The general log-likelihood function (without the constant) for the lognormal distribution is composed of three summation portions:
where:
Fe is the number of groups of times-to-failure data points
Ni is the number of times-to-failure in the ith time-to-failure data group
is the
mean of the natural logarithms of the times-to-failure (unknown a priori,
the first of two parameters to be found)
is the
standard deviation of the natural logarithms of the times-to-failure (unknown
a priori, the second of two parameters to be found)
Ti is the time of the ith group of time-to-failure data
S is the number of groups of suspension data points
is the
number of suspensions in the ith group of suspension data points
is the
time of the ith suspension data group
FI is the number of interval data groups
is the
number of intervals in the ith group of data intervals
is the
beginning of the ith interval
is the ending of the ith intervalThe solution will be found by solving for a pair of parameters (, ) so that 
and 
:
where:
and:
See Also:
Appendix C: Distribution Log-Likelihood Equations
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