Look out for intervention comparisons where the groups were treated differently. Comparison groups should be treated equally.
Apart from the interventions being compared, subjects in the comparison groups should otherwise receive similar treatment. If, for example, subjects in one group receive more attention and care than in the comparison group, differences in outcomes could be due to differences in the amount of attention each group received rather than due to the interventions that are being compared. One way of preventing this is to keep managers unaware of (“blind” to) which subjects have been allocated to which action.
REMEMBER: Be cautious about relying on the results of comparisons if the groups that are being compared were not treated for similarly (apart from the interventions being compared). The results of such comparisons can be misleading.