Summary risk ratios (RRs) as estimated when the missing data are ignored (available case), by naïve imputation methods (best-case and worst-case) and by methods that properly account for the uncertainty in missing data (Gamble-Hollis and informative missingness OR (IMOR) models). Summary risk ratios (RRs) as estimated when the missing data are ignored (available case), by naïve imputation methods (best-case and worst-case) and by methods that properly account for the uncertainty in missing data (Gamble-Hollis and informative missingness OR (IMOR) models). Both IMOR models assume that the odds of the outcome in the missing data are equal to the odds in the observed data (mean IMOR=1) and reflect the uncertainty of this assumption by allowing for a non-zero SD of the missing parameter. Anna Chaimani et al. Evid Based Mental Health 2014;17:111-116 Copyright © by the BMJ Publishing Group Ltd, Royal College of Psychiatrists & British Psychological Society. All rights reserved.