Diegeler et al. [NEJM 2013; 368: 1189-98] undertook a study of off-pump coronary artery bypass graft surgery in older patients. You should read this paper carefully before attempting to answer the following questions. Students are expected to answer all questions in a concise manner and marks will be awarded for clear and succinct answers
1) What type of study design is described here? (2 marks)

2) What type of randomisation has been used? Include details of any stratification if it has been used. (2 marks)

3) Why was the sample size increased after the interim analysis? (3 marks)

4) Using Table 1, what proportion of patients undergoing off-pump CABG had a history of myocardial infarction? (1 mark)

5) The analysis was performed on a modified intention-to-treat basis (ITT) (with all randomly assigned patients who underwent isolated CABG by the assigned surgeon included). Why is ITT preferable in comparison to a per-protocol analysis? (3 marks)

6) Details are given in Figure 1 on the numbers randomised and the numbers excluded after randomisation and at different stages of the trial. Use the information provided to construct a 2×2 table and perform a chi-squared test to evaluate whether there are any differences between allocated groups in the proportions of randomised patients included in the 30-day analysis. (8 marks)

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