     Returns the smallest number of trials we must conduct to be 95% (1-0.05)
          sure of seeing 10 failures that occur with frequency one half.
        </p>
<p>
          <a class="link" href="../../stat_tut/weg/neg_binom_eg/neg_binom_size_eg.html" title="Estimating Sample Sizes for the Negative Binomial.">Worked
          Example.</a>
        </p>
<p>
          This function uses numeric inversion of the geometric distribution to obtain
          the result: another interpretation of the result is t