Contribution to the discussion of ‘Survival models and health sequences’ by W. Dempsey and P. McCullagh

Excerpt

According to the Danish philosopher Kierkegaard (1843): ‘Livet må leves forlæns, men forstås baglæns’ (‘Life must be lived forwards but understood backwards’). This famous quotation seems relevant for understanding the background of the paper by Dempsey and McCullagh because their ‘chief motivation ... is the effective alignment of patient records for pattern matching and signal extraction’. The authors argue that alignment according to time of death is often the most effective way of detecting signals for what they term the ‘survival-process’. This consists of a survival time, T and a (possibly multivariate) process Y(t) which for \(t<T\) gives the health status of a subject at time t and for \(t\ge T\) takes a value \(Y(t)=\flat \) indicating an absorbing death state. The authors emphasize that death is a special state for the survival-process whereby immortal marker processes are avoided altogether. This is much in line with earlier work where Y(t) is a multi-state process in which death is an absorbing state (e.g., Andersen 1986; Andersen et al. 1991). …