Table 1

Hypothetical example of missing data mechanisms applied to a randomised trial with 100 participants in each arm. We assume that the true response rate is 33.3% in the control group and 50% in the experimental group so that the estimated OR should be 2

 Missing data mechanism
MCARMARMNAR
control groupexperimental groupcontrol groupexperimental groupcontrol groupexperimental group
Completers909060607380
Non-completers101040402720
Successes in completers304520303045
Reason for dropping out10% of participants missed their appointmentYoung people (40% of the total sample) dropped out because summer started and wanted to leave for vacation40% of participants who did not see any improvement dropped out (roughly 67% in the control group and 50% in the experimental group did not see any improvement, hence on average the 40% who dropped out refers to 27 and 20 participants, respectively)
Estimated OR (using completers)2.00
95% CI (1.10 to 3.65)
2.00
95% CI (0.96 to 4.18)
1.84
95% CI (0.97 to 3.50)