| Class | Analysis and data manipulation command |
| Name | twin |
| Arguments | <trait> [<zygosity_score> even | odd | (>|>=|<|<=|==|^= <threshold>)] |
Calculate, and test for equality of, MZ and DZ twin correlations or concordances. If a zygosity indicator is not specified, the indicator declared by the set twin command is used to divide siblings into MZ twins and non-MZ full siblings (DZ twins and "singletons"). If a zygosity indicator is specified, then this is used to define three groups: MZ twins (indicator expression TRUE or greater than zero), DZ twins (indicator FALSE or equal to zero), and nontwin siblings (indicator value is missing). The Z test for equality of the Pearson correlation coefficients is actually the likelihood ratio test [Brandner 1933].
Example:
>> twin ace zyg == 1
------------------------------------------------------------
Classical twin analysis of "ace"
------------------------------------------------------------
Zygosity Group N Pairs Mean Std Dev Correlation (95%CI)
-------------- ------- ------------ --------- -------------------------
MZ twins 103 126.7573 48.6038 0.661 ( 0.536 -- 0.757)
DZ twins 123 130.6057 51.5562 0.466 ( 0.315 -- 0.594)
MZ Female 73 121.5068 48.2225 0.675 ( 0.527 -- 0.783)
MZ Male 30 139.5333 47.5279 0.589 ( 0.527 -- 0.783)
DZ Female 51 130.0784 48.9865 0.414 ( 0.157 -- 0.619)
DZ Male 25 148.7200 49.2035 0.648 ( 0.340 -- 0.830)
DZ Female-Male 47 113.4468, 48.2790, 0.423 ( 0.155 -- 0.633)
129.6383 57.6136
Hypothesis Z-statistic P-value
--------------- ----------- -------
r(MZF) = r(MZM) 0.66 0.5099 .
r(DZF) = r(DZM) 1.35 0.1772 .
r(MZ) = r(DZ) 2.16 0.0153 +
Falconer style estimates of heritability
Heritability h2= 0.390
Domesticity c2= 0.271
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