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Hello, i hope you don't mind a biologist interloping on your boards :)

I have a statistics problem that i could do with some help with if anyone can (please!).

I'm taking 2 8ml samples from a volume of 200mls. Distributed evenly within the 200mls may be bacteria. If a sample gets 1+ bacteria in then the sample is flagged as positive, if it get 0 bacteria it is flagged as negative. I don't know how many bacteria are in the 200mls or in the samples, only positive or negative.

To make it more interesting each 200ml volume may or may not contain bacteria (but if it does the number of bacteria is a constant value).

Now i have tested 20,000 lots of 200mls. Of these 10 have flagged positive. 5 of these were positive in both samples, 5 only in 1 sample. What i really want to know is how many i have missed.

I was thinking that you should be able to use the data showing 5 in 2 samples, 5 in 1 sample only to estimate the number of bacteria in a 200ml volume (? binomial dist or similar) and then use that to determine a probability that both samples will have no bacteria in them from a 200ml volume containing bacteria.

Thankyou for reading and i'll throw in a little irrelevant factoid for your amusal: Your body has on and in it 100 Trillion bacteria, thats 10x the number of cells that make you up :yuck:

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# Its deciding which Stats method to use that the problem

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