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help for ^symmetry^                                               (STB-40: sg74)
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Symmetry and Marginal Homogeneity test/ TDT test
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^symmetry^ var_cases var_controls [weight] [^if^ exp] [^in^ range]
 				  [^,^ ^not^able ^con^trib ^ex^act ^mh^]

^symmi^ #11 #12 [...]^\^ #21 #22 [...] [^\^...] [^if^ exp] [^in^ range]
				  [^,^ ^not^able ^con^trib ^ex^act ^mh^]

^fweight^s are allowed; see help @weights@.

Description
-----------

^symmetry^ performs asymptotic symmetry and marginal homogeneity tests and
exact symmetry test on NxN tables where there is a 1-to-1 matching of cases
and controls (non-independence). The test is used to analyze matched-pair
case-control data with multiple discrete levels of the outcome variable. In
genetics, the test is known as the Transmission/Disequilibrium test (TDT) and
is used to test the association between transmitted and non-transmitted
parental marker alleles to an affected child. In the case of 2x2 tables the
asymptotic test statistics reduce to the McNemar test statistic and the exact
symmetry test produces an exact McNemar test.

^symmetry^ expects the data to be in wide format.  That is, each observation
contains the two matched case and control values in variables var_cases and
var_controls.  Variables can be numeric or string.

^symmi^ performs the symmetry and marginal homogeneity tests using the values
specified on the command line; rows are separated by ^\^.  The same options as
for the ^symmetry^ command are available for the immediate form.


Options
-------

^notable^ suppresses the output of the contingency table. 

^contrib^ reports the contribution of each off-diagonal cell-pair to the
    overall symmetry chi-squared.

^exact^ performs an exact test of table symmetry. CAUTION:  the exact test
    requires substantial amounts of time and memory for large tables.

^mh^ performs two marginal homogeneity tests that do not require the
    inversion of the variance-covariance matrix.

Examples
--------

 . ^symmetry cases controls^
 . ^symmetry cases controls, not^
 . ^symmetry cases controls, con mh^
 . ^symmetry cases controls, mh ex^
 . ^symmetry cases controls, ex  con^

Author
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      Mario Cleves 
      Stata Corporation
      email: mcleves@@stata.com


Also see
--------

    STB:  STB-40 sg74
On-line:  help for @epitab@