Goodness of fit Testing for Left truncated Two parameter Weibull Distributions with Known Truncation Point
The left truncated Weibull distribution is used in life time analysis, it has many applications ranging from financial market analysis and insurance claims to the earthquake inter arrival times. We present a comprehensive analysis of the left truncated Weibull distribution when the shape, scale or both parameters are unknown and they are determined from the data using the maximum likelihood estimator. We demonstrate that if both the Weibull parameters are unknown then there are sets of sample configurations, with measure greater than zero, for which the maximum likelihood equations do not possess non trivial solutions. The modified critical values of the goodness of fit test from the Kolmogorov Smirnov test statistic when the parameters are unknown are obtained from a quantile analysis. We find that the critical values depend on sample size and truncation level, but not on the actual Weibull parameters. Confirming this behavior, we present a complementary analysis using the Brownian bridge approach as an asymptotic limit of the Kolmogorov Smirnov statistics and find that both approaches are in good agreement. A power testing is performed for our Kolmogorov Smirnov goodness of fit test and the issues related to the left truncated data are discussed. We conclude the paper by showing the importance of left truncated Weibull distribution hypothesis testing on the duration times of failed marriages in the US, worldwide terrorist attacks, waiting times between stock market orders, and time intervals of radioactive decay.