olumns equals to the number of levels of the factor
considered (number of strata).</p></dd>
<dt>strata</dt><dd><p>A numeric named vector storing the number of observations per strata,
and the name of each strata (names of the levels of the factor).</p></dd>

    <h2 class="hasAnchor" id="details"><a class="anchor" href="#details"></a>Details</h2>

    <p>When <code>method</code> argument is set as <code>'Barlow'</code>, this function
uses the original expression of empirical TTT presented by
Barlow (1979)
 