The Self-Report Habit Index: Assessing habitual marijuana, alcohol, e-cigarette, and cigarette use.

Background: Substance use is partially driven by habitual processes that occur automatically in response to environmental cues and may be central to users' identities. This study was designed to validate the Self-Report Habit Index (SRHI) for assessing habitual marijuana, alcohol, cigarette, and e-cigarette use.

Methods: We examined the SRHI's psychometrics in separate samples of adult marijuana (Ns = 189;170), alcohol (Ns = 100;133), cigarette (Ns = 58;371), and e-cigarette (N = 239) users.

Results: A 6-item, single-factor solution evidenced good fit across substances (CFI marijuana/alcohol/cigarettes/e-cigarettes = 0.996/0.997/0.996/0.994, RMSEA = 0.046/0.047/0.067/0.068, SRMR = 0.017/0.017/0.010/0.015) and internal consistency (α = 0.88/0.94/0.95/0.91). The SRHI was scalar invariant for sex and race. However, independent-samples t-tests indicated only that women endorsed stronger habitual e-cigarette use and that men endorsed stronger habitual marijuana use. The SRHI also was scalar invariant by product type in dual-users (cigarettes/e-cigarettes[N = 371]; alcohol/cigarettes [n = 58]), although differences in habit strength only were observed for cigarettes versus e-cigarettes, with dual-users reporting stronger habitual cigarette use. Finally, the SRHI predicted frequency of marijuana, alcohol, cigarette, and e-cigarette use (n [marijuana/alcohol/cigarettes/e-cigarettes] = 0.37/0.48/0.31/0.17) and quantity of alcohol and cigarette use (n = 0.43/0.33).

Conclusions: The SRHI is a psychometrically sound measure of adults' habitual substance use. The SRHI detected mean differences by sex and substance type and predicted the frequency of using each substance. Future research should determine if the SRHI is appropriate for use with other substances or age groups (e.g., adolescents), how it relates to task-based, behavioral measures of habit strength, and the degree to which habit predicts the development or maintenance of addiction.