Technical Notes

This page is intended to clarify technical terms used on the evidence page:

  • HR stands for “Hazard Ratio.” A hazard ratio of 0.61 for Group A (e.g., non-smokers) relative to Group B (e.g., heavy smokers) means that the estimated chance of the outcome (e.g., death) in Group A is only 61% as large as the chance of the outcome in Group B. For example, if there were 100 expected deaths per year among 10,000 heavy smokers, there would be 61 expected deaths per year among 10,000 non-smokers.
  • d stands for “Cohen’s d,” a standardized measure of the size of a difference between groups. Cohen’s d expresses a group difference, such as between a treatment group and a control group at post-intervention, as a proportion of a corresponding standard deviation (e.g., the pre-intervention standard deviation of the treatment and control groups pooled together). For example, if the pooled baseline standard deviation was 100 scale units, then a control group gain of 10 units and a treatment group gain of 51 units would indicate a Cohen’s d of 0.41.

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