Order of nicotine e-liquid
1 = 6F-18F-6A-18A
2 = 18F-6F-18A-6A
3 = 6F-18F-18A-6A
4 = 18F-6F-6A-18A

Male/Female
1 = Male
2 = Female

1 = White British
3 = Mixed Race

1 = Employed
2 = Retired
3 = Self-Employed
4 = Studying

Qualification
1 = GCSE
2 = A-Level
3 = Undergraduate
4 = Postgraduate

Method used to stop smoking
1 = e-cigarette
2 = cold turkey

What did you smoke?
1 = ready-rolled
2 = roll your own

How soon did you used to smoke your first cigarette of the day?
1 = within 5 minutes
2 = 6-30 minutes
3 = 31-60 minutes
4 = after 60 minutes

Type of e-cigarette currently used
1 = 2nd generation rechargeable with fluid
2 = modular system (including sub-ohm devices)

How soon after waking do you take your first e-cig puff?
0 = After 60 minutes
1 = 31-60 minutes
2 = 6-30 minutes
3 = within 5 minutes

Do you find it difficult to refrain for e-cig use in places where forbidden?
0 = No
1 = Yes

Which e-cig puffs would you hate most to give up?
0 = Any other ones
1 = First ones in the morning

Do you puff more frequently during the first hours of waking?
0 = no
1 = yes

Do you vape if you are so ill you are in bed most of the day?
0 = no
1 = Yes

For you, stopping vaping completely would be...
1 = Impossible
2 = very difficult
3 = fairly difficult
4 = fairly easy
5 = very easy

Penn State E-cig index - puffs per day
0 = 0-4
1 = 5-9
2 = 10-14
3 = 15-19
4 = 20-29
5 = 30+

Penn State E-cig index how soon after waking (in minutes)
0 = 121+
1 = 61-120
2 = 31-60
3 = 16-30
4 = 6-15
5 = 0-5

Penn State E-cig index -if yes to awaken, how often
0 = 0-1
1 = 2-3
2 = 4+

Penn State E-cig index urge
0 = none/slight
1 = moderate/strong
2 = very strong/extremely

Mood and physical symptom scales depressed
1 = not at all
2 = slightly
3 = somewhat
4 = very
5 = extremely

Baseline Urge to vape in the past week
0 = not at all
1 = a little of the time
2 = some of the time
3 = a lot of the time
4 = almost all of the time
5 = all the time

Baseline Urge to vape - strength of urges
0 = No urges
1 = slight
2 = moderate
3 = strong
4 = very strong
5 = extremely strong

Categorical variable to represent whether user increased or decreased voltage with 6mg nicotine
1 = decrease
2 = stayed the same
3 = increased

Categorical variable to represent whether user increased or decreased voltage with 18mg nicotine
1 = decreased
2 = stayed the same
3 = increased