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  1. J

    Constant hazard ratio and relative risk

    Hazard ratios are frequently interpreted as relative risks. I know the hazard ratio is a function a time that describes the instantanious ratio of rates. But in a Cox model we make the assumption of proportional hazards, which means that hazard ratio is constant over time. For example, if HR =...
  2. J

    z-test assumptions

    A z-test can be performed instead of a t-test when the sample size is large since the t-distribution with many degrees of freedom is similar to the standard normal distribution. In this case I understand that all assumptions for a t-test must be met. This including data from a normally...