Abstract :
The effect of true Weibull modulus and sample
size on Weibull modulus estimated by moments and
maximum likelihood methods was investigated. Results
indicated that the value of true Weibull modulus had no
effect on estimated modulus for the maximum likelihood
method, and a strong effect for the moments method,
especially when sample size was less than 30. In addition,
the distribution of Weibull modulus estimated by both
methods was investigated using the modified Anderson–
Darling statistics for goodness of fit. It was found that the
distribution was not normal, lognormal, 3-parameter Weibull,
or 3-parameter log-Weibull for the maximum
likelihood method, as reported in previous studies. For the
moments method however, the distribution of normalized
Weibull moduli was found to be lognormal for sample
sizes of 40 and above. The other three distributions showed
a significant level of lack-of-fit at all sample sizes.
