Journal ofNeurology, Neurosurgery, and Psychiatry 1989;52:817-820 Occasional review The Odds Ratio: a useful tool in neurosciences

SUMMARY The odds ratio is very useful; when used as a measure of association (or to describe the results of a randomised controlled treatment trial) it expresses both the strength and direction of the association (or size and direction of treatment effect). Its 95 % confidence interval estimates the likely degree of sampling error and provides a test of significance at the 5 % level. Authors, when reporting the results of descriptive studies, case-control studies and randomised controlled trials, should consider presenting their results this way rather than by simple significance testing with a chi squared test. The odds ratio (an unlikely name for a useful tool) has been around for a long time. ' Although it was originally used to analyse case-control studies, it has more recently been applied to other research designs-descriptive studies, randomised trials and overviews of randomised trials. Despite its widespread use in medicine, many of the basic textbooks of medical statistics mention the odds ratio only briefly, if at all