Look out for treatment comparisons where the comparison groups were cared for differently.
Sometimes the people in treatment comparison groups were cared for differently in ways other than the treatments that were compared. When this happens, it is hard to know how much a difference in what happened to the two groups was because of that, and how much it was because of the treatments that were compared.
For example, if people in one group received more attention and better care than people in the other group, that could make the treatment that they received look better than it is.
One way of keeping this from happening is not to let the people who give the treatments know which people get which treatment (to “blind” them). That way they will not care for people differently because of knowing which treatment they got.
REMEMBER: Ask if the people in the treatment comparison groups received care that was different, other than the treatments being compared.