witching to use the Students t distribution (or Normal distribution
          for infinite degrees of freedom) centered at delta, when δ / (4 * ν) &lt;
          epsilon for the floating-point type in use. <a href="https://svn.boost.org/trac/boost/ticket/7259" target="_top">#7259</a>.
          It was found that the incomplete beta was suffering from serious cancellation
          errors when degrees of freedom was very large. (That has now been fixed
          in our code, but any code based on Didonato 