Stata 15 help for margins_contrast

Title

[R] margins, contrast -- Contrasts of margins

Syntax

margins [marginlist] [if] [in] [weight] [, contrast margins_options]

margins [marginlist] [if] [in] [weight] [, contrast(suboptions) margins_options]

where marginlist is a list of factor variables or interactions that appear in the current estimation results. The variables may be typed with or without contrast operators, and you may use any factor-variable syntax:

. margins sex##group, contrast

. margins sex##g.group, contrast

. margins sex@group, contrast

See the operators (op.) table in [R] contrast for the list of contrast operators. Contrast operators may also be specified on the variables in margins's over() and within() options to perform contrasts across the levels of those variables.

suboptions Description ------------------------------------------------------------------------- Contrast overall add a joint hypothesis test for all specified contrasts lincom treat user-defined contrasts as linear combinations predict(op[._predict]) apply the op. contrast operator to the groups defined by multiple predict() options atcontrast(op[._at]) apply the op. contrast operator to the groups defined by at() predictjoint test jointly across all groups defined by multiple predict() options atjoint test jointly across all groups defined by at() overjoint test jointly across all levels of the unoperated over() variables withinjoint test jointly across all levels of the unoperated within() variables marginswithin perform contrasts within the levels of the unoperated terms in marginlist

cieffects show effects table with confidence intervals pveffects show effects table with p-values effects show effects table with confidence intervals and p-values nowald suppress table of Wald tests noatlevels report only the overall Wald test for terms that use the within @ or nested | operator nosvyadjust compute unadjusted Wald tests for survey results -------------------------------------------------------------------------

fweights, aweights, iweights, and pweights are allowed; see weight.

Menu

Statistics > Postestimation

Description

margins with the contrast option or with contrast operators performs contrasts of margins. This extends the capabilities of contrast to any of the nonlinear responses, predictive margins, or other margins that can be estimated by margins.

Suboptions

+----------+ ----+ Contrast +---------------------------------------------------------

overall specifies that a joint hypothesis test over all terms be performed.

lincom specifies that user-defined contrasts be treated as linear combinations. The default is to require that all user-defined contrasts sum to zero. (Summing to zero is part of the definition of a contrast.)

predict(op._predict) specifies that the op. contrast operator be applied to the groups defined by multiple specifications of margins's predict() option. The default behavior, by comparison, is to perform tests and contrasts within these groups.

atcontrast(op._at) specifies that the op. contrast operator be applied to the groups defined by the at() option(s). The default behavior, by comparison, is to perform tests and contrasts within the groups defined by the at() option(s).

See example 6 in Remarks and examples of [R] margins, contrast.

predictjoint specifies that joint tests be performed across all groups defined by multiple specifications of margins's predict() option. The default behavior, by comparison, is to perform contrasts and tests within each group.

atjoint specifies that joint tests be performed across all groups defined by the at() option. The default behavior, by comparison, is to perform contrasts and tests within each group.

See example 5 in Remarks and examples of [R] margins, contrast.

overjoint specifies how unoperated variables in the over() option are treated.

Each variable in the over() option may be specified either with or without a contrast operator. For contrast-operated variables, the specified contrast comparisons are always performed.

overjoint specifies that joint tests be performed across all levels of the unoperated variables. The default behavior, by comparison, is to perform contrasts and tests within each combination of levels of the unoperated variables.

See example 3 in Remarks and examples in [R] margins, contrast.

withinjoint specifies how unoperated variables in the within() option are treated.

Each variable in the within() option may be specified either with or without a contrast operator. For contrast-operated variables, the specified contrast comparisons are always performed.

withinjoint specifies that joint tests be performed across all levels of the unoperated variables. The default behavior, by comparison, is to perform contrasts and tests within each combination of levels of the unoperated variables.

marginswithin specifies how unoperated variables in marginlist are treated.

Each variable in marginlist may be specified either with or without a contrast operator. For contrast-operated variables, the specified contrast comparisons are always performed.

marginswithin specifies that contrasts and tests be performed within each combination of levels of the unoperated variables. The default behavior, by comparison, is to perform joint tests across all levels of the unoperated variables.

See example 4 in Remarks and examples in [R] margins, contrast.

cieffects specifies that a table containing a confidence interval for each individual contrast be reported.

pveffects specifies that a table containing a p-value for each individual contrast be reported.

effects specifies that a single table containing a confidence interval and p-value for each individual contrast be reported.

nowald suppresses the table of Wald tests.

noatlevels indicates that only the overall Wald test be reported for each term containing within or nested (@ or |) operators.

nosvyadjust is for use with svy estimation commands. It specifies that the Wald test be carried out without the default adjustment for the design degrees of freedom. That is to say the test is carried out as W/k ~ F(k,d) rather than as (d-k+1)W/(kd) ~ F(k,d-k+1), where k is the dimension of the test and d is the total number of sampled PSUs minus the total number of strata.

Examples

These examples are intended for quick reference. For a conceptual overview of margins, contrast and examples with discussion, see Remarks and examples in [R] margins, contrast.

. webuse margex . logistic outcome treatment##group age c.age#c.age treatment#c.age . margins, dydx(treatment) . margins r.treatment . margins treatment#group, contrast(wald) . margins treatment@group, contrast(wald) . margins treatment, over(group) contrast(wald overjoint) . margins treatment, over(group) contrast(wald)

Stored results

margins, contrast stores the following additional results in r():

Scalars r(k_terms) number of terms participating in contrasts

Macros r(cmd) contrast r(cmd2) margins r(overall) overall or empty

Matrices r(L) matrix of contrasts applied to the margins r(chi2) vector of chi-squared statistics r(p) vector of p-values corresponding to r(chi2) r(df) vector of degrees of freedom corresponding to r(p)

margins, contrast with the post option also stores the following additional results in e():

Scalars e(k_terms) number of terms participating in contrasts

Macros e(cmd) contrast e(cmd2) margins e(overall) overall or empty

Matrices e(L) matrix of contrasts applied to the margins e(chi2) vector of chi-squared statistics e(p) vector of p-values corresponding to e(chi2) e(df) vector of degrees of freedom corresponding to e(p)


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