**20**wrote:

Hello everyone,

Im trying to perform Fisher's exact test in R. Im calculating odds ratio like this

(no.of successes in my set) X (no. of failures in background set) / (no.of successes in background set X no. of failures in my set)

In the denominator i get 0 for some cases because failures in my set are 0 for some cases.

Can anyone tell me how to calculate p-values from odds ratio? Also what does it mean if we say odds ratio should be greater or less than 1?if I want to test over-representation in my set against the background set what should be the odds ratio and how can I calculate that?

Many thanks.

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