It can be observed from Fig. 5 and Tables 1–5 that the estimates obtained via Method 4 (UWLS), Method 7 (WLS) and Method 11 (QLS) are very similar, although from a computational point of view, QLS methods are the slowest. Perhaps, the estimators obtained with more bias in this simulation study are those of the method of moments (Method 14), especially, for small sample sizes and the parameter α (see Fig. 5 and Tables 1–5).