Excel like a finance pro.
Statistical function
WEIBULL.DIST
Returns the Weibull distribution, common in reliability and failure-time analysis.
When to use it
The Weibull distribution, the standard model for time to failure. Alpha (shape) below 1 means early failures, 1 means constant hazard, above 1 means wear-out; beta is the scale.
The shape of it
- Syntax
=WEIBULL.DIST(x, alpha, beta, cumulative)
Worked examples
Cumulative
=WEIBULL.DIST(105,20,100,TRUE) → 0.929581
Probability of failure by 105 with shape 20 and scale 100.
Density
=WEIBULL.DIST(105,20,100,FALSE) → 0.035589
Density at 105.
Exponential case
=WEIBULL.DIST(1,1,1,TRUE) → 0.632120559
Shape 1 is the exponential: 1 - e to the minus 1.
Worth knowing
- Reliability (survival) is 1 - WEIBULL.DIST(t,alpha,beta,TRUE).
- Scale beta is the time by which 63.2% have failed, whatever the shape.
- Fit alpha and beta from failure data with a Weibull plot or Solver.
Where it goes wrong
- #NUM! for negative x or non-positive parameters.
- Confusing shape and scale order (alpha then beta).
Related
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