Testing the validity of national drug surveys: comparison between a general population cohort and household surveys

There are concerns that national population-based estimates of illicit drug use are underestimated. We investigated this by comparing estimates of illicit substance use at age 24 from the Crime Survey for England and Wales (CSEW) with a birth cohort (Avon Longitudinal Study of Parents and Children, ALSPAC) and by comparing the Smoking and Alcohol Toolkit Studies (STS/ATS) to ALSPAC.

Cross-sectional household survey and cross-sectional data from one wave of a longitudinal birth cohort.

England and Wales.

Young adults aged 23-25 reporting on substance use in 2017 to CSEW (n = 1165), ALSPAC (n = 3389) and STS/ATS (n = 950).

Lifetime and past-year illicit drug use, smoking status and hazardous drinking at age 24.

The 2017 CSEW estimate of lifetime illicit drug use was 40.6%, compared with 62.8% in ALSPAC (risk difference % [RD%] = 22.2%; 95% CI = 18.9-25.5%; P ≤ 0.001). The RD in lifetime use between ALSPAC and the CSEW was 23.2% (95% CI = 20.0-26.4%) for cannabis, 16.9% (95% CI = 14.4-19.4%) for powder cocaine and 24.8% (95% CI = 22.6-27.0%) for amphetamine. Past-year drug use was 16.4% in CSEW, compared with 36.7% in ALSPAC (RD% = 20.3%; 95% CI = 17.6-23.0%; P ≤ 0.001). For past-year substance use, the RD between ALSPAC and the CSEW was 15.4% (95% CI = 12.9-17.9%) for cannabis, 14.8% (95% CI = 13.0%-16.6%) for powder cocaine and 15.9% (95% CI = 14.5-17.4%) for amphetamine. Levels of current smoking were similar between STS (27.4%) and ALSPAC (29.4%). Hazardous drinking was substantially higher in ALSPAC (60.3%) than the ATS (32.1%; RD% = 28.2%; 95% CI = 24.8-31.6%; P ≤ 0.001).

The Avon Longitudinal Study of Parents and Children provides one source of validation for measurements of drug use in government household surveys and indicates that illicit drug use may be underestimated in the Crime Survey for England and Wales.