Look out for intervention comparisons where the comparison groups were cared for differently.
Sometimes the people in intervention comparison groups were cared for differently in ways other than the interventions that were compared. When this happens, it is hard to know how much it affected the study results.
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: Think about whether the people in the intervention comparison groups received care that was different, other than the interventions being compared.