Odds Ratios are useful in summarising the effect size or magnitude of a difference in a 2x 2 table.
For example
Group |
Sober |
Drunk |
Complied |
106 |
9 |
Refused |
59 |
56 |
Odds Ratio = (106/9) / (59/56) = (106x56) / (9x59) = 11.18
The compliers were 11 times more likely to be sober than the refusers.
You can obtain a confidence interval for the odds ratio using some simple calculations or by clicking on risk under statistics in the crosstabs procedure in SPSS.