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  • Margins after pkcross

    Hi all,

    I am trying to verify results from SAS regarding a 2X2 bio equivalence study. I ran pkcross in Stata 16 v.1 and got the same results for the model parameters which are sequence, subject, treatment and period. Then, I have tried to ran margins and got the following error message:

    . margins treatment
    variable c1 not found
    r(111);

    Is it possible to run margins after pkcross ?

    Thank you very much in advance for your help.

    Best regards,

    Dimi

  • #2
    Originally posted by Dimi Arv View Post
    Is it possible to run margins after pkcross ?
    Not directly, no.

    You'll notice that the command's help file doesn't mention any postestimation commands, such as margins. That's because pkcross creates a couple of temporary variables (I think for display purposes) and then calls anova using them. After the pkcross completes, these temporary variables vanish and make the usual postestimation commands impossible.

    Nevertheless, you can fit the same ANOVA model manually, and then margins becomes accessible. See below.

    .ÿ
    .ÿversionÿ16.1

    .ÿ
    .ÿclearÿ*

    .ÿ
    .ÿwebuseÿpkdata
    (FictionalÿDrugÿConcentrationÿData)

    .ÿpkcollapseÿtimeÿconc1ÿconc2,ÿid(id)ÿkeep(seq)ÿstat(auc)
    ................................
    .ÿpkshapeÿidÿseqÿauc*,ÿorder(RTÿTR)

    .ÿpkcrossÿoutcome
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿsequenceÿvariableÿ=ÿsequence
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿperiodÿvariableÿ=ÿperiod
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿtreatmentÿvariableÿ=ÿtreat
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿcarryoverÿvariableÿ=ÿcarry
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿidÿvariableÿ=ÿid

    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿAnalysisÿofÿvarianceÿ(ANOVA)ÿforÿaÿ2x2ÿcrossoverÿstudy
    ÿÿÿÿÿSourceÿofÿVariationÿÿ|ÿPartialÿSSÿÿÿdfÿÿÿÿÿÿÿÿMSÿÿÿÿÿÿÿÿÿÿFÿÿÿÿÿProbÿ>ÿFÿ
    ÿÿÿÿ----------------------+--------------------------------------------------
    ÿÿÿÿÿIntersubjectsÿÿÿÿÿÿÿÿ|
    ÿÿÿÿÿÿÿÿÿÿSequenceÿeffectÿ|ÿÿÿÿÿ378.04ÿÿÿÿ1ÿÿÿÿÿÿ378.04ÿÿÿÿÿÿ0.29ÿÿÿÿÿÿ0.5961
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿResidualsÿ|ÿÿÿ17991.26ÿÿÿ14ÿÿÿÿÿ1285.09ÿÿÿÿÿÿ1.40ÿÿÿÿÿÿ0.2691
    ÿÿÿÿ----------------------+--------------------------------------------------
    ÿÿÿÿÿIntrasubjectsÿÿÿÿÿÿÿÿ|
    ÿÿÿÿÿÿÿÿÿTreatmentÿeffectÿ|ÿÿÿÿÿ455.04ÿÿÿÿ1ÿÿÿÿÿÿ455.04ÿÿÿÿÿÿ0.50ÿÿÿÿÿÿ0.4931
    ÿÿÿÿÿÿÿÿÿÿÿÿPeriodÿeffectÿ|ÿÿÿÿÿ419.47ÿÿÿÿ1ÿÿÿÿÿÿ419.47ÿÿÿÿÿÿ0.46ÿÿÿÿÿÿ0.5102
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿResidualsÿ|ÿÿÿ12860.78ÿÿÿ14ÿÿÿÿÿÿ918.63
    ÿÿÿÿ----------------------+--------------------------------------------------
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿTotalÿ|ÿÿÿ32104.59ÿÿÿ31

    ÿÿÿÿOmnibusÿmeasureÿofÿseparabilityÿofÿtreatmentÿandÿcarryoverÿ=ÿÿÿ29.2893%

    .ÿ
    .ÿdisplayÿinÿsmclÿasÿtextÿe(cmdline)
    anovaÿoutcomeÿ__000001/id|__000001ÿtreatÿperiodÿifÿ__000003,ÿ

    .ÿ
    .ÿ*
    .ÿ*ÿBeginÿhere
    .ÿ*
    .ÿanovaÿoutcomeÿsequenceÿ/ÿid|sequenceÿtreatÿperiod

    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿNumberÿofÿobsÿ=ÿÿÿÿÿÿÿÿÿ32ÿÿÿÿR-squaredÿÿÿÿÿ=ÿÿ0.5994
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿRootÿMSEÿÿÿÿÿÿ=ÿÿÿÿ30.3089ÿÿÿÿAdjÿR-squaredÿ=ÿÿ0.1130

    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿSourceÿ|ÿPartialÿSSÿÿÿÿÿÿÿÿÿdfÿÿÿÿÿÿÿÿÿMSÿÿÿÿÿÿÿÿFÿÿÿÿProb>F
    ÿÿÿÿÿÿÿÿÿÿÿÿÿ------------+----------------------------------------------------
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿModelÿ|ÿÿ19243.812ÿÿÿÿÿÿÿÿÿ17ÿÿÿ1131.9889ÿÿÿÿÿÿ1.23ÿÿ0.3504
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ|
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿsequenceÿ|ÿÿ378.04323ÿÿÿÿÿÿÿÿÿÿ1ÿÿÿ378.04323ÿÿÿÿÿÿ0.29ÿÿ0.5961
    ÿÿÿÿÿÿÿÿÿÿÿÿÿid|sequenceÿ|ÿÿ17991.264ÿÿÿÿÿÿÿÿÿ14ÿÿÿ1285.0903ÿÿ
    ÿÿÿÿÿÿÿÿÿÿÿÿÿ------------+----------------------------------------------------
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿtreatÿ|ÿÿ455.03758ÿÿÿÿÿÿÿÿÿÿ1ÿÿÿ455.03758ÿÿÿÿÿÿ0.50ÿÿ0.4931
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿperiodÿ|ÿÿ419.46755ÿÿÿÿÿÿÿÿÿÿ1ÿÿÿ419.46755ÿÿÿÿÿÿ0.46ÿÿ0.5102
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ|
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿResidualÿ|ÿÿ12860.782ÿÿÿÿÿÿÿÿÿ14ÿÿÿ918.62725ÿÿ
    ÿÿÿÿÿÿÿÿÿÿÿÿÿ------------+----------------------------------------------------
    ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿTotalÿ|ÿÿ32104.594ÿÿÿÿÿÿÿÿÿ31ÿÿÿÿ1035.632ÿÿ

    .ÿmarginsÿtreat

    PredictiveÿmarginsÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿNumberÿofÿobsÿÿÿÿÿ=ÿÿÿÿÿÿÿÿÿ32

    Expressionÿÿÿ:ÿLinearÿprediction,ÿpredict()

    ------------------------------------------------------------------------------
    ÿÿÿÿÿÿÿÿÿÿÿÿÿ|ÿÿÿÿÿÿÿÿÿÿÿÿDelta-method
    ÿÿÿÿÿÿÿÿÿÿÿÿÿ|ÿÿÿÿÿMarginÿÿÿStd.ÿErr.ÿÿÿÿÿÿtÿÿÿÿP>|t|ÿÿÿÿÿ[95%ÿConf.ÿInterval]
    -------------+----------------------------------------------------------------
    ÿÿÿÿÿÿÿtreatÿ|
    ÿÿÿÿÿÿÿÿÿÿRÿÿ|ÿÿÿ151.4779ÿÿÿ7.577216ÿÿÿÿ19.99ÿÿÿ0.000ÿÿÿÿÿ135.2264ÿÿÿÿ167.7294
    ÿÿÿÿÿÿÿÿÿÿTÿÿ|ÿÿÿ159.0197ÿÿÿ7.577216ÿÿÿÿ20.99ÿÿÿ0.000ÿÿÿÿÿ142.7682ÿÿÿÿ175.2713
    ------------------------------------------------------------------------------

    .ÿ
    .ÿexit

    endÿofÿdo-file


    .

    Comment


    • #3
      Hi Joseph,

      Thank you very much for your prompt response. That was very helpful.
      Have a nice weekend,

      Dimi

      Comment


      • #4
        Hi Joseph,

        Please, one more clarification. By using the command:

        . margins treat

        without any other option such as asbalanced, the results I will get are the least squares means (lsmeans in SAS). I am right?

        Thanks a lot in advance,

        Dimi

        Comment

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