Inconsistent Reporting of Cigarette Smoking Among European High-School Students: Prevalence and Impact on Daily Use Estimates Across 48 Countries and Regions

BACKGROUND: Inconsistent reporting can bias epidemiological findings, including prevalence estimates and associations, yet it is seldom examined in cross-sectional tobacco research. METHODS: Using data from the European School Survey Project on Alcohol and Other Drugs (ESPAD; 1995-2015), this study analyzed data from 553,951 adolescents aged 15-16 from 48 European countries and regions. Inconsistent reporting of cigarette smoking was identified through logical contradictions across lifetime use, past-month use, and smoking onset items. This study estimated the prevalence of inconsistent reporting and assessed its impact on daily use among past 30-day smokers. RESULTS: Overall, 6.3% of participants provided at least one inconsistent response, with substantial cross-territorial variation (2.4%-16.5%). Adjusting for inconsistent reporting systematically reduced the prevalence of daily users among past 30-day smokers, with an overall relative change of -4.1% and a maximum reduction of -20.5% observed in Kosovo. CONCLUSION: Inconsistent reporting of adolescent cigarette use is common and meaningfully affects prevalence estimates, though its impact does not scale linearly with its frequency. Routine assessment and handling of inconsistent responses should be integrated into tobacco epidemiology to improve data validity and policy relevance.