Comparing groups where individuals self-select into treatments without randomization introduces bias.

“if you people might want to go they might want to go on a Statin let's say and then other you give them a choice and the other ones might want to go on some other drug like a zetamine and they're they're they're basically selecting themselves into two groups but you could you could compare those two groups and see how they do — but you haven't it hasn't been randomized there's a there's a lot of bias that can go into that”

“maybe making a decision beforehand which will get into selection bias but it if people might want to go they might want to go on a Statin let's say and then other you give them a choice and the other ones might want to go on some other drug like a zetamide or they're they're they're basically selecting themselves into two groups but you could you could compare those two groups and see how they do um but you haven't it hasn't been randomized there's a there's a lot of bias that can go into that there could be a lot of reasons why one group is selecting a particular treatment over the other”