Statistical analysis based on two-parameter Weibull distribution was applied to poly(acrylonitrile-butadiene-styrene) to characterize involvement of two damage types in tensile test specimens, which appear as tiny strips and uniform whitening, respectively. Analysis using Weibull distribution suggests that the probability density functions (PDF) for extension at break and total energy consumption (named toughness) give distinctively different characteristics between the two damage types. PDF curve for the tiny strips consists of a sharp peak, whereas that for the uniform whitening a broad hump. Using two-group mixed Weibull distribution, effect of pre-existing damage on the fracture process was examined. The PDF curves show that presence of one damage type (e.g., uniform whitening) tends to suppress generation of the other damage type (e.g., tiny strips) even in a test condition that would have favored the latter in virgin specimens. Involvement of the two damage types was quantified using portion for each subpopulation from the Weibull distribution analysis. POLYM. ENG. SCI., 51:573-584, 2011. (C) 2011 Society of Plastics Engineers