Meeting these objectives may involve identifying the covariates that cause or prevent an occurrence of a DCS symptom. Obviously, one also needs to assess the effect of these covariates on the DCS onset time. Some of the data were derived from NASA-sponsored tests at the Johnson Space Center and from the Brooks Air Force Base. The data set has 1322 observations of which 1154 are right-censored. The next alternative is to use parametric models which, though efficient, are too restrictive in nature.
Probability plots can be quite helpful in checking the validity of fitted parametric models.
An analysis without verification of the validity of assumptions is considered incomplete. It is possible that the inference made from such an analysis is incorrect. That is, the model is usable. Unfortunately, the residual plot in Fig. 3 suggests that the model may not be adequate.