Hi all,

I am testing proportion differences between two independent samples, e.g., the proportion of crime rates between servicemen group1 and servicemen group2, using "prtest" command in Stata. Then I need to provide effect size.

I wonder if I can use cohens'd, followed by the "prtest" command. I normally use cohen's d when testing mean differences (after t-test), can it be used for binary outcome variables?


Code:
estpost prtest sm_convict, by(sm_group)

             |      e(b)   e(count)      e(se)     e(se0)       e(z)     e(p_l)       e(p)     e(p_u)     e(N_1) 
-------------+---------------------------------------------------------------------------------------------------
 sm_convict |  .0075073      4645   .0084651   .0084559   .8878214   .8126816   .3746369   .1873184       2249 

             |    e(P_1)     e(N_2)     e(P_2) 
-------------+---------------------------------
  sm_convict |  .0951534      2396   .0876461 

esize twosample sm_convict, by(sm_group) cohensd

Effect size based on mean comparison

                               Obs per group:
                            spouse responded =      2,249
                               spouse didn't =      2,396
---------------------------------------------------------
        Effect Size |   Estimate     [95% Conf. Interval]
--------------------+------------------------------------
          Cohen's d |    .026063   -.0314853    .0836084
---------------------------------------------------------
In this case, can I report the difference between two sample is 0.75 (9.5% vs. 8.8%), and the effect size is 0.03 (very small)?

Thank you!

Maggie