Self-reported drug use: is it reliable?
Studies of illicit drug use often rely on people's self-reported use. Although the collection of self-report measures can provide a convenient, relatively inexpensive, and non-invasive method for obtaining information about illicit drug use, concerns about the reliability of such reports are often raised. Reasons proposed for their potential inaccuracy relate to stigma, negative consequences of disclosing use, poor recall on the participant's part, and the variable content of illicit drugs.
Biological samples are often used as an adjunct or substitute measure of drug use. The detection of biochemical markers of illicit drugs in biological samples (such as urine and saliva) can provide a more 'objective' measure of drug use. However, biological testing results are not perfect and discrepancies, when compared with self-reporting, can only sometimes be attributed to misreporting of use by a person. Understanding how the agreement between self-report and biologically measured illicit drug use varies according to different factors (e.g., type of drug, biological sample, settings) will help inform the reliability of illicit drug use measures in real-world, research, and clinical settings.
In a study recently published in Addiction (titled ‘Agreement between self-reported illicit drug use and biological samples: A systematic review and meta-analysis’), we comprehensively examine the evidence for agreement between self-reported and biologically measured illicit drug use across all major illicit drug classes and biological indicators and the extent to which this varies across the populations and settings in which these measures are collected.
Key findings of our recent study are outlined below:
- Overall agreement between self-reported drug use and biological measures was high. However, there was substantial between-study variability in other summary estimates (e.g., sensitivity, specificity, and predictive values).
- Longer timeframes of self-reported drug use tended to provide better agreement. This suggests individuals may be more comfortable reporting drug use that could be perceived as being more temporally distant to the time of self-reporting.
- Sensitivity was higher among cohorts with a high proportion of people who use drugs. This is consistent with what one might expect from studies recruiting people based on their dependence or high drug use, where prior drug use is already acknowledged as a condition of study participation.
- Agreement tended to be higher in trials and situations with no consequences. This reinforces the importance of conducting research that puts in place strategies to ensure individuals feel confident they will not experience stigma or negative consequences because of reporting use.
- Half of all studies used methods for testing the biological samples that are considered at high risk of bias. This highlights the importance of considering the suitability of biological testing methods for particular applications in relation to their limitations.
So, what are the main takeaways from this study? While there are limitations associated with self-report and biological testing to measure illicit drug use, the overall agreement between the two methods is high, suggesting both provide accurate measures of illicit drug use. Recommended methods of biological testing are more likely to provide reliable measures of recent use if there are problems with self-disclosure.