II. Definitions
- Hazard Rate
- First-time event frequency per unit of time (e.g. mortality rate)
- Hazard Ratio
- Frequency of an event or condition in an experimental group as compared with a control group over a specific period of time
- Hazard Ratio = (Exposed Hazard Rate) / (Control Hazard Rate)
- Typically the experimental group is exposed to an event, activity, medication or substance not shared with the control group
- Hazard Ratio <1 suggests a protective effect of the exposure (lower frequency than control group)
- Hazard Ratio >1 suggests a causative or provocative effect associated with the exposure (higher risk than control group)
- In contrast with Odds Ratio and Relative Risk, Hazard Ratios reflect an instantaneous ratio at a specific period in time (e.g. 5 year survival)
- Frequency of an event or condition in an experimental group as compared with a control group over a specific period of time