Hazard Ratio

The hazard ratio compares the hazard or risk of an event occurring at any given point in time between two groups.

Consider λ(t) as a hazard rate at time t, which measures how fast a proportion of a population will survive till time t is decreasing at that moment.

In other words, it can be the proportion of people who will die out of those who are alive till time t.

Now, the hazard rates for control group A and experimental group B can be expressed here as λA(t) and λB(t), respectively. So, the ratio of λB(t) and λA(t) is the hazard ratio denoted as θ(t).

A hazard ratio below 1 suggests that an event such as death is less likely in the experimental group favoring experimental treatment.

A hazard ratio above 1 indicates a higher likelihood of death in the experimental group favoring control treatment.

Lastly, hazard ratio 1 means the same likelihood of death for both control and experimental treatments.