Table 3

Results of nested logistic models in the prediction of smoking status at 50 years (N=8218)

	Model 0: sex, social class at 50 OR (95% CI)	Model 1: model 0+adult conscientiousness OR (95% CI)	Model 2: model 1+educational qualifications OR (95% CI)	Model 3: model 2+cognitive ability at 7 OR (95% CI)	Model 4: model 3+attention problems at 7 OR (95% CI)	Model 5: model 4+conduct problems at 7 OR (95% CI)	Model 6: model 5+social class at birth OR (95% CI)	Model 7: model 6+childhood conscientiousness OR (95% CI)
Sex
Male	1	1	1	1	1	1	1	1
Female	1.09 (0.97, 1.23)	1.11 (0.99, 1.25)#	1.10 (0.97, 1.24)	1.10 (0.97, 1.24)	1.10 (0.98, 1.25)	1.15 (1.01, 1.30)*	1.13 (1.00, 1.28)*	1.20 (1.06, 1.36)**
Social class at 50
I	1	1	1	1	1	1	1	1
II	1.73 (1.27, 2.35)***	1.71 (1.26, 2.33)***	1.51 (1.11, 2.07)**	1.51 (1.10, 2.06)*	1.50 (1.10, 2.06)*	1.50 (1.10, 2.06)*	1.48 (1.08, 2.03)*	1.37 (0.99, 1.88)#
IIIN	2.10 (1.52, 2.90)***	2.08 (1.51, 2.87)***	1.56 (1.11, 2.18)*	1.55 (1.11, 2.17)*	1.54 (1.10, 2.16)*	1.54 (1.10, 2.16)*	1.52 (1.09, 2.14)*	1.46 (1.03, 2.06)*
IIIM	3.45 (2.52, 4.72)***	3.37 (2.46, 4.61)***	2.34 (1.69, 3.26)***	2.32 (1.67, 3.23)***	2.31 (1.66, 3.22)***	2.27 (1.63, 3.17)***	2.18 (1.57, 3.05)***	1.93 (1.37, 2.70)***
IV	3.85 (2.78, 5.34)***	3.74 (2.70, 5.19)***	2.50 (1.78, 3.53)***	2.48 (1.76, 3.51)***	2.48 (1.75, 3.50)***	2.45 (1.73, 3.46)***	2.36 (1.67, 3.34)***	2.15 (1.51, 3.07)***
V	4.79 (3.21, 7.14)***	4.62 (3.10, 6.89)***	2.82 (1.89, 4.29)***	2.79 (1.84, 4.25)***	2.78 (1.83, 4.24)***	2.75 (1.81, 4.19)***	2.61 (1.71, 3.97)***	2.37 (1.55, 3.62)***
X2 (DF)	200.11 (6)***
Conscientiousness at 50		0.98 (0.97, 0.995)**	0.99 (0.98, 0.998)*	0.99 (0.98, 0.998)*	0.99 (0.98, 0.998)*	0.99 (0.98, 0.999)*	0.99 (0.98, 1.00)*	1.00 (0.98, 1.01)
X2 (DF)		211.01 (7)***
		Model improvement: p<0.001
Qualifications at 50
1			1	1	1	1	1	1
2			0.72 (0.57, 0.89)**	0.72 (0.57, 0.90)**	0.72 (0.58, 0.90)**	0.73 (0.58, 0.92)**	0.74 (0.59, 0.93)**	0.80 (0.63, 1.00)*
3			0.55 (0.45, 0.66)***	0.55 (0.45, 0.67)***	0.55 (0.45, 0.67)***	0.58 (0.48, 0.70)***	0.59 (0.49, 0.72)***	0.70 (0.57, 0.85)**
4			0.47 (0.38, 0.59)***	0.48 (0.38, 0.59)***	0.48 (0.39, 0.60)***	0.50 (0.41, 0.63)***	0.52 (0.42, 0.64)***	0.60 (0.42, 0.85)**
5			0.38 (0.31, 0.46)***	0.38 (0.31, 0.47)***	0.39 (0.31, 0.47)***	0.41 (0.33, 0.50)***	0.43 (0.35, 0.53)***	0.59 (0.47, 0.74)***
6			0.31 (0.20, 0.48)***	0.32 (0.21, 0.49)***	0.32 (0.21, 0.49)***	0.35 (0.22, 0.53)***	0.37 (0.24, 0.56)***	0.80 (0.29, 0.83)**
X2 (DF)			317.39 (12)***
			Model improvement: p<0.001
Cognitive ability at 7
Lowest				1	1	1	1	1
2nd				1.07 (0.90, 1.28)	1.07 (0.90, 1.28)	1.08 (0.91, 1.29)	1.08 (0.91, 1.29)	1.07 (0.90, 1.28)
3rd				0.97 (0.79, 1.18)	0.97 (0.80, 1.19)	0.99 (0.81, 1.21)	1.00 (0.81, 1.23)	0.98 (0.80, 1.20)
4th				1.04 (0.83, 1.22)	1.01 (0.83, 1.23)	1.04 (0.85, 1.27)	1.05 (0.86, 1.29)	1.04 (0.86, 1.27)
Highest				0.94 (0.77, 1.13)	0.95 (0.78, 1.14)	0.98 (0.81, 1.27)	1.00 (0.82, 1.21)	1.00 (0.83, 1.21)
X2 (DF)				320.33 (16)***
				Model improvement: p=0.58
Attention problems at 7
Never					1	1	1	1
Sometimes					1.10 (0.95, 1.27)	1.08 (0.93, 1.24)	1.07 (0.93, 1.24)	1.03 (0.89, 1.19)
Frequently					1.15 (0.92, 1.43)	1.10 (0.88, 1.37)	1.08 (0.87, 1.35)	1.04 (0.83, 1.31)
X2 (DF)					323.51 (18)***
					Model improvement: p=0.23
Conduct problems at 7						1.05 (1.03, 1.08)***	1.05 (1.02, 1.08)***	1.03 (1.00, 1.06)*
X2 (DF)						339.30 (19)***
						Model improvement: p<0.001
Social class at birth
I							1	1
II							1.00 (0.71, 1.42)	1.11 (0.65, 1.88)
IIIN							1.10 (0.77, 1.58)	1.08 (0.52, 2.22)
IIIM							1.20 (0.88, 1.65)	1.26 (0.76, 2.08)
IV							1.20 (0.84, 1.70)	1.22 (0.72, 2.06)
V/no job/single parent							1.74 (1.24, 2.44)**	1.75 (1.03, 2.97)*
X2 (DF)							370.58 (24)***
							Model improvement: p<0.001
Childhood conscientiousness								0.86 (0.84, 0.88)***
X2 (DF)								568.38 (25)***
								Model improvement: p<0.001
Explained proportion of social gradient in relation to model 0 (reduction)		3.6%	41.1%	41.8%	42.0%	42.6%	45.5%	50.5%

Nested logistic regression models were compared to investigate the influence of conscientiousness on the social gradient of smoking at age 50. The uncorrected social gradient for smoking based on social class at age 50 was tested in model 0 (controlled for sex). Models 1–7 then successively introduced adult conscientiousness, educational qualifications at 50, cognitive ability at age 7, attention problems at age 7, conduct problems at age 7, social class at birth and childhood conscientiousness at 16. The row immediately beneath each variable gives the χ² and degrees of freedom (DF). A significant change in χ² allowing for the change in DF shows whether each additional variable significantly improved the previous model. The explained proportion of social gradient in row 4 was calculated by relating the absolute difference between the OR of age 50 social class V of models 1–7 and the baseline OR of age 50 social class V in model 0 to the baseline OR (in (%)). *p<0.05; **p<0.01; ***p<0.001; #p<0.10.