Time-to-event curves

This topic is covered by the LITFL entry, Hazard Ratio, Median Ratio and Kaplan-Meier Curves. It refers to curves of events over time, eg. survival over time.

Hazard ratio

  • Hazard rate = rate at which an event happens over time
  • Hazard ratio = treatment hazard rate / control hazard rate
  • Interpreted along a measure of time, eg. over 1 year
  • "odds of winning the race" - not the margin of victory
    • HR of 1 = equal event rate between treatment and control groups
    • HR of 2 = twice the number of patients will have the event in the active treatment group
    • HR of 0.5 = half the number of patients will have the event in the active treatment group

Median ratio

  • "the margin of victory" - not odds of winning the race.
  • Median time = time at which 50% of cases "win the race"
    • Contrast with Mean time which is the average resolution rate for that group
  • This measures how much faster the treatment achieves an outcome when compared to placebo)
  • Median ratio = placebo median time / treatment median time

Kaplan-Meier curve

  • Length of time from study entry to disease end-point
  • Compares treatment group and control group
  • Median time and mean time are derived from these curves