Dear statalist,
I am using the user-written clustersampsi (references below) to perform a power calculation for a binary outcome variable in a cluster-randomized trial.
The number of clusters is fixed at 15 per arm (k=15). A reasonable a priori estimate of the proportion in the control condition is p1=0.2, with a range of 0.1-0.3. I expect the treatment effect to be approximately 0.2, so a priori I would select p2=0.4. My goal is to calculate the average cluster size necessary to detect an effect with the standard level and power (alpha(0.05), beta(0.8)).
The last parameter remaining to be specified is rho, the intra-cluster correlation, and this is where I would like some guidance.
First, is there a range of values that are seen as reasonable ex ante?
Second, while I do not have baseline data for this population I do have some data on proportions in a sample of similar untreated clusters. Can I use these data to estimate rho? How might I do this?
Many thanks in advance for any advice.
Best,
BL
clustersampsi:
SJ-13-1 st0286 Sample-size calculations in cluster random. controlled trials
st0286 from http://www.stata-journal.com/software/sj13-1
Hemming and Marsh, "A menu-driven facility for sample-size calculations in cluster randomized controlled trials", Stata Journal 13(1), 2013.
http://www.stata-journal.com/article...article=st0286
I am using the user-written clustersampsi (references below) to perform a power calculation for a binary outcome variable in a cluster-randomized trial.
The number of clusters is fixed at 15 per arm (k=15). A reasonable a priori estimate of the proportion in the control condition is p1=0.2, with a range of 0.1-0.3. I expect the treatment effect to be approximately 0.2, so a priori I would select p2=0.4. My goal is to calculate the average cluster size necessary to detect an effect with the standard level and power (alpha(0.05), beta(0.8)).
The last parameter remaining to be specified is rho, the intra-cluster correlation, and this is where I would like some guidance.
First, is there a range of values that are seen as reasonable ex ante?
Second, while I do not have baseline data for this population I do have some data on proportions in a sample of similar untreated clusters. Can I use these data to estimate rho? How might I do this?
Many thanks in advance for any advice.
Best,
BL
clustersampsi:
SJ-13-1 st0286 Sample-size calculations in cluster random. controlled trials
st0286 from http://www.stata-journal.com/software/sj13-1
Hemming and Marsh, "A menu-driven facility for sample-size calculations in cluster randomized controlled trials", Stata Journal 13(1), 2013.
http://www.stata-journal.com/article...article=st0286
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