Error #NUM! POISSON(350,350,TRUE)

  • Thread starter Thread starter Paul
  • Start date Start date
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Paul

Hi All,
I am try to use the POISSON(350,350,TRUE) probablity
function in my MS Excel worksheet and it keeps returning
the following error message:
#NUM!

Why is this haappening?
 
Probably because the Poisson function uses factorials, and 350! is a far
larger number than Excel can handle.
 
Stephen Bye said:
Probably because the Poisson function uses factorials, and 350! is a far
larger number than Excel can handle.
Click to expand...

Correct diagnosis, but no cure offerred.

Prior to Excel 2003, it was dangerous to Excel for statistical calculations
more challenging than SUM, COUNT and AVERAGE. Now, after who knows how much
additional investment but lots of hype, Excel is safe to use for VAR, STDEV
and even LINEST. It'll be a LONG TIME before it's safe to use its
distribution functions.

The best work-around is to use the functions in Ian Smith's freely available
workbook, http://members.aol.com/iandjmsmith/Examples.xls.
 
Smith's code is most accurate package that I know of for double
precision evaluation of probability functions.

However, if you want to stick with native Excel functions, and can live
with 6-figure accuracy for this problem, then you can use the
mathematically exact relationship that

Poisson(x,mean,TRUE) = ChiDist(2*mean,2*(x+1))

Excel's continuous distributions rarely give more than 6-8 decimal place
(which in the tails may be zero significant figures) accuracy. Excel
2003 improved evaluation of the Normal distribution, but did nothing for
the other continuous distributions.

Jerry
 
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