s method. See details.</p></dd>
<dt>reference</dt>
<dd><p>A <code>data.frame</code> to be used as a reference population when weighting the survival curves or <code>NULL</code> (default). If <code>NULL</code> the survival curves are weighted in reference to the full sample supplied using <code>data</code>, regardless of the <code>variable</code> level. If a <code>data.frame</code> is supplied it needs to include all variables specified in <code>adjust_vars</code>.</p></dd>
</dl></div>
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