Thursday, May 21, 2009

Excel and statistics

I am using Excel 2007 a lot for data entry and reporting. So I was wondering about an old bug wrt the GAMMADIST function I stumbled upon when I wanted to compare my implementation of the Incomplete Gamma function with Excel. Well,

=+GAMMADIST(0.1,0.1,1,TRUE)

still produces #NUM!. This particular bug is known here.

There are other reports about accuracy issues with older versions of Excel, see e.g.:

There have been improvements in Excel XP/2003, but some issues remained:

In case you want to know the answer for the above formula, let’s use my implementation from GAMS:

1  scalar s;
2  s = gammareg(0.1/1,0.1);
3  option s:8;
4  display s;

----      4 PARAMETER s                    =   0.82755176 

I don’t think this is a particularly difficult point to evaluate. Nothing strange going on here. So I don’t understand why Excel has problems here.