Continuous time duration models, also known as survival models, have been used in
analysis of unemployment duration, the period of time spent between jobs, durability of
marriage, etc. Application of survival models to analyse economic data raises a number
of important issues resulting primarily from the non-controlled experimental nature of
economic observations, limited sample sizes (i.e. time periods), and the heterogeneous
nature of the economic environment within which agents operate. These issues are clearly
not confined to duration models and are also present in the case of other microeconometric
investigations that are based on time series or cross section or panel data.