Hi I am doing a cross sectional study on the diagnostic value of a biomarker In cervical cancer.can I use the dobsons formula (z)2*p(1-p)/d2
And should p be the prevalence of disease or the sensitivity of the biomarker as per literature?
This formula (z)2*sn(1-sn)/d2*P where an= sensitivity as per literature and P = prevalence of disease is making my sample size too large which can't be reached due to many reasons primarily the time and finance
Can't I use the first formula.is it valid for a biomarker study?
Sorry, but you need to ue the second formula. Sensitivity and specificity are the keys to determining diagnostic value. If you can't detect changes in those measures, you can't determine the diagnostic value.
I think you should use Power, Precision and sample size function in STATA to come up with a sample size that gives your study enough power. The function allows you to determine sample size for various statistical tests (t test , z test...)
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