Based on NHANES questionnaire data on recent tobacco use (NHANES dataset: SMQRTU), NHANES participants were excluded from analysis if they reported using smokeless tobacco or nicotine replacement therapy, as indicated by responding “yes” to question SMQ680 (tobacco or nicotine use within 5 days prior to NHANES physical examination) and “yes” to at least one of SMQ690D – SMQ690F (smokeless tobacco and nicotine delivery products). These participants were excluded because smokeless tobacco and nicotine replacement therapy are alternative sources of nicotine (and hence its metabolite cotinine), but whose use does not involve combustion. The remaining participants were then identified as exclusive users of combusted tobacco products (named “exclusive combusted tobacco users” or “exclusive smokers” in this report) if they responded “yes” to SMQ680 and “yes” to at least one of SMQ690A – SMQ690C (cigarettes, pipes, cigars). Participants were identified as non-users of tobacco products if they answered “no” to SMQ680 or were both missing a response to SMQ680 and had serum cotinine ≤10 ng/mL. The serum cotinine threshold of >10 ng/mL has been identified as consistent with active use of combusted tobacco products, and was used to stratify self-identified exclusive smokers and non-users in statistical analyses reported herein.15 (link) Participants were excluded from analysis for use of smokeless tobacco and nicotine replacement therapy (N=244), for missing serum cotinine data (N=3), or for missing data for other variables used in regression models (N=1,023). This attrition left 6,730 study participants eligible for statistical analysis.