Look out for intervention comparisons where the comparison groups were cared for differently.
Apart from the intervention that is being considered, the subjects (e.g. plants or animals) in intervention comparison groups should be treated in the same way for everything else.
For example, if livestock in one group received more attention and better care than livestock in the other group, that could make the intervention that they received look better than it is.
One way of keeping this from happening is not to let the people who give the interventions know which subjects get which intervention (to “blind” them). That way they will not care for the groups differently because of knowing which intervention they got.
REMEMBER: Think about whether the subjects in the intervention comparison groups were treated similarly (other than the interventions being compared).