tistics. It enables to derive critical boundaries, power, drift, and confidence intervals of such designs, mostly using the alpha spending approach of DeMets and Lan (<a href="#ref-pmid7973215">1994</a>).</p>
<p>The main motivation for the development of this package was to make this area of statistics freely available for a broad audience, which is one of the reasons why all functionality is provided by a graphical user interface.</p>
<div class="section level3">
<h3 id="installation">Installation<a class=