ss="comment">// sample standard deviation</span>
</pre>
<p>
            Returns the number of degrees of freedom required to obtain a 95% probability
            that the observed differences in means is not down to chance alone. In
            the case that a borderline Students-t test result was previously obtained,
            this can be used to estimate how large the sample size would have to
            become before the observed difference was considered significant. It
            assumes, of course