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Why: The lognormal distribution is a common competitor to the Weibull distribution for life. However it is adequate for 85-95% of all repair times.

When: Lognormal distributions are motivated by multiplicative (or proportional) events that grow with time like crack growth , molecular diffusion, and some wear out problems.

Where: In the days when plots had to be made by hand, it was the first widely used transform to convert plotted data into straight lines. Today it is simply one of an arsenal of probability tools used to obtain good curve fits to data with multiplicative type events.

These definitions are written by H. Paul Barringer and are also posted on his web site at

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