QUESTION 5

Read the abstract below then answer the following questions:

Researchers conducted a prospective cohort study among adults aged 40-69 yearsto investigate the association between active travel to work and cardiovascular health outcomes. Potential study participants were contacted via a national primary care general practitioner (GP) list. GP practices that agreed to take part in the study were asked to mail invitation letters to all individuals aged 40-69 years in their patient registers. Participants were asked to attend an assessment centre within about 40 kilometres of their residence to complete a questionnaire and clinical measurements of cardiovascular disease risk factors.

Of the 36,500 adults aged 40-69 years contacted, 8,793 volunteered to take part in the study. The participants were in paid employment and did not always work at home. Participants were followed up every 6 months. At 24 months follow-up, 4,510 had withdrawn from the study. The researchers had complete data from 4,275 participants.

1. Identify the population of interest, sampling frame(source population), study sample, and study participants used (4 marks).

1. What type of sampling is being used? (1 mark)

1. please comment on the response rate. Why is this important? (2 marks).

1. Please suggest any factors which may undermine the representativeness of the study sample (4 marks)