Changes in	16 year olds n (%)	17 year olds n (%)
Prevalence of e-cigarette ever-use
ESPAD-TFRI 2019	754 (38.8)	279 (37.5)
GUI 2017	1564 (31.3)
SILNE-R-TFRI 2016	148 (31.8)	85 (50.0)
ESPAD-TFRI 2015	252 (24.2)	98 (26.3)
ECIGS-TFRI 2014	77 (25.7)	101 (23.0)
Reasons for trying e-cigarettes
ESPAD-TFRI 2019
To quit smoking Because friends were using it Out of curiosity	16 (3.4) 137 (28.8) 315 (66.3)	14 (5.0) 83 (29.8) 187 (67.0)
ESPAD-TFRI 2015
To quit smoking As an alternative to tobacco smoking Because friends were using it Out of curiosity	48 (19.2) 27 (10.8) 57 (22.8) 151 (60.4)	15 (15.5) 9 (9.3) 25 (25.8) 64 (66.0)
Relationship with Tobacco when first tried e-cigarettes
ESPAD-TFRI 2019
I have never smoked tobacco I smoked tobacco occasionally I smoke tobacco regularly	461 (66.7) 168 (24.3) 57 (8.9)	149 (58.7) 83 (32.7) 22 (8.7)
SILNE-R-TFRI 2016
I have never smoked tobacco I have tried tobacco but don’t use it regularly I smoked tobacco occasionally/regularly	10 (19.6) 0 (0.0) -	0 (0.0) 0 (0.0)
ESPAD-TFRI 2015
I have never smoked tobacco I smoked tobacco occasionally I smoke tobacco regularly	76 (32.2) 123 (52.1) 37 (15.7)	31 (34.1) 42 (46.1) 18 (19.8)