Zygosity questionnaires have been developed to determine the zygosity of a pair of twins based on their overall similarity (“as alike as two peas in a pod”) and how often they are confused by other people.
TRA has a Peas-in-a-Pod questionnaire with three questions:
The questionnaire is based on research by S Ooki and can accurately determine zygosity for 93% of twin pairs:
- Zygosity Diagnosis of Twins by Questionnaire
- Zygosity Diagnosis in Young Twins by Questionnaire for Twins’ Mothers and Twins’ Self-reports