Question

Question 3

A study aims to determine the incidence of type 2 diabetes. A cohort of 200 people age 65 years or older who were initially disease –free participated in the study. One hundred and fifty people were examined at the end of 3 years. Fifty other participants from the initial cohort could not be examined, including 11 people who had died. Does this loss of participants represent a source of bias? Justify your answer. [4 points]

Question 4

A telephone survey is being administered by several interviewers in order to collect data regarding the outcome in a randomised controlled trial. Identify the key issues the researchers should have considered in order to minimise measurement error of the outcome. Discuss the impact these issues may have on the study. [4 points]

Answer 1

3) The answer is Yes. Loss of participants leads to a bias. Selection bias due to loss to follow up represents a threat to the internal validity of estimates derived from cohort studies.

In cohort studies a group of individuals are sampled from a source population and followed over time to ascertain the occurrence of an outcome of interest. Such cohort data are often analyzed using a time-to-event framework given the frequent occurrence of loss to follow up. In the analysis of time-to-event data, a common objective is to estimate survival in the source population, as well as how survival differs by levels of exposure. Selection bias due to loss to follow up, also known as informative censoring, represents a threat to the internal validity of estimates derived from cohort studies.

Please raise a separate request for Question 4.