“…(i) the most formal method, which uses functional analysis to study the governing equation of a given problem with non-deterministic variables, and (ii) one which uses numerical methods or mathematical techniques, such as Monte Carlo, to statistically understand the problem. Others techniques, based for example on Galerkin method, are discussed and presented in Ghanem (1999), Deb et al (2001), Babuška et al (2004), Wan & Karniadakis (2006), Ma & Zabaras (2008) and Azevedo (2009).…”