A deficiency of the odds ratio as a measure of effect size.

The odds ratio is probably the most widely used measure of association for binary variables. It has many well-recognized advantages and disadvantages vis-à-vis the risk ratio. We demonstrate that for chained or conditional probabilities, odds ratios can behave paradoxically, by failing to show a reinforcement effect that is expressed very clearly when risk ratios are used. Copyright 2006 John Wiley & Sons, Ltd.