Unfair comparison

Outcomes counted in the wrong group

Look out for comparisons of nutrition interventions where people’s outcomes were not counted in the group to which they were allocated.

Deciding who gets which nutrition intervention by chance (using random allocation) helps to ensure that people across intervention comparison groups are similar before they receive the intervention.

However, sometimes people in a study do not receive or take the intervention allocated to them. These people may be different from those who take the intervention to which they were allocated. So, if study results do not include the ones not receiving or taking the intervention, the people in the comparison groups are no longer similar. To make sure that the comparison groups are similar in the results, and the comparison is fair, people should be counted and measured in the group to which they were allocated.

For example, in obese people, a comparison of weight loss surgery with a prescribed weight loss drug, people who die while waiting for surgery should be counted in the surgery group, even though they did not receive surgery. Not doing this would make surgery appear better than it actually is.

People not taking the nutrition intervention allocated to them may make the intervention appear less effective than it would if everyone had taken it.

REMEMBER: Think about whether people’s outcomes were counted in the intervention comparison group to which they were allocated to.