“…One of the predominant approaches to stochastic failure models is to descrie wear by a Lévy process, such as a Wiener process (Whitmore, 1995;Whitmore and Schenkelberg, 1997;Whitmore et al, 1998) or a gamma process (Lawless and Crowder, 2004;Padgett and Tomlinson, 2004;Park and Padgett, 2005;Liao et al, 2006). Other degradation-based approaches include using a stochastic process to model the failure rate (Aalen and Hakon, 2001) or dynamic operating environment (Kharoufeh, 2003;Kharoufeh and Cox, 2005;Kharoufeh and Mixon, 2009). Overviews of stochastic process-based failure models can be found in Singpurwalla (1995) and Lai and Xie (2006).…”