Look out for intervention comparisons where what happened was measured differently in the comparison groups.
Sometimes, outcomes were measured or detected differently in two intervention comparison groups in a study. When this is the case, it is hard to know how much it affected the study results.
For example, the people measuring the outcomes in a comparison of intervention for speech sound difficulties might believe that one of the interventions is better. If they know who received that intervention, they may be more likely to think that those people made fewer speech sound errors when assessing their outcomes, therefore making it look as if they made more progress.
REMEMBER: Think about whether outcomes were measured the same way in the groups that were compared.