Test Yourself

In a famous study on the effects of smoking Sir Richard Doll followed a large group of doctors for many years and related their cause of death to many of their characteristics including whether or not they were smokers. Which of the following words or phrases best describes this type of design?

Researchers studied the risk of venous thromboembolism in women using third generation oral contraceptives compared to women using levonorgestrel (Jick et al., 2000 BMJ).

They searched the General Practice database for a defined 7 year period (1993-1999), to extract the lengths of time each woman used oral contraceptives within this period and they noted which type she used.  For each group they added together the time (in years) each woman use the oral contraceptive to give a total number of years of 'exposure' for each group. They identified how many women within each group developed idiopathic venous thromboembolism during the study period.  They then calculated the incidence rate in each group (= number of cases of idiopathic venous thromboembolism /number of years exposure) and the ratio of the incidence rates.

What type of study is this?

Young men who had been part of a Danish birth cohort study were approached once more between the ages of 18-21 years and asked to provide sperm samples for analysis.

The samples were analysed for vitamin D status and concentrations of several hormones, as well as for sperm motility and concentration. In their paper, the researchers reported the relationships they found between vitamin D, hormone status and sperm count and motility.

What kind of study was this?