Frequency of Youth E-Cigarette and Tobacco Use Patterns in the United States: Measurement Precision Is Critical to Inform Public Health.

INTRODUCTION: E-cigarette use occurs with tobacco product use in youth. METHODS: Using the 2014 National Youth Tobacco Survey (NYTS), we examined past 30-day frequency of cigarette, cigar, smokeless, and e-cigarette use in the context of past 30-day and ever tobacco product use in US middle and high school students (N = 22 007). Frequency of product-specific use was examined by exclusive versus concurrent use with another product in the past 30 days (poly-use). RESULTS: In 2014, the majority (83%) of US middle and high school students had not used tobacco or e-cigarettes in the past 30 days. In the 9.3% of youth reporting any past 30-day e-cigarette use, 63% also reported using a tobacco product; among the 3.3% past 30-day exclusive e-cigarette users, about two-thirds (2.1%) had ever used combustible or non-combustible tobacco products and one-third (1.2%) had not. Few never tobacco users had used e-cigarettes on 10 or more days in the past month (absolute percent < 0.1%). Among past 30-day cigarette and smokeless users, the two highest frequency categories were 1-2 days and daily use; among past 30-day e-cigarette and cigar users, prevalence decreased with increasing frequency of use. The majority of past 30-day cigarette, cigar, smokeless, and e-cigarette users reported poly-use. CONCLUSIONS: Prevalence estimates for a single product mask the complex patterns of frequency, temporality, and poly-use in youth. Two-thirds of past 30-day exclusive e-cigarette users have ever used tobacco. Poly-use is the dominant pattern of tobacco and e-cigarette use among US middle and high school students. IMPLICATIONS: Our study highlights the complexity of tobacco use patterns in US middle and high school students. Future studies addressing the full public health impact of movement into or out of combustible tobacco use will require longitudinal data with appropriate measures of tobacco and e-cigarette product-specific use (eg, frequency and intensity), as well as adequate sample size and a sufficient number of waves to determine how use of individual products, like e-cigarettes, impact progression into or out of more stable patterns of tobacco and e-cigarette use.