A group of 100 patients with knee injuriesSolutionIn the cas

A group of 100 patients with knee injuries,

In the cases, 40 skied and 60 did not, giving the odds of being a skier for this group of 40:60 or 0.66.

In the controls, 20 patients skied and 80 did not, giving the odds of being a skier for the control group of 20:80 or 0.25.

We can therefore calculate the odds ratio as 0.66/0.25 = 2.64. The 95% CI is 1.41 to 5.02.