Study Plomin et al. (1993): study US Colorado 1986
- Public
- Same-sex twins, Colorado, United States, followed from 14 to 20 months, 1986-1989
- Sample
- Respondents
- N = 398
- Non Response
- Assessment
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Behavioural observation
At 14 months: observation at home, 2 weeks later observation in laboratory
Correlate
- Authors's Label
- Happiness of twin siblings
- Our Classification
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- Remarks
- monozygotic (MZ) = identical dizygotic (DZ) = non-identical Heritability (h²): the extent to which observed variance in behavior can be attributed to genetic influence: -> doubling the difference between the MZ and DZ correlations, because MZ twins are identical genetically, whereas the genetic correlation for DZ twins is assumed to be +.50 Shared Environment (c²): estimated in the twin method as twin resemblance not explained by heritability: -> twice the DZ correlation minus the MZ correlation (only detects major effects of shared environment) for details of computation see DeFries & Fulker, 1985
- Related specification variables
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- Operationalization
- at 14 and 20 months, twin pairs were first observed at home and 1-3 weeks after that in the laboratory at the Institute for Behavioral Genetics in Boulder during different situations, behavior was videotaped and rated afterwards; the mother was interviewed via phone between the home & lab sessions;
Observed Relation with Happiness
- at 14 months h²=+.15 (ns)
- at 20 months h²=+.10 (ns)
- at 14 months c²=+.00 (ns)
- at 20 months c²=+.17 (ns)
Twin correlations based on each individual's relative change score (20 months - 14 months) using a double entry file.
Shared Environment component: c²=+.00 (ns)
The analysis of continuity is based on cross-twin correlations, that is, the correlation between one twin's score at 14 months and the co-tin's score at 20 months using a double-entry file.
Shared Environment component: c²=+.00 (ns)