Yes, there is the possibility that self-reported cases are untrustworthy. But there is no reason to think vegan cat owners would be more biased than non-vegan cat owners.

My desired outcome is simply showing that it is possible for cats to be healthy on a vegan diet. I only need one example to show that. And there are examples of such cats in the study my link had. At least for its tested disorders, reported vegan cats on average were slightly less likely to have at least one. The majority of both groups were in fact "healthy" (having no measured disorder). The difference between the healthy rates is small enough that it can be explained by variance and other factors contributing to health besides diet, and that's fine.

Before anyone starts, yes there could be health metrics not being measured that are relevant to the spirit of the idea being explored. But you need to measure easily quantifiable things. If you just asked "Is this cat healthy?", you would have some owners disqualify a cat for having a cut on their paw, and others disregarding serious concerns just because there hadn't been a diagnosis. This is as wide a scope as you can expect to explore a qualitative idea with.

Unless you are suggesting that literally every owner reporting a healthy vegan cat in the study is just lying, my claim is supported by the study. And if you thought otherwise, you invented a different claim and assigned it to me.

I genuinely want people to engage honestly with other people's arguments made in good faith. I know Lemmy is ultimately a collection of largely anonymous internet users, but still, I expected better than what I have seen in this thread.