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March 2nd, 2014, 03:59 PM   #1
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Calculating Hypergeometric Distribution in Excel

I attempting to use the hypergeometric distribution calculator in excel for the start of a problem, and I am trying to figure out my issue. This problem should have a prob/result of . The result is

Not sure if it makes a difference, but this is excel 2007 for Mac.

for

sample_s 1
number_sample 12006
population_s 12000
number_pop 3,000,000


The problem is asking about multiple lottery drawings, and this part is for a drawing that pays $25 for 12000 of the 12006 tickets drawn out of 3,000,000.
So I am transferring the data to the calculator from

The rest of the problem will apply to the other five tickets, this is just the first part.


Thanks for any help!
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March 4th, 2014, 10:28 AM   #2
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Re: Calculating Hypergeometric Distribution in Excel

Could it be a rounding issue, or am I not setting this up correctly?

Thanks for any help!
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March 4th, 2014, 10:37 PM   #3
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Re: Calculating Hypergeometric Distribution in Excel

I'd think that the reason is the limited accuracy of floating point numbers in Excel. If I can remember right (I don't have Excel anymore), the accuracy limit is about . Now, you are trying to calculate numbers like



that are far away. The trick you can do, is set your computing so that in every step you have enough accuracy. For example, your problem can be written as



If you now split this up and compute parts of the product like this



you should be able to get the result. This kind of tricks are usual when dealing with very large or tiny numbers.

Also, you can use logarithms: The logarithm of product is the sum of logarithms of individual terms, so you would end up with a sum of logarithms. If you compute the sum somehow (Excel, calculator, etc.) you can calculate the final result. I've usually used this logarithm approach since it is quite general and straightforward to code.
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