How to ask about the use of new psychoactive substances to increase the validity of results in self-report prevalence surveys
Abstract
Introduction and Aims: New psychoactive substances (NPS) represent hundreds of novel compounds. However, the general public might not be familiar with the overarching term NPS.
This can result in both under- and over-reporting of NPS use. Design and Methods: The study analysed the last-year prevalence of NPS use in an online survey conducted across I-TREND project countries (the Czech Republic, the Netherlands and Poland).
Self-reported NPS use was assessed within two types of questions-a generic and a checklist question. We analysed prevalence for each question separately, incorporated the free-text probe 'other' that followed them, and combined the two questions into a conservative and an inclusive estimate.
Results: Including free-text responses to the 'other' categories increased prevalence of NPS use (from 51% to 56% for the checklist question and 25% to 32% for the generic question). Taking an inclusive approach to estimating prevalence (i.e. indicating NPS use in either a generic list or from the checklist) yielded a higher prevalence estimate (60%, 95% confidence interval 58-62%), compared to a more conservative approach in which NPS use had to be affirmed by both questions (27%, 95% confidence interval 26-29%).
Discussion and Conclusions: Generic questions might lead to notably lower estimates of self-reported NPS use in comparison to checklists. However, creating relevant checklists is challenging and lengthy survey instruments have limitations.
Further surveys might benefit from featuring a combination of the strategies used in this study-a single (generic) question involving a number of locally specific NPSs and a free-text 'other' probe.