Class | Data Declaration command |
Name | set twin |
Arguments | <quantitative trait> [merlin] |
Declares which variable identifies twins. All individuals within a pedigree with the same nonmissing value of this variable are taken to be part of the same twin sibship (twin pair or higher order multiple). Different values indicate different twin pairs within the same family.
If the merlin coding has been specified, odd numbers indicate MZ twins, and even numbers DZ twins. For the default coding, nonzero values indicate MZ twins, and DZ twins can be indicated using a zero value for the indicator. If a zygosity indicator was declared in a MERLIN data file (see read locus), this automatically toggles use of the MERLIN encoding.
The zygosity indicator variable must be declared as a quantitative trait using the set locus command; this can be before or after the set twin statement. The zygosity indicator variable can be changed at any time.
This information is used to write out MZ twin indicators to the pedigree files used by MENDEL, MERLIN and SOLAR, to test for marker inconsistencies, and carry out classical twin analyses.
Example:
>> set locus mzdz qua >> set twin mzdz NOTE: The phenotype "mzdz" indicates monozygotic (twin) sibships.
See also:
mztwin | MZ pair genotype discordance | drop one member |
twin | Classical twin analysis |
kendalltau | Twin survival analysis |
<< (set sex) | Up to index | >> (set liability) |