2 Replies Latest reply on Sep 26, 2018 4:37 PM by Tyler Martin

Q-Q Plot Formula

I wanted to create Q-Q plot and this is the formula i used in Tableau. Could some one please tell me how is this formula created.

5.6865*10^-11*(-14.17234*LN(1/RANK_PERCENTILE(AVG([Life exp (years)]))-1))^5

-1.6795*10^-6*(-14.17234*LN(1/RANK_PERCENTILE(AVG([Life exp (years)]))-1))^3

+0.042192*(-14.17234*LN(1/RANK_PERCENTILE(AVG([Life exp (years)]))-1))

Thanks

Smitha

• 1. Re: Q-Q Plot Formula

Hello Smitha

Do you have a sample workbook to share?  The calculation in the absence of any other data is difficult to assist further with.

Packaged workbooks: when, why, how

Thanks

Patrick

• 2. Re: Q-Q Plot Formula

Hi Smitha,

This formula appears in another forum post. I'm not totally sure of how they derived it, but my guess would be that it is the first few terms of the power series solution to the differential equation that defines the normal quantile function.

See my reply to that post for an alternative formula that uses a rational approximation.

I hope that helps!

Tyler