To test the proportional hazards assumption, we plot the logs of the proportions surviving in each group over time, and if the lines are parallel, then the assumption is met.

Question

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The proportional hazards assumption states that the hazard ratio between two groups is constant over time. If the lines in the log-log survival plot are parallel, then the hazard ratio is constant, and the assumption is met.

To Test the Proportional Hazards Assumption, We Plot the Logs