Look out for comparisons where people knew which intervention they received and knowing that could have changed how they felt or behaved.
People who are given an intervention may feel better because they believe they are getting a superior treatment and expect that will make them feel better. This can happen even if the intervention isn’t actually better than the comparison. It is called a “placebo effect”.
Knowing which intervention they got and having expectations about it can also change the way people behave. For example, someone who is told that taking a supplement will make them feel more calm may also make other changes in their diet or lifestyle. So they may start feeling more calm because of those other changes, rather than because of the supplements.
One way of keeping this from happening is not to let the people who receive the interventions know which intervention they got (to “blind” them).
REMEMBER: Think about whether the people in the comparison groups knew which intervention they received and, if so, whether that may have changed how they felt or behaved.