BUILT-IN MATHEMATICA SYMBOL
StrataVariables
StrataVariables
is an option for fitting functions such as CoxModelFit that specifies the variables on which the model should be stratified.
- Strata variables are used to divide a non-homogenous population into homogenous subgroups. Stratification is often useful in proportional hazards modeling where the assumption of proportional hazards between subgroups may be suspect.
- Possible settings for StrataVariables include:
-
| None | treat no variables as strata |
| {v1,v2,...} | treat the variables  as strata |
- Models with a strata variable v with p levels
effectively groups the input data into p groups corresponding to the 
.
- With multiple strata variables
, ..., 
with 
levels, the input data are grouped into at most 
groups, dropping empty subgroups.
Define some data:
Fit the data, treating the second variable as a strata variable:
| Out[2]= |  |
One stratum is created for each level in the data:
| Out[3]= |  |
A parameter summary table:
| Out[4]= |  |
Fit a model with more than one strata variable:
| Out[2]= |  |
All non-empty combinations of the strata variables are used:
| Out[3]= |  |
Baseline survival rates for the strata:
| Out[4]= |  |
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