1. In a case-control study, the role of the previous injury in producing arthritis of the knee is assessed. In men, 200 of 600 men with arthritis of the knee reported the previous injury, compared with 50 of 300 male controls. For women, three of 83 female cases reported the previous injury, compared with 20 of 170 female controls.

1. What is the overall crude odds ratio between previous injury and arthritis of the knee (men and women combined)? Please state your result in a sentence.

1. You suspect gender may be a third variable that is an effect modifier. Please calculate the odds ratios of previous injury and arthritis of the knee for both men and women, and state the results of each in a sentence.