# StrataVariables

StrataVariables

is an option for fitting functions such as CoxModelFit that specify the variables on which the model should be stratified.

# Details

• Strata variables are used to divide a non-homogeneous population into homogeneous 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 vi as strata
• Models with a strata variable v with p levels {s1,,sp} effectively group the input data into p groups corresponding to the si.
• With multiple strata variables v1, , vk with pvi levels, the input data is grouped into at most pvi groups, dropping empty subgroups.

# Examples

## Basic Examples(2)

Define some data:

Fit the data, treating the second variable as a strata variable:

One stratum is created for each level in the data:

A parameter summary table:

Fit a model with more than one strata variable:

All non-empty combinations of the strata variables are used:

Baseline survival rates for the strata:

Wolfram Research (2012), StrataVariables, Wolfram Language function, https://reference.wolfram.com/language/ref/StrataVariables.html.

#### Text

Wolfram Research (2012), StrataVariables, Wolfram Language function, https://reference.wolfram.com/language/ref/StrataVariables.html.

#### CMS

Wolfram Language. 2012. "StrataVariables." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/StrataVariables.html.

#### APA

Wolfram Language. (2012). StrataVariables. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/StrataVariables.html

#### BibTeX

@misc{reference.wolfram_2024_stratavariables, author="Wolfram Research", title="{StrataVariables}", year="2012", howpublished="\url{https://reference.wolfram.com/language/ref/StrataVariables.html}", note=[Accessed: 21-June-2024 ]}

#### BibLaTeX

@online{reference.wolfram_2024_stratavariables, organization={Wolfram Research}, title={StrataVariables}, year={2012}, url={https://reference.wolfram.com/language/ref/StrataVariables.html}, note=[Accessed: 21-June-2024 ]}