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Message: <blockquote data-quote="Olgar Shiverstone" data-source="post: 998869" data-attributes="member: 5868">Does PHP have a function that calculates percentages of a standard normal?Unfortunately, if PHP doesn't have a function that computes percentages as a function of a standard normal distribution, there really isn't an easy way to do it (which is why even in the computer age we still use Z-tables).The function that returns the percentage is:[Integrated from -infinity to X] (1 / SQRT(2 * pi)) * EXP (-1 *  (x^2)/2)So of course the integration is the problem.  You could create a numerical integration function that stepped through the entire integration at very small intervals summing rectangles as an approximation, ie (translate this into PHP or whatever):percent = 0for i = -5 to x step 0.01  percent = percent + ((1 / SQRT(2* pi)) * exp (-1 * (i^2)/2)) * 0.01nextpercent=percent*100Which should give a rough approximation (x is the normed value of the individual score ranging from -3 to +3).  Smaller steps (change all 0.01 to 0.0001, for example) will yield a more precise value.  I'm not sure exactly what method Excel uses to do this integration.Edit: Forgot the square root of 2*pi</blockquote>