Hazard Ratio Calculator
Calculate the hazard ratio to measure the relative risk of an event occurring in one group compared to another over time.
Calculate Hazard Ratio
Table of Contents
What is Hazard Ratio?
The hazard ratio (HR) is a measure of the relative risk of an event occurring in one group compared to another over time. It is commonly used in survival analysis and clinical trials to assess the effect of a treatment on the time to an event.
- Used in survival analysis
- Measures time-to-event risk
- Accounts for follow-up time
- Important in clinical trials
Interpreting Hazard Ratio
HR > 1
Indicates increased risk in the treatment group.
HR = 1
Indicates no difference in risk between groups.
HR < 1
Indicates decreased risk in the treatment group.
Confidence Intervals
Help determine if the effect is statistically significant.
Hazard Ratio Formula
The hazard ratio is calculated using the following formula:
Where:
- E1 = events in treatment group
- T1 = time at risk in treatment group
- E2 = events in control group
- T2 = time at risk in control group
Examples
Example 1 Increased Risk
Treatment Group: 20 events, 100 months at risk
Control Group: 10 events, 100 months at risk
HR = 2.0
The treatment group has 2.0 times higher risk of the event
Example 2 No Difference
Treatment Group: 15 events, 100 months at risk
Control Group: 15 events, 100 months at risk
HR = 1.0
No difference in risk between groups
Example 3 Protective Effect
Treatment Group: 10 events, 100 months at risk
Control Group: 20 events, 100 months at risk
HR = 0.5
The treatment group has 0.5 times the risk of the event