# CS: Compound Symmetry Structure In LMMstar: Repeated Measurement Models for Discrete Times

 CS R Documentation

## Compound Symmetry Structure

### Description

Variance-covariance structure where the variance and correlation of the residuals is constant within covariate levels. Can be stratified on a categorical variable. The default has no covariate and therefore the variance and correlation are constant within cluster.

### Usage

``````CS(formula, var.cluster, var.time, type = NULL, group.type = NULL, add.time)
``````

### Arguments

 `formula` formula indicating on which variable to stratify the residual variance and correlation (left hand side) and variables influencing the residual variance and correlation (right hand side). `var.cluster` [character] cluster variable. `var.time` [character] time variable. `type` [character] `"ho"`, `"homo"`, or `"homogeneous"`: constant variance and covariate-specific correlation. Analogous to crossed or nested random effects. `"he"`, `"hetero"`, or `"heterogeneous"`: variance and correlation specific to the level of covariates. Can be seen as more flexible crossed or nested random effects model. `group.type` [integer vector] grouping of the regressor for the correlation structure. A constant value corresponds to nested random effects (default) and a regressor-specific value to crossed random effects `add.time` not used.

### Details

A typical formula would be `~1`, indicating a variance constant over time and the same correlation between all pairs of times.

### Value

An object of class `CS` that can be passed to the argument `structure` of the `lmm` function.

### Examples

``````## no covariates
CS(~1, var.cluster = "id", var.time = "time")
CS(gender~1, var.cluster = "id", var.time = "time")

## covariates
CS(~time, var.cluster = "id", var.time = "time")
CS(gender~time, var.cluster = "id", var.time = "time")
CS(list(~time,~1), var.cluster = "id", var.time = "time")
CS(list(gender~time,gender~1), var.cluster = "id", var.time = "time")

``````

LMMstar documentation built on Nov. 9, 2023, 1:06 a.m.