Hello,
I have cross-sectional data on immune cell density in a disease group. Compared to controls, the disease group shows an increase in immune cell density. Now, I want to run a clinical trial with two groups with the same disease: one receiving a drug that is expected to decrease immune cell density and the other receiving a placebo. What approach should I use to estimate the sample size for these two groups?
Compare the difference in mean outcome measures between treatment and placebo groups. Determine sample size to detect a likely effect with nominated alpha significance and power.
on line calculators are available see e.g:
https://select-statistics.co.uk/calculators/sample-size-calculator-two-means/
If the required data is unavailable for the calculation of sample size in clinical trial, a pilot study is highly suggested to find such data.
For the sample size calculation, the cross sectional data will enable an estimate of population variance but you will need a guesstimate of the likely drug effect-- possibly guided by the literature or ,as suggested above ,from a pilot study.
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