Hello All:

We use Excel spreadsheets to gather and calculate data for determining the
Reference Time (Geomean) for use in the formula: PT (patients time in
seconds)/Reference Time (in seconds) raised to the power of the (reagents)
ISI. This formula determines the Patients INR which is used by the
patients Physician to determine dosing of the drug coumadin in a coagulation
assay called the Prothrombin Time.

Normally, we obtain 20 to 30 data points with the order of magnitude of
approximately 11.0 to 15.0 seconds, always two digits with one decimal place.
Excel calculates the Geomean easily with this number of data points.

We have run into a situation where an institution has multiple sites and the
data we gather can approach 400 data points, i.e., 20 data points by 20
different sites. This gives us approximately 300 to 350 usable datapoints.
The problem is that Excel will not calculate the Geomean using two digits and
a single decimal place beyond an €˜n of 274. And yes, we have observed that
the €˜n is dependant on the order of magnitude of the numbers used. Single
digits will calculate to a higher €˜n them say double or triple digits.

It appears that this phenomenon is referred to as €œoverflow€� and the Result
in the cell is #NUM!

I have two questions:

1. Is there a fix for this issue that will allow us to use Geomean to
calculate to a higher €˜n based on the numerical values that we must use?

And

2. And this might be beyond this newsgroup, but I dont know how to contact
any real mathematicians, if we by groups obtain the Geomeans of an €˜n of
20-30, 20 times and then obtain the Geomean of those, is the final Geomean
obtained legit?

Thank you for any assistance,

Bob Allen