title: Z-score to percentile in PHP
body: <p>I need a <a href="http://en.wikipedia.org/wiki/Standard_score" rel="nofollow">z-score</a> to <a href="http://en.wikipedia.org/wiki/Percentile" rel="nofollow">percentile</a> calculator in PHP. Is there a simple formula suitable to PHP or an already written function. What should I use?</p>