in which these variables exist. All variables (both vars and strata) must be in this data frame.</p></dd>
<dt>factorVars</dt>
<dd><p>Numerically coded variables that should be handled as categorical variables given as a character vector. Do not include factors, unless you need to relevel them by removing empty levels. If omitted, only factors are considered categorical variables. The variables specified here must also be specified in the <code>vars</code> argument.</p></dd>
<dt>includeNA</dt>
<dd><p>If TRUE