This option specifies the "working" assumption for estimating the within-cluster correlation structure. If the RSTEPS=count parameter is not specified, or is equal to 0, the default assumption of independent working correlations is implemented (R=INDEPENDENT). The exchangeable working assumption is implemented when you specify either R=EXCHANGEABLE or RSTEPS=count, where count > 0. Note that EXCHANGE is an alias for EXCHANGEABLE. No matter which assumption is specified, robust variance estimators are used to obtain the variance of estimated regression coefficients, unless you specify SEMETHOD=MODEL. In this case the naive (model-based) variance estimator is used to obtain the variance of estimated regression coefficients.