In this paper, we study three different models, each involving two Wei
bull distributions, to model failure data. We carry out a characteriza
tion of the plots on Weibull plotting paper (WPP). This allows one to
decide on the appropriateness of a particular model formulation to mod
el a given data set. For each of the three model formulations, we disc
uss parameter estimation based on the plots and illustrate their appli
cation using real data.