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. Author manuscript; available in PMC: 2018 Jul 1.
Published in final edited form as: Prev Med. 2017 Jul;100:279–284. doi: 10.1016/j.ypmed.2017.03.023

Table 2.

Negative binomial model of e-cigarette stability and total cigarettes smoked over time.

Predictor Coefficient Std. Error z p-value IRR (95% ci)
Propensity score 0.03 0.02 1.60 .109 1.03 (0.99, 1.07)
Assessment days 0.10 0.02 4.74 <.001 1.11 (1.06, 1.16)
Sex -0.26 0.11 -2.35 .019 0.77 (0.62, 0.96)
Student status -0.19 0.12 -1.64 .100 0.83 (0.66, 1.04)
Pre-baseline cigarette frequency 0.62 0.13 4.65 <.001 1.67 (1.32, 2.15)
Pre-baseline e-cigarette frequency 0.02 0.05 0.42 .676 1.02 (0.93, 1.12)
Time 0.21 0.16 1.28 .201 1.23 (0.89, 1.70)
Time2 -0.10 0.04 -2.36 .018 0.91 (0.84, 0.98)
E-cigarette stability 0.16 0.05 3.32 .001 1.18 (1.07, 1.30)