The red line shows the number of patients needed to detect different hazard ratios (HR) with a significance level (alpha) of 0.05.

INSTRUCTIONS TO CANDIDATES

ANSWER ALL QUESTIONS

Assignment

For questions 1 to 4, short and concise, but correct, answers is required (preferably in red font). Statistical software is needed to solve question number 5 and 6. The answer should be complemented with a commented syntax script which can be run from the first to the last line without halting, including code to read the data from the file system of your computer, code to create new variables, and code for the relevant statistical analyses.

The datasets for the last two questions is attached (CTC.sav, fracture_bmi.sav)

Reference to the syntax or the output produced by running the code is not sufficient. Copy the relevant output from the statistics package and comment the results in this document.

 The syntax files should not be converted to PDF/Word. 

Write your full name both inside the document and in the document name. Use “Exam Nov 2022 + your name” as subject of the e-mail. 

Ask for a delivery confirmation in your e-mail program if you want to make sure that your 

e-mail has arrived. The final results will be reported, together with individual feedback, no later than three weeks after the deadline. 

1. Study design and statistical power (2.5p)

In the planning of a phase III randomized clinical trial for comparing progression-free survival after a new treatment A compared to the conventional treatment B, the investigators made a simple power calculation (see figure below) to guide the decision on how many patients to include in the study to have 80% power. 

a) The red line shows the number of patients needed to detect different hazard ratios (HR) with a significance level (alpha) of 0.05. The label for the blue line is missing. What can you say about the significance level? Motivate briefly. (1p)

b) According to the figure, how many patients do we need to include if we want to be able to detect a 25% lower progression rate among patients treated with the new treatment compared to the old treatment? Assume no drop out and a significance level of 0.05. (0.5p)

c) When analyzing the data from the trial, the p-value for the estimated HR was 0.0003 which is much lower than the significance level used when calculating the required sample size for this trial (α = 0.05). Name at least one possible explanation to this low P-value? (1p)

 

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