title: Developing a quantitative measure of alcohol consumption for genomic studies on prospective cohorts.
abstract: OBJECTIVE
  The purpose of this study was to develop a quantitative measure of alcohol consumption for gene-mapping studies.
  
  
  METHODS
  Using a sample of 3,787 young-adult twin women and an independent sample of 489 men and women from a college drinking study, we developed an alcohol-consumption factor score indexed by (1) maximum typical consumption (log-transformed quantity frequency [LQNTFRQ]), (2) maximum drinks in a 24-hours period (LMAXALC), (3) frequency of drinking five or more drinks per day (FIVE), and (4) frequency of drinking to intoxication (INTOX). We tested (1) for factorial and psychometric equivalence across samples and genders; (2) for construct validity and its equivalence, across samples and genders, using measures of tobacco and cannabis use and family history of alcoholism; and (3) to determine the heritability of the alcohol-consumption factor score using a genetic psychometric model.
  
  
  RESULTS
  A single-factor model fit well with factor loadings ranging from .60 to .90. With rare exception, we found support for measurement invariance across the two samples and across genders. Measures of nicotine and cannabis use as well as family history of alcoholism were associated, to a similar extent across samples and genders, with the underlying alcohol-consumption factor. Psychometric twin modeling revealed that each of the alcohol-consumption measures (h2=34%-47%) and the underlying factor score (h2=50%) were heritable, with the remainder of the variance attributable to individual-specific environmental factors. This moderately heritable alcohol-consumption factor also accounted for a majority of the genetic variance in LQNTFRQ, LMAXALC, FIVE, and INTOX.
  
  
  CONCLUSIONS
  Quantitative measures of alcohol consumption with the favorable attributes of measurement invariance, construct validity, and moderate heritability can greatly enhance future gene-mapping efforts, supplementing information afforded by conventional diagnostic measures of alcohol abuse/dependence.
authors.affiliation: Department of Psychiatry, Washington University School of Medicine, 660 S. Euclid Avenue, Box 8134, St. Louis, Missouri 63110, USA. arpana@wustl.edu
authors.forename: Arpana
authors.initials: A
authors.lastname: Agrawal
authors.forename: Julia D
authors.initials: JD
authors.lastname: Grant
authors.forename: Andrew
authors.initials: A
authors.lastname: Littlefield
authors.forename: Mary
authors.initials: M
authors.lastname: Waldron
authors.forename: Michele L
authors.initials: ML
authors.lastname: Pergadia
authors.forename: Michael T
authors.initials: MT
authors.lastname: Lynskey
authors.forename: Pamela A F
authors.initials: PA
authors.lastname: Madden
authors.forename: Alexandre
authors.initials: A
authors.lastname: Todorov
authors.forename: Timothy
authors.initials: T
authors.lastname: Trull
authors.forename: Kathleen K
authors.initials: KK
authors.lastname: Bucholz
authors.forename: Richard D
authors.initials: RD
authors.lastname: Todd
authors.forename: Kenneth
authors.initials: K
authors.lastname: Sher
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Heath
mesh_terms: D000428:Alcohol Drinking / Q000235:genetics*; D015331:Cohort Studies; D005260:Female; D020022:Genetic Predisposition to Disease; D023281:Genomics / Q000379:methods*; D006801:Humans; D008297:Male; D010641:Phenotype; D011594:Psychometrics; D012307:Risk Factors; D018433:Twin Studies as Topic; D055815:Young Adult