> "If someone gives up 1 lb of chicken, total consumption falls by 0.76lb in expectation."
https://forum.effectivealtruism.org/posts/fZp6Fpowmd5a8Lu2w/...
Directly: https://reducing-suffering.org/comments-on-compassion-by-the...
The mechanism is simple: if the stores are 100% responsive to your demand, your purchase directly affects supply. If they are not 100% perfect, they still have a mechanism through which they buy in bulk. So, roughly speaking, you might have a 1% chance of triggering a batch order for an extra 100 lbs when you purchase 1 lb of meat. And the same goes up the supply chain.
On the other hand, nearly all of the animal cruelty from factory farms stems from people buying meat from them. So if most people eat less meat, then factory farms actually will suffer.