Analysis of discrete time competing risks data with missing failure causes and cured subjects.

Abstract

This thesis is motivated by the limitations of the existing discrete time competing risks models vis-a-vis the treatment of data that comes with missing failure causes or a sizableproportions of cured subjects. The discrete time models that have been suggested to date (Davis and Lawrance, 1989; Tutz and Schmid, 2016; Ambrogi et al., 2009; Lee et al., 2018) are cause-specific-hazard denominated. Clearly, this fact summarily disqualifies these models from consideration if data comes with missing failure causes. It is also a well documented fact that naive application of the cause-specific-hazards to data that has a sizable proportion of cured subjects may produce downward biased estimates for these quantities. The existing models can be considered within the multiple imputation framework (Rubin, 1987) for handling missing failure causes, but the prospects of scaling them up for handling cured subjects are minimal, if not nil. In this thesis we address these issues concerning the treatment of missing failure causes and cured subjects in discrete time settings. Towards that end, we focus on the mixture model (Larson and Dinse, 1985) and the vertical model (Nicolaie et al., 2010) because these models possess certain properties which dovetail with the objectives of this thesis. The mixture model has been upgraded into a model that can handle cured subjects. Nicolaie et al. (2015) have demonstrated that the vertical model can also handle missing failure causes as is. Nicolaie et al. (2018) have also extended the vertical model to deal with cured subjects. Our strategy in this thesis is to exploit both the mixture model and the vertical model as a launching pad to advance discrete time models for handling data that comes with missing failure causes or cured subjects.

Iqoqa. Isisusa salo mqingo wocwaningo silethwe ukugqoza kwezindlela ezibheka ubungozi bento kanye nendlela okubhekwa ngayo imininingo ekhuluma ngokwehluleka ukuhlonza imbangela yenkinga noma ukuqhamuka nekhambi lokwelapha lokho osekuyisisulu. Izindlela ezibheka isikhathi yizona ezisaphakanyiswayo kuze kube yimanje (Davis & Lawrance, 1989; Tutz & Schmid, 2016; Ambrogi et al., 2009; Lee et al., 2018) uma kubhekwa imbangela eqondene ngqo nengozi leyo. Kuyacaca ukuthi lezi zindlela ngeke zithathwe njengezisebenza kahle uma imininingo yocwaningo iveza ukuthi ziyahluleka ukuhlonza izimbangela zokungasebenzi kahle kokucwaningwayo. Kunobufakazi obusekwa wucwaningo futhi ukuthi ukusetshenziswa ngokungacopheleli izindlela ezibheka ngqo imbangela yenkinga ngemininingo yocwaningo eveza isibalo esikhulu sezisulu ezingalashwayo kuwukuhlehlela emuva kwezokwelapha ngoba kungaletha imiphumela echemile. Izindlela ezisebenzayo okwamanje zingahlolisiswa kusetshenziswa indlela exubile yokuhlola, imultiple imputation framework (Rubin, 1987) ukuhlonza izimbangela zokungasebenzi kahle kokucwaningwayo, kodwa amathuba okukhuphula ukusebenza kwazo ukulawula isibalo sokulashwa kwezisulu ezicwaningwayo mancane kakhulu, noma nje awekho. Kulo mqingo wocwaningo, sibheka lezi zinto nokuhluleka ukuhlonza izimbangela zokungasebenzi kahle kokucwaningwayo kanye nokwelashwa kwezisulu ngesikhathi esithize esibekiwe. Ekugcineni, sigxile ekusetshenzisweni kwendlela exubile (Nicolaie et al., 2010) ngoba le ndlela iyahambelana nezinhlosongqangi zalolu cwaningo. Indlela exubile ikwazile ukwenziwa kangcono ibe yindlela ekwaziyo ukulawula izisulu esezilaphekile. UNicolaie et al. (2015) bavezile ukuthi indlela ebheka phezulu iyakwazi ukulawula ukuhlonza izimbangela zokungasebenzi kahle kokucwaningwayo. UNicolaie et al. (2018) baphinde basebenzisa indlela eya phezulu ukubheka ukwelashwa kwezisulu. Isu lethu kulo mqingo wocwaningo ukusebenzisa kokubili, indlela yocwaningo exubile kanye nendlela eya phezulu njengezindlela ezikwazi ukubheka ukubaluleka kwesikhathi kanye nokucubungula imininingo mayelana nezimbangela zokungasebenzi kahle kokucwaningwayo.