Degradation Analysis and Related Topics: Some Thoughts and a Review

Degradation is a phenomenon where certain measurements of quality characteristics deteriorate over time. When an item subject to life testing is too well made to fail, we often turn our attention to degradation measurements and hope to obtain life time information from this type of data. The first part of this paper presents a general discussion of the degradation phenomenon. The second part reviews some scattered works related to the analysis. Topics involve shelf life studies, growth curve, S-shaped curves, experimental design, stochastic process modeling, accelerated life testing and step-stress models.