TABLE 2

Descriptive Statistics of Past 30-Day Cigarette and E-Cigarette Use by Wave (N = 808)

VariableWave 1: 2013Wave 2: 2014Wave 3: 2015
Age, mean (SD)15.0 (0.9)15.5 (1.0)16.4 (1.0)
Past-month cigarette use, No. (%)39 (4.8)a44 (5.4)a69 (8.5)b
Past-month e-cigarette use, No. (%)72 (8.9)a97 (12.0)b117 (14.5)b
Days of cigarette use, No. (%)
 1–5 d29 (3.6)a27 (3.3)a38 (4.7)a
 6–10 d2 (0.2)a6 (0.7)a8 (1.0)a
 11–20 d4 (0.5)a7 (0.9)a5 (0.6)a
 21–30 d4 (0.5)a4 (0.5)a18 (2.2)b
Days of e-cigarette use,c No. (%)
 1–5 d42 (5.2)a60 (7.4)a,b69 (8.5)b
 6–10 d16 (2.0)a14 (1.7)a11 (1.4)a
 11–20 d3 (0.4)a12 (1.5)b13 (1.6)b
 21–30 d11 (1.4)a11 (1.4)a24 (3.0)b
  • Frequency values are expressed as the number (and percent) of the total matched longitudinal sample (N = 808).

  • a,b superscripts denote column proportions that differ significantly from one another (p<.05) calculated using a chi-square test.

  • c Number of days of e-cigarette use was recoded into numerical categories to match categorical responses of cigarette use frequency.