Statistics for Maintenance Modelling: Continuous Lifetime Distributions 2

# The Lognormal Distribution¤

The pdf of the lognormal distribution is f(t) = if t 0 and zero otherwise. Here ln t is the natural logarithm of t. The lognormal distribution is often more appropriate for lifetime data than the normal distribution as it allows a wider variety of shapes to be modelled and it does not have the problem of negative lifetimes, as shown in these charts of f(t). As you can see, if is much larger than , then the lognormal distribution is approximately a normal distribution. Click on the charts for an interactive version in Excel where you can experiment with different values of and . |
The lognormal's mean is and its standard deviation is .