SURVIVAL ANALYSIS - THE IMPORTANCE OF CENSORED OBSERVATIONS

We have considered the issue of predicting from diagnosis of a conditi on such as malignant melanoma survival past an often arbitrarily chose n fixed time-point, such as 5 years. Prediction of survival past any t ime-point becomes rather complicated due to the presence of 'censored observations', and these observations are often ignored in any analysi s. Censored observations are subjects who either die of causes other t han the disease of interest or are lost to follow-up. The aim of this paper is to show that the result of ignoring these 'censored observati ons' is an underestimation of the probability of survival beyond the f ixed time-point. Ignoring these censored observations results in poten tially valuable information on survival being thrown away. This undere stimation will often prove to be of considerable magnitude and depende nt on the proportion of censored observations present in the data. It is therefore essential to carry out a full actuarial survival analysis which will incorporate all the information contained in these censore d observations.