Scenario: Two studies were carried out to establish if there is a link between smoking and certain types of cancer. One study was conducted in the 1950s and compared mortality rates for ex-servicemen with the general population. The second study was carried out in the early 1990s and compared the health of girls and young women aged 16–23 years who smoked, with a control group of girls of the same age who did not smoke. Neither study found evidence of a significant relationship between smoking and the certain types of cancer investigated.

What validity, reliability and generalisability issues do the two studies throw up?

In what way (if any) can the findings from the studies be compared?