Table 4.

Spearman correlations between duration or frequency of use and product use behavior for e-cigarettes and tobacco cigarettes.

		E-cigarettes		Tobacco cigarettes
		Use duration (years)	Days vaped/week (past 30d)	Use duration (years)	Days smoked/week (past 30d)
E-cigarettes	Use duration (years)	-	0.02	0.19***	0.02
	Days vaped/week (past 30d)	0.02	-	−0.03	−0.03
	Times used/day	0.03	0.48***	0.01	−0.10
	Estimated puffs/bout	0.02	0.05	−0.06	0.01
	Modified FTCD score	0.04*	0.23***	0.01	−0.11*
Tobacco cigarettes	Use duration (years)	0.19***	−0.03	-	0.34***
	Days smoked/week (past 30d)	0.02	−0.03	0.34***	-
	Cigarettes/day	0.01	−0.12*	0.52***	0.64***
	Cigarettes/day prior to e-cigarettes	0.01	0.11*	0.53***	0.41***
	Cigarettes/day change score	−0.01	−0.37***	−0.13*	0.11*
	Days smoked/week prior to e-cigarettes	0.05*	0.19***	0.36***	0.62***
	Days smoked/week change score	0.02	−0.22***	0.03	0.52***
	Estimated puffs/bout	−0.02	−0.01	0.20***	0.20***
	FTCD score	0.02	0.05*	0.43***	0.43***

Note FTCD = Fagerström Test for Cigarette Dependence. Change score = current use minus use prior to e-cigarette initiation.

^*p < .05;

^**p < .01;

^***p < .001