Sensitivity analysis for multiple right censoring processes: investigating mortality in psoriatic arthritis

In a mortality study in psoriatic arthritis (PsA), censored observations are generated from the fact that patients fail to attend their scheduled appointments at the clinic. As a result, more than one types of right-censored observations are available. In survival analysis, the treatment of censored observations remains a concern. The assumption of ignorable censoring, although in many cases justified, is an important assumption made often for convenience rather than any other reason. In this paper we discuss a semi-parametric model for the analysis of survival data, where sensitivity analysis on quantities of interest can be performed when small levels of association between the failure and the censoring processes are assumed. Extension of the model allows for the presence of more than one censoring processes, where one may be characterized as ignorable and the other not. This model will be used to analyze the PsA mortality data, where a sensitivity analysis on parameters can be done under the assumption of non-ignorable censoring. Sensitivity analysis will also be performed in the presence of two censoring processes, one of which will be classified as non-ignorable.