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Submitted by Sean on
I was wondering if you had any guidance as to why you get a discrepancy in the design effect as reported directly by Stata with the svy commands and that calculated from using the intracluster correlation coefficient from loneway and the adjusted mean cluster size. I provide and example below borrowed from an earlier (and unfortunately unanswered) statalist question, to illustrate the problem (http://www.stata.com/statalist/archive/2004-02/msg00517.html) webuse auto7 -svyset,psu(manufacturer_grp)- -svymean mpg- reports the deff as 1.836013 Using -loneway mpg manufacturer_grp- reports the intraclass correlation as 0.36827 A formula to obtain the intraclass correlation coefficient from loneway is rho = (MSB-MSW) / (MSB + (n_o - 1) MSW) = 0.36827 where n_o = 1/(k-1) [N - sum_i (n_i^2/N] = 3.1584767 k = number of groups = 23 N = total sample size = 74 Variance Inflation Factor = 1 + (n_o - 1) rho = 1 + (3.1584767 - 1) * 0.36827 = 1.7949 The 1.7949 derived from -loneway- does not equal the value of 1.836013 that is reported for Deff from -svymean-.