help pwmc-------------------------------------------------------------------------------

Title

pwmc-- Pairwise multiple comparisons (unequal variances)

SyntaxSyntax for pwmc

pwmcvarname,over(varname)[options]

Immediate command

pwmcistats1stats2stats3[... statsk] [,options]

where

statsis

#obs#mean#sd

Description

pwmcperforms pairwise comparisons of means. It computes pairwise differences of the means ofvarnameover the levels ofover(varname). Confidence intervals are derived using procedures allowing for unequal variances across groups.

pwmcimplements Dunnett'sC,GHandT2procedures, as proposed by Dunnett (1980), Games and Howell (1976) and Tamhane (1979).

pwmciis the immediate form ofpwmc. See immed.

Options

over(varname)is required and specifies that means are computed for each level ofvarname.

procedure(proc)specifies the procedure to be used to derive confidence intervals.procmay be any combination ofC,GHandT2and case does not matter. Default is to report confidence intervals using each of the procedures.

level(#)specifies the confidence level, as a percentage, for confindence intervals. The default islevel(95). Seeset level.

varlabeldisplays variable labels instead of variable names.

vallabeldisplays value labels instead of numeric codes.

cformat(%fmt)specifies how to format means, standard errors, and confidence limits.

Example

. pwmc wage , over(race)

. pwmci 1637 8.08 5.96 583 6.84 5.08 26 8.55 5.21

Saved results

pwmcsaves the following inr():Scalars

r(k)number of levels ofover(varname)r(ks)number of differencesMacros

r(depvar)varnamefrom which means are computedr(over)varnameinover(varname)Matrices

r(diff)differences of meansr(Var)variances of differencesr(nuhat)degrees of freedomr(ll_proc)lower limit of confidence interval using procedureprocr(ul_proc)upper limit of confidence interval using procedureprocr(A_proc)critical values using procedureproc(cf. Dunnett, 1980)

ReferencesDunnett, Charles W. (1980). Pairwise Multiple Comparisons in the Unequal Variance Case,

Journal of the American Statistical Association, 75(372), 796-800.Games, Paul A., Howell, John F. (1976). Pairwise Multiple Comparison Procedures with Unequal N's and/or Variances: A Monte Carlo study,

Journal of Educational Statistics, 1(2), 113-125.Tamhane, Ajit C. (1979). A Comparison of Procedures for Multiple Comparisons of Means with Unequal Variances,

Journal of the AmericanStatistical Association, 74(366), 471-480.

AcknowledgmentsMatthew K. Lau's 'DTK' package for R was helpful developing

pwmc.

AuthorDaniel Klein, University of Kassel, klein.daniel.81@gmail.com

Also seeOnline:

pwmean,onewayif installed: dunnett, prcomp