Table 1. Wave 1 predictor variables used with details of which stage they were eliminated from consideration.

For each of the 65 Wave 1 predictor variables considered, Table 1 gives details of their type (graded or continuous) and of the stage at which they were eliminated from consideration for the final propensity score.

Group		Variables	Levels or continuous a	Eliminated at stage 1 b	Eliminated at stage 2 c	Eliminated at stage 3 d
1		Demographic variables
	1	Age range	2	No → A	No → F	No → P
	2	Gender	2	No → A	No → F	No → P
	3	Hispanic origin	2	Yes
	4	Race	3	Yes
	5	Census region	4	Yes
2		Education, internalizing disorders
	6	Highest grade or year at school completed by parent	5	Yes
		Last time significant problems with:
	7	(a)   Feeling very trapped, lonely, sad, blue, depression	4	No → A	No → F	Yes
	8	(b)   Sleep trouble – such as bad dreams, sleeping restlessly	4	Yes
	9	(c)   Becoming very distressed when something reminded of past	4	No → A	Yes
3		Susceptibility to smoking
	10	Ever been curious about smoking a cigarette	4	No → B	No → F	No → P
	11	Think you will smoke a cigarette in the next year	4	No → B	No → F	No → P
	12	Think you will try a cigarette soon	4	Yes
	13	Would smoke a cigarette if one your best friends offered you one	4	Yes
4		Externalizing disorders
		Last time 2+ times
	14	(a)   Lied or conned to get things you wanted or avoid doing something	4	No → B	Yes
	15	(b)   Had a hard time paying attention at school, work or home	4	No → B	Yes
	16	(c)   Had a hard time listening to instructions at school, work or home	4	Yes
	17	(d)   Were a bully or threatened other people	4	Yes
	18	(e)   Started physical fights with other people	4	No → B	Yes
	19	(f)   Felt restless or the need to run around or climb things	4	Yes
	20	(g)   Gave answers before the other person finished asking the question	4	Yes
5		Attitudes to tobacco
		Agree/disagree
	21	(a)   I think I would enjoy using tobacco	4	No → B	No → F	No → P
	22	(b)   Using tobacco would be energizing	4	Yes
	23	(c)   Using tobacco would help me reduce or handle stress	4	No → B	Yes
	24	(d)   Using tobacco would help me calm down when I am angry	4	Yes
	25	(e)   Using tobacco would help me control my weight	4	Yes
	26	(f)   Using tobacco would help me feel more comfortable at parties	4	Yes
	27	How much you think people harm themselves when they smoke cigarettes every day	4	Yes
	28	How much you think people harm themselves when they smoke cigarettes some but not every day	4	Yes
	29	How long do you think someone has to smoke cigarettes before it harms their health	6	Yes
	30	Agree/disagree: some tobacco products are safer than others	5	No → B	No → F	No → P
	31	Seen a tobacco sweepstakes ad in past 6 months	2	Yes
6		Substance use
	32	Ever used alcohol at all	2	No → B	No → F	No → P
	33	Ever used prescription drug not prescribed to you: Ritalin or Adderall	2	No → B	No → F	No → P
	34	Ever used prescription drug not prescribed to you: Painkillers, sedatives or tranquilizers	2	Yes
	35	Ever used substance: Cocaine or crack	2	Yes
	36	Ever used substance: Stimulants like methamphetamine or speed	2	Yes
	37	Ever used substance: Any other drugs like heroin, inhalants, solvents or hallucinogens	2	Yes
7		Risk taking variables
		Agree/disagree:
	38	(a)   Like to do frightening things	5	Yes
	39	(b)   Like new and exciting experiences even if I have to break the rules	5	No → C	No → F	Yes
	40	(c)   Prefer friends who are exciting and unpredictable	5	No → C	No → F	No → P
8		School performance, Health Behaviour Overall, Anxiety
	41	Youth’s grade performance in school in past 12 months	10	No → C	No → F	Yes
	42	How often youth missed school due to illness in past 12 months	5	Yes
	43	Youth’s overall health status (as reported by parent or guardian)	5	Yes
	44	Last time problems with: feeling very anxious, nervous, tense, scared, panicked	4	No → C	Yes
9		Accessibility to tobacco, Susceptibility to social influences
	45	How easy you think it is for people your age to buy tobacco products in a store	4	No → C	Yes
	46	Hours spent watching TV on a typical day	5	Yes
	47	How often do you use the internet	7	Yes
	48	Has a Facebook, Google Plus, MySpace, Twitter or other social networking	2	No → C	No → F	No → P
10		Family-related variables
	49	Parent has a spouse or partner that lives in household	2	Yes
	50	Cigarettes or tobacco might be available to youth at parent or guardian’s home	2	Yes
	51	Anyone who lives with you now uses tobacco	3	No → C	No → F	No → P
	52	Number of hours in past 7 days you were in close contact with others when they were smoking	C	Yes
	53	Parent or guardian marital status	3	Yes
	54	Youth has a curfew or set time to be home on school nights	2	Yes
	55	Youth has a curfew or set time to be home on weekend nights	2	Yes
	56	Rules about using tobacco products that are burned inside home	3	Yes
	57	Statement that best describes the rules about using combustible tobacco	3	No → C	Yes
	58	Parent or guardian talk with you, even once about not using any type of tobacco	2	Yes
	59	Reaction of parent/guardian found you using tobacco	3	No → C	No → F	No → P
11		Pocket money allowance, Movie influence
	60	Money received in total during an average week	9	No → A	No → F	Yes
	61	Number of times seen Movie 1	4	Yes
	62	Number of times seen Movie 2	4	No → A	No → F	Yes
	63	Number of times seen Movie 3	4	No → A	Yes
	64	Number of times seen Movie 4	4	No → A	No → F	Yes
	65	Number of times seen Movie 5	4	Yes

^aFor graded variables, the number of levels is shown in the table, and the levels they represent is shown below. Continuous variables are indicated by the letter C. Exceptionally variables 10–13 were treated as a continuous variable with levels 1 to 4.

^b Those not eliminated at stage 1 went into stage 2 analyses A, B or C as indicated.

^cThose variables not eliminated at stage 2 went into stage 3 (final = F) analysis.

^dThose variables not eliminated at stage 3 were included in the propensity score (P).