D. 1 – Explanation
The question is limited to the 80 patients who’ve been given bisphosphonates. Odds are a ratio of
the number of people who incur a particular outcome to the number of people who do not incur the
outcome. 40 of the 80 patients received significant pain relief. It can therefore be inferred that
40 of the 80 patients did not receive significant pain relief. Therefore the odds are 40 / 40 = 1
Odds and odds ratio
Odds are a ratio of the number of people who incur a particular outcome to the number of people
who do not incur the outcome. The odds ratio may be defined as the ratio of the odds of a particular
outcome with experimental treatment and that of control.
Odds ratios are the usual reported measure in case-control studies. It approximates to relative risk if
the outcome of interest is rare. For example, if we look at a trial comparing the use of paracetamol for
dysmenorrhoea compared to placebo we may get the following results
| Total number of patients | Achieved = 50% pain relief | |
| Paracetamol | 60 | 40 |
| Placebo | 90 | 30 |
The odds of achieving significant pain relief with paracetamol = 40 / 20 = 2
The odds of achieving significant pain relief with placebo = 30 / 60 = 0.5
Therefore the odds ratio = 2 / 0.5 = 4
