I need to calculate a minimum sample size for the chi square test.
I have two groups, sick and healthy patients, and I have a new test that should detect the sick patients. The machine tell "sick" or "healthy". I was asked to check if the results of the test (E) are independent to the status (D). This is a simple 2X2 table. What is the required sample size for the appropriate chi square test ?
under H0 my expected frequencies should reflect independence.
so you are saying that I should put in every cell in the table a size of 5 patients, so I need 10 sick and 10 healthy ?
May be Dragan was warning you about the fact that in order for chi-square test to be reliable none of the expected frequencies should be smaller that 5. I have made some search in the web, and I have realized that this is a rather controversial topic....but this is another story...
As for your question, provided that I do not know the size of your sample, you could use Fisher test instead, since you have a 2x2 table. For further info, you could jump to this link.
Hope this helps,
Outside of a dog, a book is man's best friend. Inside of a dog it's too dark to read -Groucho Marx-
thank you to both of you !
ginamarco said: "I do not know the size of your sample". Well, this is the problem, I do not have one, I need to decide how many to sample....
So you'll have to do some sample size calculations? Maybe a software like
or similar sample size calculation software can help you.
thanks, I found another software (PS), and now I understand the rationale behind the calculations.
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