Unfair comparison

Indirect comparisons

Look out for comparisons of nutrition interventions between studies that are different.

For many conditions (for example, child malnutrition) there are more than two nutrition interventions (for example, nutrition education for caregivers, providing a nutrition supplement, etc.). All the possible nutrition interventions for a condition are very rarely compared in a single study, so it may be necessary to consider indirect comparisons among interventions.

For example, there may be studies comparing nutrition education to ‘usual care’, and other studies comparing the provision of a nutrition supplement to ‘usual care’, but no studies that directly compare nutrition education with the nutrition supplement directly. In this case, people making a decision about what nutrition intervention to use might indirectly compare nutrition education with providing the nutrition supplement by examining how each intervention compared to ‘usual care’.

However, there can be important differences between studies when nutrition interventions are indirectly compared. For example, the participants might have been more or less sick in some studies, or ‘usual care’ might have differed across studies. These differences between the studies can make the difference in outcomes for nutrition education and providing the nutrition supplement seem smaller or larger than it actually is.

REMEMBER: When indirect comparisons are needed to inform which nutrition intervention to choose, think about whether careful consideration was given to differences between studies.