Reliability — When Some Units Never Fail
A life test almost always ends before every unit has failed. Those survivors are censored: you know they lasted at least that long, and nothing more. Counting them as failures makes the product look worse than it is; deleting them makes it look better. Both are silent — the curve still gets drawn.
The Weibull shape β names the failure mode: below 1 means early-life failures (assembly, infant mortality), around 1 means random external causes, above 1 means wear-out. B10 — the age by which one unit in ten has failed — is what warranty and maintenance intervals are usually built on.
The screen also shows what you would have got by ignoring censoring. Watch which row moves: B10 barely changes, while median life, mean life and β are all wrong. That is exactly why this mistake survives review.
The Weibull shape β names the failure mode: below 1 means early-life failures (assembly, infant mortality), around 1 means random external causes, above 1 means wear-out. B10 — the age by which one unit in ten has failed — is what warranty and maintenance intervals are usually built on.
The screen also shows what you would have got by ignoring censoring. Watch which row moves: B10 barely changes, while median life, mean life and β are all wrong. That is exactly why this mistake survives review.
Try it in the app
Try: Reliability tab → Load example → make sure the status column is selected → Analyse. Then set the status column to "none" and compare B50 and β.