Does declawing cause harm?

August 12, 2017

(This article was originally published at Statistical Modeling, Causal Inference, and Social Science, and syndicated at StatsBlogs.)

Alex Chernavsky writes:

I discovered your blog through a mutual friend – the late Seth Roberts. I’m not a statistician. I’m a cat-loving IT guy who works for an animal shelter in Upstate New York.

I have a dataset that consists of 17-years’-worth of animal admissions data. When an owner surrenders an animal to us, we capture the main reason for the admission (as told to us by the owner). Some of the reasons are generic: owner moving to no-pets apartment, can’t afford the pet, no time, family members have allergies, etc. But some of the reasons are related to the specific characteristics of the animal: animal is aggressive, pees outside the litter box, hides and acts skittish, etc.

Much of the sheltering community has a long-standing belief that declawed cats are more likely to have behavioral problems, as compared to intact cats. I’d like to test this hypothesis by analyzing the dataset (which also contains the declawed status of all the cats admitted to us). The dataset contains around 100,000 cat admissions, and approximately 4% of those cats were declawed.

I’ve been reading your blog enough to know that you’re not fond of null hypothesis significance testing. What approach would you recommend in this situation? Can you point me in the right direction? I might be collaborating with a veterinary epidemiologist at Cornell Vet School, and possibly also with a data scientist from Booz Allen Hamilton.

My reply: I’d go with the standard approaches for causal inference from observational (that is, non-experimental) data, as discussed for example in chapters 9 and 10 of my book with Jennifer Hill. You’d compare the “treatment group” (declawed cats) to the “control group” (all others), controlling for pre-treatment variables (age, type, size of cat; characteristics of the family the cat is living with; whether the cat lives indoors or outdoors; etc.). There are selection bias concerns if the cats were declawed because they were scratching people too much.

The statement, “Declawing causes cats to be more likely to have behavioral problems,” is not the same as the statement, “Declawed cats are more likely to have behavioral problems, as compared to intact cats.” The first of these statements is implicitly a comparison of what would happen for an individual cat if he or she were declawed, while the second statement is a comparison between two different sets of cats, who might differ in all sorts of other ways.

So your analysis might be tentative. But the starting point would to be to see how the comparison looks in your data.

P.S. Speedy cat image from Guy Srinivasan.

P.P.S. Chernavsky adds this link and says that if any readers out there are interested in collaborating on this project, he has all the data and is looking for someone to help analyze it properly.

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