Table 2. Odds ratios of linear and quadratic models for smoking attitudes among students in England and Scotland (trying smoking is ‘OK’, from 1999-2015) and England only (smoking weekly is ‘OK’, from 2003-2014).

		Trying smoking is OK^a (don’t know = not OK)				Smoking weekly is OK^b (don’t know = not OK)
		Linear	p	Quadratic	p	Linear	p	Quadratic	p
Whole sample (n=165,199; 35,890)	Year	0.91 [0.91 to 0.92]	<0.001	0.87 [0.85 to 0.89]	<0.001	0.91 [0.90 to 0.92]	<0.001	0.72 [0.65 to 0.81]	<0.001
	Year²	-	-	1.00 [1.00 to 1.00]	<0.001	-	-	1.01 [1.01 to 1.02]	<0.001
	Level	1.03 [0.97 to 1.10]	0.330	1.05 [0.98 to 1.12]	0.143	1.15 [1.00 to 1.32]	0.045	1.10 [0.96 to 1.27]	0.152
	Post-slope	0.92 [0.90 to 0.93]	<0.001	0.88 [0.86 to 0.90]	<0.001	0.95 [0.90 to 1.00]	0.032	0.82 [0.75 to 0.89]	<0.001
Male only subgroup (n=82,270; 18,042)	Year	0.92 [0.91 to 0.93]	<0.001	0.84 [0.81 to 0.87]	<0.001	0.92 [0.91 to 0.94]	<0.001	0.67 [0.57 to 0.79]	<0.001
	Year²	-	-	1.01 [1.00 to 1.01]	<0.001	-	-	1.02 [1.01 to 1.03]	<0.001
	Level	1.08 [0.99 to 1.18]	0.090	1.11 [1.01 to 1.22]	0.024	1.33 [1.10 to 1.62]	0.004	1.27 [1.04 to 1.54]	0.020
	Post-slope	0.91 [0.89 to 0.93]	<0.001	0.84 [0.81 to 0.88]	<0.001	0.88 [0.82 to 0.94]	<0.001	0.71 [0.62 to 0.81]	<0.001
Female only subgroup (n=82,929; 17,848)	Year	0.90 [0.90 to 0.91]	<0.001	0.89 [0.86 to 0.93]	<0.001	0.90 [0.88 to 0.91]	<0.001	0.77 [0.66 to 0.91]	0.001
	Year²	-	-	1.00 [1.00 to 1.00]	0.492	-	-	1.01 [1.00 to 1.02]	0.067
	Level	0.98 [0.90 to 1.07]	0.718	0.99 [0.90 to 1.08]	0.789	1.02 [0.84 to 1.22]	0.866	0.99 [0.82 to 1.19]	0.917
	Post-slope	0.93 [0.91 to 0.95]	<0.001	0.92 [0.88 to 0.95]	<0.001	1.01 [0.95 to 1.08]	0.720	0.92 [0.81 to 1.04]	0.180
13 year olds only (n=85,713; 18,721)	Year	0.90 [0.89 to 0.91]	<0.001	0.89 [0.86 to 0.92]	<0.001	0.90 [0.89 to 0.92]	<0.001	0.78 [0.65 to 0.94]	0.007
	Year²	-	-	1.00 [1.00 to 1.00]	0.459	-	-	1.01 [1.00 to 1.02]	0.107
	Level	0.95 [0.86 to 1.05]	0.321	0.95 [0.87 to 1.05]	0.349	1.22 [0.97 to 1.53]	0.086	1.19 [0.94 to 1.49]	0.145
	Post-slope	0.94 [0.92 to 0.97]	<0.001	0.93 [0.90 to 0.97]	<0.001	0.93 [0.85 to 1.01]	0.092	0.84 [0.73 to 0.98]	0.022
15 year olds only (n=79,486; 17,169)	Year	0.93 [0.92 to 0.94]	<0.001	0.86 [0.83 to 0.89]	<0.001	0.91 [0.90 to 0.93]	<0.001	0.70 [0.60 to 0.80]	<0.001
	Year²	-	-	1.00 [1.00 to 1.01]	<0.001	-	-	1.01 [1.01 to 1.02]	<0.001
	Level	1.09 [1.01 to 1.19]	0.034	1.13 [1.04 to 1.23]	0.006	1.11 [0.94 to 1.32]	0.218	1.06 [0.90 to 1.26]	0.473
	Post-slope	0.89 [0.87 to 0.91]	<0.001	0.83 [0.80 to 0.86]	<0.001	0.96 [0.90 to 1.02]	0.144	0.80 [0.71 to 0.89]	<0.001

available for England and Scotland only

available for England only