2.4. Statistical analysis

Overall unit sales and share of unit sales of concept flavor e-cigarettes by nicotine concentration level (NCL) as indicated on the packaging, flavor type, and device type were calculated as a proportion of total concept flavor e-cigarette unit sales. Average monthly percentage change (AMPC) in unit sales and 95 % CIs were calculated using Joinpoint version 4.9.1.0 (National Cancer Institute), a segmented regression analysis application. Based on the approach adopted in prior research, (Ali et al., 2022) time points detected during the analysis of concept flavor e-cigarette sales overall (i.e., across all years) were used to assess whether trends by flavor type, device type and NCL varied significantly during these time periods. Supplemental Fig. 1 demonstrates trends in concept flavor e-cigarette sales as a proportion of overall e-cigarette unit sales in the US during 2019–2020. Supplemental Fig. 2 demonstrates proportion of concept flavor e-cigarette vs. non-concept flavor e-cigarette unit sales during 2019–2022. Fig. 1, Fig. 2, Fig. 3 depict trends in unit sales overall, by nicotine concentration levels, and flavor type; and Fig. 3 Supplemental section by device type respectively. Table 1 includes data related to AMPC or MPC and corresponding 95 % Confidence Intervals, and monthly percentage unit shares. Unit sales for each time period are reported in Supplemental Table 2. Statistical significance was defined as p < 0.05.

Overall sales of concept flavor e-cigarettes in the US: August 2019-April 2022.

Trends in unit sales of concept flavor e-cigarettes by nicotine concentration in the US: August 2019-April 2022. Notes: Concept flavor e-cigarette products were categorized in terms of 0%-2.0%, 2.1%-4.0%, greater than 4.1% and Unknown nicotine concentration levels. Each bar in the figure represents aggregate sales in a 4-week interval.

Trends in unit sales of concept flavor e-cigarettes by flavor type in the US: August 2019-April 2022. Notes: Concept flavor e-cigarette product flavors were categorized in terms of tobacco, fruity, mint, menthol, and other flavors. Each bar in the figure represents aggregate sales in a 4-week interval.

Concept flavor e-cigarettes unit sales average monthly percent change and unit share for each time period: August 2019-April 2022.

*Indicates that AMPC is significantly different from zero at alpha = 0.05.