Nested within this population study was an intensive assessment targeting 1035 families, comprising about 40% of all twins, most (72.3%; 748 families) selected at random. About one-quarter of the families (27.7%; 287 families) were assumed to be at elevated familial risk for alcoholism, based on one or both parents' scores on an 11-item lifetime version of the Malmö-modified Michigan Alcoholism Screening Test (Seppä et al., 1990). Details about these families have been described earlier (Rose et al., 2001).
