s:</p>
<ul>
<li><code>impurity</code> or <code>impurity_corrected</code>: it's the unbiased heterogeneity reduction developed by <a href="https://doi.org/10.1198/106186008X344522">Sandri &amp; Zuccolotto (2008)</a></li>
<li><code>permutation</code> it's unnormalized as recommended by <a href="https://bmcbioinformatics.biomedcentral.com/articles/10.1186/1471-2105-11-110">Nicodemus et al</a>.</li>
<li><code>normalized_permutation</code> it's normalized version of the
    permutation importance computations by