A norm-table from a psychological test is giving percent ranks (PR).

How can I transform those into t-values by calculation? (Assuming normal distribution.)

I found a lot of references on how to transform z --> t, but none on PR --> t.

Way back in university, we had tables with the bell-curve, to look up PR, z-values, t-values and stanines - but how to calculate?


1 Answer 1


If Excel is available to you, you can use the t.inv and norm.invfunctions. For the other direction (to get the probability from the t- or z-value), then use the t.dist and norm.dist functions. You'll get the same figures as with the tables.


In PHP, this looks right:

  • stats_cdf_normal (p, mean, sd, 1): returns float x which bounds cumulative probalility $p$
  • stats_dens_normal (x , mean, sd): returns float cumulative probability


  • stats_cdf_t (par1, par2, which): calculates any one parameter of the T distribution given values for the others.
  • stats_dens_t (x, dfr)

This is all from http://php.net/manual/en/ref.stats.php

  • $\begingroup$ thanks for your advice! I do have excel, but would like to code a php-solution to be able to do this online. $\endgroup$
    – michi
    Feb 24, 2013 at 9:20
  • $\begingroup$ If you don't get an answer here, you could ask to close this question (I'm told it's very important), and migrate it on another SE site... Maybe stackoverflow: stackoverflow.com/questions/tagged/php $\endgroup$ Feb 24, 2013 at 14:09
  • $\begingroup$ thanks, I'd like to leave it open, though, I still hope :-) $\endgroup$
    – michi
    Feb 24, 2013 at 14:26
  • $\begingroup$ Do the functions from my last edit work? Can you try them? $\endgroup$ Feb 24, 2013 at 14:53
  • $\begingroup$ wow!!! didn't think about that, thanks!!! $\endgroup$
    – michi
    Feb 24, 2013 at 15:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.