Which one of the following study designs would be best suited to assess the incidence of secondary pelvic malignancy in patients receiving external beam radiotherapy for prostate cancer?a. Observational study
Sampling in a case-control study is determined by a disease state, not an exposure status. The controls represent the population at risk of the disease (but do not have it) and the cases that have the disease. Case-control studies can either be unmatched (the controls are selected at random from the population at risk) or matched where each case is matched with a control for potential confounding variables. In case-control studies, a form of observational study, subjects are observed and therefore not randomised. Cohort studies contrast with case-control studies in that the subjects are sampled based on their exposure, or not, to a variable of interest and then observed until the outcome being investigated occurs. Cohort studies are therefore an example of a longitudinal study design because subjects are followed over time. Data acquisition can either be prospective or retrospective. Intervention studies, which are another form of longitudinal study, do allow for randomisation of subjects to intervention or treatment groups. Randomised controlled trials (RCTs) are a true experimental study design and provide optimal evidence in healthcare on the effectiveness of treatments/healthcare interventions specific to a population of interest. RCTs should, wherever possible, incorporate some element of ‘blinding’ of subjects (patients), healthcare providers and/or data collectors to provide the most robust evidence. RCTs should be reported according to the CONSORT statement. A cross-sectional study is a descriptive study and makes estimates of features of the population of interest at a single time point or over a continuous short period of time. It is commonly used to determine prevalence of disease in a population.