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. Author manuscript; available in PMC: 2021 Nov 30.
Published in final edited form as: Stat Med. 2020 May 25;39(27):3897–3913. doi: 10.1002/sim.8564

FIGURE 2.

FIGURE 2

Histograms of 5 substance-abuse traits from the Minnesota Center for Twin and Family Research study. For each trait, there were 936 MZ and 478 DZ twin pairs.

Nicotine (NIC): composite measure of nicotine use and dependence; Alcohol Consumption (CON): composite of measures of alcohol use frequency and quantity; Illicit Drugs (DRG): composite of frequency of use of 11 different drug classes and DSM symptoms of drug dependence; Behavioral Disinhibition (BD): composite of measures non-substance use behavioral disinhibition including symptoms of conduct disorder and aggression; Externalizing Factor (EXT): a composite measure of all five previous traits