It is important to measure outcomes in everyone who was included in the comparison groups.
Learners in intervention comparisons who are not followed up to the end of the study may have worse or better outcomes than those who were followed up. For example, they may have dropped out because the intervention was not working or because they felt it was unnecessary.
Be cautious about relying on the results of intervention comparisons if many people were lost to follow-up, or if there was a big difference between the comparison groups in the percentages of people lost to follow-up. The results of such comparisons can be misleading.
BEWARE of claims that are based on studies where not all participants were followed up.
REMEMBER to check if all participants were followed up.