Hazard Ratio

Definition

A hazard ratio is a measure used in survival analysis to compare the rate at which an event occurs over time between two groups or conditions. A hazard ratio above 1 usually indicates a higher event rate in the exposed or comparison group, while a hazard ratio below 1 usually indicates a lower event rate, depending on how the groups are defined. [1] [2]

Why It Matters in Ageing Research

Hazard ratios are common in ageing research because many outcomes are time-to-event outcomes, such as mortality, disease diagnosis, disability, institutionalisation, or loss of function. They allow researchers to compare how quickly these events occur between groups while accounting for differences in follow-up time and censored observations. [1] [3]

Common Confusion

• A hazard ratio is not the same as a risk ratio or odds ratio.
• A lower hazard ratio does not mean an event has been prevented; it means the event rate over time is lower in the comparison being analysed.
• Hazard ratios can be misleading if the proportional hazards assumption is not appropriate.

Related Reading

• Dysbiosis
• Inflammaging
• Immunosenescence

References

1. Shreffler, J., & Huecker, M. R. (2023). Survival Analysis. StatPearls. NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK560604/
2. Sashegyi, A., & Ferry, D. (2017). On the interpretation of the hazard ratio and communication of survival benefit. The Oncologist. https://pmc.ncbi.nlm.nih.gov/articles/PMC5388384/
3. Hernán, M. A. (2010). The hazards of hazard ratios. Epidemiology. https://pmc.ncbi.nlm.nih.gov/articles/PMC3653612/