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 | ||||||
|---|---|---|---|---|---|---|
| MCAR | MAR | MNAR | ||||
| control group | experimental group | control group | experimental group | control group | experimental group | |
| Completers | 90 | 90 | 60 | 60 | 73 | 80 |
| Non-completers | 10 | 10 | 40 | 40 | 27 | 20 |
| Successes in completers | 30 | 45 | 20 | 30 | 30 | 45 |
| Reason for dropping out | 10% of participants missed their appointment | Young people (40% of the total sample) dropped out because summer started and wanted to leave for vacation | 40% 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) | |||