Table 1

Parameters for the best fitting segmented regression models of smoking prevalence, ever-smoking prevalence in young adults and quit ratios in Great Britain between 1973 and 2016

	Smoking prevalence				Ever-smoking prevalence in young adults				Quit ratios
	Β	95% CI		P value	Β	95% CI		P value	Β	95% CI		P value
Intercept	47.548	45.951	49.144	<0.001	57.667	56.466	58.867	<0.001	25.573	22.698	28.448	<0.001
Time	−1.456	−1.719	−1.193	<0.001	−1.608	−1.840	−1.376	<0.001	1.868	1.399	2.336	<0.001
Time² 0 to BP1	0.026	0.017	0.035	<0.001	0.050	0.041	0.059	<0.001	−0.039	−0.055	−0.023	<0.001
Time² BP1 to BP2	−0.191	−0.345	−0.037	0.017	−0.168	−0.196	−0.139	<0.001	0.059	0.023	0.095	0.002
Time² BP2 to BP3	0.167	0.009	0.342	0.062	0.140	0.103	0.177	<0.001	0.527	0.080	0.975	0.023

Smoking prevalence, quadratic model with two breakpoints in 2000 (year 27) and 2001 (year 28); ever-smoking prevalence in young adults, quadratic model with two breakpoints in 1994 (year 21) and 2002 (year 29); quit ratio, quadratic model with two breakpoints in 1996 (year 23) and 2013 (year 40).