Table 2.

Parsimonious Model of Sustained Smoking Abstinence for 6 Months among Participants Assigned to Reward-based Incentives (n = 990)

	OR	95% CI	P Value	AIC Increase*
Fagerström scale			<0.001	17.27
Moderate vs. high dependence	1.11	0.41–3.89
Low to moderate vs. high dependence	1.99	0.73–6.97
Low dependence vs. high dependence	3.20	1.18–11.27
Pre/contemplators vs. preparators	0.55	0.37–0.82	0.004	7.00
Married or living with partner vs. other	1.76	1.21–2.56	0.003	6.90
Natural log of Kirby discounting score (1-unit increase)	0.88	0.81–0.97	0.008	4.78
Base model (design variables)†
Intervention arm
Collaborative vs. individual rewards	1.05	0.74–1.51	0.78
Household income			0.028
$80–100k vs. >100k	1.91	0.78–4.78
$60–80k vs. >100k	2.54	1.17–5.84
$40–60k vs. >100k	1.85	0.89–4.11
$30–40k vs. >100k	2.23	1.01–5.16
$20–30k vs. >100k	1.37	0.64–3.07
$10–20k vs. >100k	0.74	0.29–1.86
$10k vs. >100k	1.08	0.41–2.83
Has benefits vs. no benefits	1.07	0.74–1.55	0.72

Definition of abbreviations: AIC = Akaike information criterion; CI = confidence interval; OR = odds ratio.

^*The stepAIC procedure in R selects the best model based on the combination of variables that achieves the lowest AIC. The AIC for the best-fitting model was 822.35. The AIC shown in the last column indicates the absolute increase in the AIC (from 822.35 in the best model) if that single variable is removed from the full model shown in the table. Variables are presented in order of decreasing changes, indicating less predictive improvement related to that predictor.

^†The AIC for the base model, which included the three design variables (intervention arm, household income, and insurance benefits), was 858.86.