Expected odds ratio This is what you expect the odds ratio to be, ie, the odds of the outcome given presence of the property you are looking for an association with relative to the same outcome in the absence of that property This can often be determined by using the results from a previous study, or by running a small pilot studyEnglishwise, they are correct it is the odds and the odds are based on a ratio calculation It is not , however, the odds ratio that is talked about when results are reported The odds ratio when results are reported refers to the ratio of two odds or, if you prefer, the ratio of two odds ratios That is, let us writeLet us now look at the relation between the relative risk and the odds ratio (Zhang and Yu, 1998) OR= ˇ 1 1 1ˇ 1 ˇ 2 1 ˇ 2 = ˇ ˇ 2 1 2 1 1 = RR 2 1 (21) From this we see that OR is always further away from 1 than RR But, more importantly, we see that the odds ratio is close to the relative risk if probabilities of the outcome are small (Davies et al, 1998)
The Diagnostic Odds Ratio A Single Indicator Of Test Performance Journal Of Clinical Epidemiology
