I am conducting a diagnostic accuracy study which is being held in two different study sites within a particular region in Ghana.
Using the formula comprehensively explained by Negida et. al. (2019) https://europepmc.org/article/pmc/6683590, I would need prevalence (from a previous study) to arrive at my final sample size.
My question is should I look for a single prevalence from a study held in the region or do I have to look for individual prevalence specific to each study site?
Is it prevalence of the studies that your are looking for or what?. To my understanding "if you are to run the same research in your area, you need to use prevalence of similar study".
It depends on whether the prevalence is likely to be vary dramatically between the study sites and the precision you want. . You should calculate sample sizes for a range of assumptions as to estimated likely prevalence and see the effect.
eg The attached extract shows that sample size does not very much for precision of +/- 0.05 in estimating a true prevalence of 0.3-0.7 .
(From dos Santos Silva .Cancer epidemiology; principles and methods. IARC 1999)
If the prevalence is likely to vary more between sites , do a separate sample size calculation for each site.
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