hazard-rate · shipping

Hazard rate

The hazard rate is the instantaneous event rate at a given time conditional on the event not having occurred before that time.

For a continuous lifetime T, h(t) = f(t) / S(t), with units of inverse time, not percent probability. Specify the clock and event: device age until first failure and time since the last replacement anywhere in a cluster are different random variables. A constant hazard gives exponential survival; neither constant hazard nor independence is established by a pooled AFR.

Relations

related

afr, mtbf, drive-day, right-censoring, left-truncation

Citations

1. NIST e-Handbook: Failure (or hazard) rate (8.1.2.3) (accessed 2026-10-10)
2. NIST e-Handbook: Exponential distribution (8.1.6.1) (accessed 2026-10-10)
3. Schroeder and Gibson: Disk failures in the real world, FAST 2007, sections 2.4 and 5.3 (accessed 2026-10-10)
4. Hesela: AFR is a rate, not a one-year failure probability (accessed 2026-10-10)
5. Hesela: Missing SMART ages and the limits of drive-age comparisons (accessed 2026-10-11)

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