Environmental risk factors and drinking outcomes were typically examined using the same type of assessment instrument (e.g., self-report questionnaire or interview), and some of the observed covariance may be attributable to method variance rather than covariance of the underlying constructs. This is particularly problematic given the evidence that heritability estimates can vary with assessment method (MacGregor, Cornes, Martin, & Visscher, 2006). Researchers can increase validity and statistical power by more accurately measuring the timing of environmental exposures and drinking behaviors using multiple assessment methods or multiple informants, mindful of the direction of effects.
