In research, what does "rate of attrition" mean?

Question

While comparing different types of treatment in a research article, I read "Rates of attrition did not differ across...[the different types of treatment]." What exactly does "rates of attrition" mean in this context?

Answer 1

In this case it would mean the "dropout rate".

It's the amount of people dropping out of the study or dropping the treatment before the study was finished.