palygama produces behavioural changes in cats and then immediately following that in the summary section that The actinidine reflexes, called forth by the odour of the fluid, were observed in cats but not in mice, rabbits or guinea pigs., so I am left confused about what Hayashi’s results were.
• non-response rate: 3 of 31 in Katahara & Iwai 1975/Katahira 1993
• Shoyama et al 1998 notes that their cultured fruit calluses would produce only a low amount of attractant for cats, so wood/leaf is probably necessary for a response
• Sakan et al 1960a, Chemical components in matatabi. I. The isolation of the physiologically active principles, matatabilactone and actinidine [in Japanese]
• Sakan et al 1969, Biologically active C9-, C10-, and C11-terpenes from Actinidia polygama, Boschniakia rossica, and Menyanthes trifoliata (in Japanese; Tucker & Tucker summary: Sakan et al. (1969) also isolated onikulactone from B. rossica and found that it induced the catnip response in cats. None of the Sakan papers in English mention behavioral data or experiments, just chemistry.)
• Hazama N (1942) Felidae species and Actinidia polygama. Shizen [Nature] 6:55-59 [in Japanese]

A Hazama, N is mentioned several times in The Monkeys of Arashiyama: Thirty-five Years of Research in Japan and the West as one of the first researchers to study those monkeys, so apparently he was a biologist of some sort, but is listed as deceased as of 1991. The bibliography includes a 1962 publication in Iwatayama Shizen Kenkyujo Chosa Kenkyu Hokoku but it’s cited as volume 1, so can’t be the Shizen in question. Folia psychiatrica et neurologica japonica, Volumes 17-18 1963 cites Hazama twice:

• Hazama, N: Felidae and Matatabi. Shizen (Nature), 6: 55-59, 1951 (Japanese)
• Hazama, N: Cat and Matatabi. Iden (Heredity), 7: 33-37, 1953 (Japanese)
So the original citation to 1942 may be wrong or he may’ve published three almost identically-titled papers (Matatabi = Actinidia polygama).
• Acalypha indica (Indian acalypha/Indian nettle) active ingredient TODO
• cat thyme (teucrium marum) : active ingredient TODO
• Buckbean (Menyanthes trifoliata): mitsugashiwalactone

• Northern groundcone (Boschniakia rossica): boschniakine and boschnialactone
• Yellowbells (Tecoma stans): boschniakine and actinidine
• Trumpet Creeper (Campsis radicans): may boschniakine
• Guelder Rose (Viburnum opulus, sometimes called Cranberry Bush and most commonly found in cultivation as the Snowball Tree)
• the perennial Dittany of Crete (Origanum dictamnus/Hop Marjoram)
• the spring-flowering annual Baby Blue-eyes (Nemophila menziesii)
• the Zimbabwean plant Zinziba (Lippia javanica aka Verbena javanica).

Speculative:

• there are anecdotal reports that some cats are attracted to olive products: olive wood, olive oil, and olive fruits themselves

# Local cat experiments

The catnip literature has a good sample of what the catnip frequency response is, but it’s clear that a lot of cats are immune and their owners need to use one of the many substitutes. The literature does not seem to have much, if any, coverage of all the main alternatives, so owners don’t know what to try after catnip. There’s also no information on any correlations between responses: does catnip immunity cause susceptibility to a different stimulant? Are some cats more response to stimulants in general? If we know a cat is immune to, say, catnip and valerian, can we better predict what a owner should try next?

Since cats are easy to come by and the stimulants are cheap, I thought it might be interesting to assemble a collection of stimulants and systematically try them out on each cat I should happen to meet. Specifically, I’ll look at the most common and easy to come by stimulants, since it’s not useful to discover that some extinct African flower is super-potent:

• Catnip (obviously)
• Tatarian honeysuckle (one of the most frequently mentioned alternatives)
• Valerian (not as commonly mentioned, but very cheap due to its popularity as a herbal supplement for sleep & anxiety)
• Silvervine (rarer & more expensive but still accessible, and reputedly quite effective)
• Cat thyme
• Olive oil/wood (cats’ reacting to olive-related things is an obscure & anecdotal claim; but both are easy to get and included for the sake of comprehensiveness)

• Stimulants:

• Toys (need multiple to avoid cross-contamination):

• total: \$63.23

For each stimulant, one clean never-used feather was put into a clean jar along with a good helping of the relevant stimulant, and shaken and left to sit. The olive wood would not fit into a jar, so I sawed it in half, saved the sawdust, and put the two wood blocks, sawdust, and feather into a little ziplock bag. The wand lets the feathers be added or removed easily so I can test each feather one at a time by switching feathers, playing with the cat for 5 minutes, and waiting for any response or indication of interest beyond regular chase. This works well, aside from the silvervine powder where inevitably some of the powder falls off or blows out of the container, so it’s best to do the silvervine last.

## Efficacy

Cat Sex Age Fixed Color Kind Catnip Valerian Honeysuckle Silvervine Olive wood Olive oil
Oolong M 1.5 1 black Domestic long 0 1 0 1 0 0
Percy M 3 1 brown Tabby 0 0 1 1 0 0
Kiki M 2 1 grey Tabby 1
Stormy M 10 1 grey Russian Blue
Sara F 10 1 brown Tabby 1
Whitey F 5 1 white Domestic short 1
Sassy F 12 1 orange Domestic short 0 0 0 1 0 0

Description of effects:

• Catnip: too well known to need much description. Catnip responder cats become hyper, uninhibited, playful, interested in the catnip toy.

Testing it in my 2 non-responder cats in December 2014, Percy and Oolong initially sniffed it for a few seconds and then ignored it afterwards, regardless of whether I shook half a pound of catnip leaf under their nose or let the open jar sit next to them. Likewise, attempts to interest them in the catnip extract spray in November 2015 also failed. In October 2016, I purchased ~100g of dried catnip leaves at a local Renaissance festival to have a backup for the catnip extract spray and perhaps try out catnip tea myself (and if I can’t find any use for it, I can always experiment with home steam distillation of catnip oil from catnip leaves!). Retesting Percy/Oolong with the new leaves, Percy remained uninterested but this time Oolong was interested in the plastic bag containing the catnip leaves, trying to claw and chew it, so I put ~10g into a little cotton bag and give it to him, which he began to chew and claw and even laid down to hold it in his paws and kick at it - however, despite resembling the catnip response, he was not hyper, and he did not repeat the reaction on 4 subsequent occasions I tried to interest him in the catnip bag (spraying it with the catnip extract did not help). This makes me wonder if catnip response might have some ultra-long tolerance like some drugs in humans which take weeks or months for tolerance to be restored, or if the catnip response is not bimodal after all (catnip being an autosomal dominant gene would certainly seem like it almost has to produce a bimodal/binary trait, but we have only Todd 1962 as evidence for it being autosomal dominant, and he used a single small breeding colony and no one has ever followed up & tried to replicate it that I know of). Perhaps the issue of measurement error has been underestimated in past studies and many cats will only display a catnip response occasionally or under ideal conditions, and so the estimates of catnip immunity are heavily biased upwards?
• Valerian: on Oolong, produces an interesting mix of passiveness and possessiveness - after onset, he mostly lays on the floor passively, occasionally pulling himself across it towards the toy, but generally making little effort to hunt; if the toy comes within reach, though, then he seizes it energetically and abruptly begins clasping it to his face, chewing it, curling up around it and kicking at the toy with his hind legs. Eventually he can be coaxed into playing chase normally, with his usual level of competence and interest. Actively repelled Sassy.
• Honeysuckle: on Percy, had a general stimulant effect; despite being fat, lazy, and usually entirely uninterested in chase, he will make an effort to play after sniffing a honeysuckle-impregnated toy. This stimulating effect does not produce the un-inhibition of catnip, and seems fairly mild. Actively repelled Sassy.
• Silvervine:

1. on Oolong, a general stimulating effect with considerable interest in playing chase or watching the toy, but curiously, he makes many fewer attempts at attacking or chasing and when he does, he is distinctly slower (and thus, less effective) than usual. His coordination is fine - he’s not clumsy or falling over - but he’s just not as effective (in a way hard to pin down specifically).
2. On Percy, likewise a general stimulating effect but far more effective than the honeysuckle in inducing chase play, with him even trying out jumps when coaxed appropriately; he may be less effective, like Oolong, but he plays chase so little that it’s impossible for me to make any comparisons with his normal chase behavior.
3. Sassy: similar. More time on back while playing chase than usual.
• Olive oil/wood: all cats showed brief interest in smell, then ignored entirely.

# Appendix

## Does initial data support one-and-only one response per cat?

When I tested the first two cats with the 3 stimulants I had, they both responded to exactly 1 of the 3 stimulants: Oolong ignored catnip & honeysuckle while responding to Valerian, and Percy ignored catnip & Valerian to respond to honeysuckle. Honeysuckle and catnip supposedly have the same active ingredient while Valerian differs, so this is an odd pattern. Could there be something at play like a single mechanism which responds to only one chemical and so every cat responds to one-and-only-one-kind (OO) of stimulant? The existing literature doesn’t seem to describe many (any?) tests of multiple stimulants on the same cat… Is this much evidence?

Assume binary responses, that the default or null hypothesis theory here is that each stimulant has a 50% chance of working (I only know the population frequency for catnip, which is somewhat close to 50%), and they are independent; then the exact probability of drawing 1 of 3 is a binomial with 1 success of 3 trials with 50% chance of success or ~0.375 (through some combinatorics and can be checked by simulation), and then the probability of two such events is their conjunction of 0.3752=0.141. This 0.141 can be interpreted as a p-value (the frequency with which the null hypothesis generates this particular set of stimulant responses if we sampled two cats). If we didn’t believe the probability of 0.375 pulled out of combinatorics, we could do a simulation-based hypothesis test by twice generating a possible value from a binomial distribution and seeing in how many simulations both datapoints (cats) yielded exactly 1 of 3, which matches our 0.141 p-value:

simulates <- 100000
matches <- sum(rbinom(simulates, 3, p=0.5)==1 & rbinom(simulates, 3, p=0.5)==1)
matches / simulates
# [1] 0.14012

OK, so we know under a plausible alternative model, our data from 2 cats occurs fairly often, but what does that mean? A Bayesian model-comparison would be more meaningful.

In this case, we compare the binomial model with a model in which each cat responds to OO stimulant. We can use ABC to continue the theme. One might object, don’t we already know the result of an ABC? If we write a generative model for the OO theory, it will yield the data every time, and we already know the binomial theory yields the data only 14% of the time, so we get a ratio of $\frac{1}{0.14}=7$, which is an interesting level of evidence (keeping in mind that we must have a low prior on the idea of only one stimulant, since it didn’t come to mind before we saw the data).

I would say that’s not quite right, because here we have the twist that we still don’t have the silvervine data - if it’s true cats respond to only one stimulant, then silvervine could have been either cat’s special stimulant and so they would appear to have no responses in our current data. The OO theory is that it would be out of the major stimulants, which are catnip, honeysuckle, Valerian and silvervine. So we need to account for the penalty that it predicts data other than we saw (like data in which neither cat responds to any of the 3 stimulants), which makes a BF of 7 to be an overestimate.

Here for ABC we could simulate this, but again the exact answer is easy: If there’s 4 stimulants and we sample 3, and there is exactly 1 hit, the chance of observing it is $\frac{3}{4}$ (since the chance of not observing it, of it lurking in the last stimulant, #4, is $\frac{1}{4}$ and $1-\frac{1}{4}=\frac{3}{4}$); and the probability of observing this twice is $\frac{3}{4}^2$ or 0.5625. So the probability of the data under the null hypothesis is 0.141 and the probability under this alternative OO model is 0.5625, giving a ratio of 4 in favor of it (substantially less than the 7 before).

Since I find the OO theory to be ad hoc, based on looking at the data rather than modeling, and also weird - why would Percy react to honeysuckle and not catnip given that the active ingredient supposedly is nepetalactone in both? - I would give it a negligible prior probability like 1%, in which case a BF of 4 would increase only to around 4%.

In any case, after doing those calculations, I was able to try some more potential stimulants: silvervine, olive wood, and olive oil. Under the OO theory, since we had already seen a response from both cats (for valerian & honeysuckle), we should see no further responses; but unsurprisingly, I did, as both of them responded to silvervine (though neither olive). So we can probably reject the theory.

1. For example, Todd 1962’s genetic analysis was based on just 34 cats of which 7 cats’ response were unknown; as far as I can tell, another pedigree analysis has never been done since then, much less extended to newer genetic methods like linkage or GWASes, although it continues to be cited as the justification for treating catnip response as an autosomal dominant genetic trait.

2. If catnip sensitivity frequency was 70% in 1950, and for the sake of argument we accepted that the proportion had decreased ~0.0024 per year and was 54.16% in 2016, and we also accept Todd 1962’s analysis that catnip sensitivity is a dominant gene, then that implies that the frequency of the gene in 1950 was $0.7 = P^2 + 2P(1-P)$ and so in 1950 P=0.45; similarly, $0.516 = P^2 + 2P(1-P)$, and so in 2016 P=0.30, so the gene frequency would’ve fallen by 0.15 from 1950 to 2016. If a cat generation is 3 years, then that 66 years is 22 cat generations, and spreading a fall of 15% over that, the gene frequency would be falling ~0.68% per generation.

While this could be caused by fairly weak selection against catnip responders, it’s hard to imagine what could possibly cause that selection or how it is consistent with the continued existence of catnip responders given that: catnip has no known ill effects on cats, is rarely found in the wild, most cats are never exposed, those cats which are exposed at all tend to be pets which are spayed/neutered, no solid sex or breed correlation has been observed, and the existence of catnip responders has been documented for centuries (according to Tucker & Tucker 1988, John Ray, died 1705, was the first, and Gary Lockhart attributes the first mention of catnip to Al-Biruni, died 1048).