Measurements: Data were collected on demographics, e-cigarette advertising exposure measured using the cued-recall method and recent (past 30-day) cigarette and e-cigarette use.
Findings:The average trajectory for e-cigarette advertising exposure over time was significant and upward [M slope = 0.18 (0.14-0.22), P < 0.0001]. However, average trajectories for e-cigarette [M slope = −0.08 (−0.18 to 0.02), P = 0.09] and cigarette [M slope = −0.14 (−0.30 to 0.02), P = 0.07] use were not. There were significant differences in individual level trajectories across participants for advertising exposure [σ 2 = 0.12 (0.10-0.14), P < 0.0001], e-cigarette use [σ 2 = 0.22 (0.14-0.30), and cigarette smoking (σ 2 = 0.17 [0.09-0.25], P < 0.0001). Individuals with an increasing rate of advertising exposure showed an increasing rate of e-cigarette use [B = 0.63 (0.36-0.90), P < 0.0001). Neither initial level of, nor rate of change in, advertising exposure was significantly associated with cigarette smoking growth factors (P > 0.05). Higher initial level of e-cigarette use was associated with higher initial level of cigarette smoking [B = 0.89 (0.69-1.09), P < 0.0001] but decreased rate of cigarette smoking over time [B = −0.12 (−0.20 to -0.04) P = 0.003]. Rate of change in e-cigarette use was not associated with the rate of change in cigarette smoking (P > 0.05).