Dear All,

Hope you all are well.

I have a question regarding the following hypothetical example codes where I am comparing Sampsi and Samclus with the new updated Power Command in Stata 16 where I am determining number of observations per cluster:

Code:
sampsi `contmean' `tmean', sd(`contsd') power(0.8)

* Estimated sample size for two-sample comparison of means

* Test Ho: m1 = m2, where m1 is the mean in population 1
*                     and m2 is the mean in population 2
* Assumptions:

*         alpha =   0.0500  (two-sided)
*         power =   0.8000
*            m1 =  .170622
*            m2 =  .616529
*           sd1 =  1.11477
*           sd2 =  1.11477
*         n2/n1 =     1.00

* Estimated required sample sizes:

*            n1 =       99
*            n2 =       99

sampclus, numclus(36) rho(`rho')

* Sample Size Adjusted for Cluster Design

*   n1 (uncorrected) = 99
*   n2 (uncorrected) = 99

*   Intraclass correlation     = .138448

*   Average obs. per cluster   = 20
*   Minimum number of clusters = 36


*   Estimated sample size per group:

*      n1 (corrected) = 360
*      n2 (corrected) = 360
However, when I use the power command in stata and execute the same task for calculating number of observations per cluster, I get the following answer:

Code:
power twomeans `contmean' `tmean', k1(36) k2(36) sd(`contsd') rho(`rho') cluster

* Performing iteration ...

* Estimated cluster sizes for a two-sample means test
* Cluster randomized design, z test assuming sd1 = sd2 = sd
* Ho: m2 = m1  versus  Ha: m2 != m1

* Study parameters:

*        alpha =    0.0500
*        power =    0.8000
*        delta =    0.4459
*           m1 =    0.1706
*           m2 =    0.6165
*           sd =    1.1148

* Cluster design:

*           K1 =        36
*           K2 =        36
*          rho =    0.1384

* Estimated cluster sizes and sample sizes:

*           M1 =         4
*           M2 =         4
*           N1 =       144
*           N2 =       144
It will be great if someone can help me understand where I am going wrong or how these commands are working.