Editing Survival analysis (section)

====Example survival tree analysis====

This example of a survival tree analysis uses the R{{nbsp}}package "rpart".<ref name=":1">{{Cite web|last1=Therneau|first1=Terry J.|last2=Atkinson|first2=Elizabeth J.|title=rpart: Recursive Partitioning and Regression Trees|url=https://CRAN.R-project.org/package=rpart|access-date=November 12, 2021|website=CRAN}}</ref> The example is based on 146 stage{{nbsp}}C prostate cancer patients in the data set stagec in rpart. Rpart and the stagec example are described in Atkinson and Therneau (1997),<ref>{{Cite book|last1=Atkinson|first1=Elizabeth J.|url=https://www.researchgate.net/publication/235665541|title=An introduction to recursive partitioning using the RPART routines|last2=Therneau|first2=Terry J.|publisher=Mayo Foundation|year=1997}}</ref> which is also distributed as a vignette of the rpart package.<ref name=":1" />

The variables in stages are:
*'''pgtime''': time to progression, or last follow-up free of progression
*'''pgstat''': status at last follow-up (1=progressed, 0=censored)
*'''age''': age at diagnosis
*'''eet''': early endocrine therapy (1=no, 0=yes)
*'''ploidy''': diploid/tetraploid/aneuploid DNA pattern
*'''g2''': % of cells in G2 phase
*'''grade''': tumor grade (1-4)
*'''gleason''': Gleason grade (3-10)

The survival tree produced by the analysis is shown in the figure.

[[File:Survival tree for prostate cancer.png|thumb|700px|Survival tree for prostate cancer data set]]

Each branch in the tree indicates a split on the value of a variable. For example, the root of the tree splits subjects with grade < 2.5 versus subjects with grade 2.5 or greater. The terminal nodes indicate the number of subjects in the node, the number of subjects who have events, and the relative event rate compared to the root. In the node on the far left, the values 1/33 indicate that one of the 33 subjects in the node had an event, and that the relative event rate is 0.122. In the node on the far right bottom, the values 11/15 indicate that 11 of 15 subjects in the node had an event, and the relative event rate is 2.7.