Description of Test: This rating assesses the similarity of the twins on ten physical characteristics of the head. (Nichols R. C., & Bilbro, W. C. (1966). The diagnosis of twin zygosity. Acta Geneticae Medicae et Gemellologiae, 16, 265-275.) NOTE: No formal description of the Zygosity Rating procedure exists in the MALTS procedure document. Individual examiners completed the zygosity form during the LAB visit, without comparing impressions with their co-examiner.  To see the form on which the data was recorded, click to see form.

Reference: Nichols R. C., & Bilbro, W. C. (1966). The diagnosis of twin zygosity. Acta Geneticae Medicae et Gemellologiae, 16, 265-275.

Articles: The following articles cite or use data from the LAB Zygosity Rating procedure:

Still to be added

Variable Names:  Variable names from this database have the prefix V1LZYG. The data set has 343 families and 53 variables. Data were collected as part of a visit to the MALTS laboratory at the Institute for Behavioral Genetics in Boulder, Colorado of 14 month old twins. The variables include: Rater ID and 25 ratings for each of the two raters and a comment field.   NOTE: This data set was originally organized by FAMILY, not individual twin. Data has been duplicated for the individual twin-level file.    Move there to move to the complete list of variable names from this database.

Cleaning:  The data have been examined to ensure that the values of the variables are within range.

Composites:  There are currently no composite variables defined from the LAB Zygosity Rating procedure.