Reliably separating identical from fraternal twins.

Area of Science:

• Psychology
• Behavioral Genetics
• Twin Studies

Background:

• Blood typing is the gold standard for determining twin zygosity in research.
• Practical challenges like cost and specimen collection limit its use in large-scale studies, especially with children.

Purpose of the Study:

• To develop and validate a parent-completed questionnaire for assessing twin zygosity in young children.
• To provide a cost-effective and practical alternative to blood typing for twin research.

Main Methods:

• A questionnaire was designed to assess zygosity based on parental ratings of twin likeness and instances of mistaken identity.
• The questionnaire's validity was tested against blood typing results.
• Test-retest reliability was assessed by having mothers of same-sex twins complete the questionnaire twice.

Main Results:

• The questionnaire demonstrated high test-retest reliability, with mothers showing strong agreement across two separate administrations.
• Parental perceptions of monozygotic (identical) and dizygotic (fraternal) twins differed significantly.
• The study validated the questionnaire as a reliable tool for zygosity assessment.

Conclusions:

• A parent-completed questionnaire is a valid and reliable method for determining twin zygosity in psychological research.
• This method simplifies data collection for epidemiological studies involving twins.
• Parental perceptions of zygosity may reflect environmental differences, challenging assumptions in heritability estimates.