Clinical trials describe study results, which are essentially time-to-event data on risks, followed systematically from the standpoint of an event of interest, using the term Hazard Ratio (HR). HR gives the comparison of two risks positioned side by side on a survivorship plot. A survival plot can represent the number of people remaining alive in the study period, the time to disappear a pain, the time to recover from a disease in the presence of an intervention drug and so on.
Kaplan – Meier plot is a curve with time on the x-axis, and the proportion (or number) of people surviving is on the y-axis. For estimating the HR, the Kaplan – Meier plot should have two curves – one representing the intervention (experimental) group and the other the control (placebo) group.
Chilli pepper study
The famous 2019 paper on chilli pepper is an example to illustrate the hazard ratio. The researchers have followed a group of 22811 for about eight years and recorded the survival plot. The group had 15122 chilli eaters (experimental group) and 7689 non-chilli eaters (control group). A total of 1236 people had died by the end of the study, of which 500 were non-chilli eaters, and 736 were chilli takers. Let’s calculate:
Risk of death for chilli eaters = 736 / 15122
Risk of death for non chilli takers = 500 / 7689
The ratio = (736 / 15122) / (500 / 7689) = 0.75.
We will call the ratio the hazard ratio (HR) for the chilli eaters.
When the team looked at the specific cause of death, Cardiovascular disease (CVD), they found the following:
Risk of CVD mortality for chilli eaters = 251/ 15122
Risk of CVD mortality for non chilli takers = 193/ 7689
Hazard ratio = (251/ 15122) / (193/ 7689) = 0.66
So what are you waiting for? Eat your chilli and postpone the eventuality!
Bonaccio et al., Journal of the American College of Cardiology, 7 4 (25), 2019
Kaplan – Meier estimator: wiki
