Misclassification of smoking habits: An updated review of the literature

Table 1 Distribution of study characteristics among the 294 detailed results

Factor	Level	No. of results analyseda
Body fluid	Urine	78a
	Saliva	90
	Blood	126
Assay method	Chromatography	93
	Spectrometry	72
	Immunoassay	108
	Other	21a
Age groupb	Young	103
	Not young	35
	All ages	108a
	Not stated	48
Study type	General population	189a
	Pregnancy	57
	Diseased or case-control	48
Awareness of validation by cotinine	Yes	22a
	No	47
	Not specified	225
Time of publication	Studies considered in the 1995 review	31
	Studies reported before 2003	109
	Studies reported later	154a
Study quality	Good	36
	Not good	258a
Pregnancy (women only)	Not pregnant	61
	Pregnant	57
Tobacco products considered	Cigarettes	108
	Any smoking	160
	Any tobacco	26a
Sex	Females	118
	Males	48
	Combined	128a
Location	Canada/United States	115a
	Europe	128
	Asia	25
	Other	26

^aFactor levels with this superscript are the levels applicable to the very large study by Palmier J, Lanzrath B, Dixon A and Idowu O[26] considered separately in our analyses.

^bStudies varied in how they reported the age range studied, sometimes giving a specific range of ages, sometimes a mean age and sometimes no information.

The categories were based on the available age information as follows: Young: Upper age limit < 50 or mean age < 30 or a pregnancy study; Not young: Lower age limit 30+ or mean age 60+, thus excluding young people; All ages: Lower age limit < 30 and upper age limit 50+ or lower age limit < 30 and mean age 30+; Not stated: All other combinations.

Table 2 Misclassification rates from Palmier et al[26] and from the other studies combined by meta-analysis (based on weighted analysis, avoiding double-counting)

Rate		Other studies combined				Palmier
		Cut 1a		Cut 2b		Cut 2b
		n	Rate (95%CI)	n	Rate (95%CI)	Rate
M1	% of self-reported non-smokers whose cotinine implies current smoking	209	4.96 (4.32 to 5.60)	65	3.66 (2.68 to 4.65)	2.01
M2	% of self-reported never smokers whose cotinine implies current smoking	86	3.00 (2.45 to 3.54)	22	2.34 (1.28 to 3.41)	-
M3	% of self-reported ex-smokers whose cotinine implies current smoking	88	10.92 (9.23 to 12.61)	24	6.79 (4.60 to 8.98)	-
M4	% of self-reported current smokers whose cotinine implies non-smoking	142	9.67 (7.73 to 11.61)	44	18.48 (14.46 to 22.50)	53.08
M5	% of true current smokers who report being non-smokers	136	14.50 (12.36 to 16.65)	43	10.42 (5.91 to 14.92)	19.31
M6	% of true current smokers who report being never smokers	52	5.70 (3.20 to 8.20)	13	4.34 (0.19 to 8.49)	-
M7	% of true current smokers who report being ex-smokers	52	8.93 (6.57 to 11.29)	13	7.89 (4.07 to 11.71)	-
M8	% of self-reported current smokers (plus misclassified non-smokers) who report being non-smokers	185	11.59 (10.00 to 13.17)	60	7.92 (5.19 to 10.65)	10.10
M9	% of self-reported current smokers (plus misclassified non-smokers) who report being never smokers	66	4.64 (2.73 to 6.54)	21	4.02 (1.68 to 6.35)	-
M10	% of self-reported current smokers (plus misclassified non-smokers) who report being ex-smokers	66	7.72 (5.95 to 9.50)	21	5.69 (3.54 to 7.84)	-
M11	% of true non-smokers who report being current smokers	137	3.65 (2.84 to 4.45)	43	7.67 (6.14 to 9.20)	8.84

^aThe lower cut point.

^bThe higher, more conservative, cut point.

Table 3 Distribution of misclassification rate values from the studies included in Table 2 for the lower cut point (Cut 1)

		< 2%	2% to < 5%	5% to < 10%	10% to < 25%	25% to < 50%	> 50%	Total
M1	% of self-reported non-smokers whose cotinine implies current smoking	45	741	51	31	3	5	209
M2	% of self-reported never smokers whose cotinine implies current smoking	441	25	13	4	0	0	86
M3	% of self-reported ex-smokers whose cotinine implies current smoking	2	7	31	381	7	3	88
M4	% of self-reported current smokers whose cotinine implies non-smoking	16	29	341	42	18	3	142
M5	% of true current smokers who report being non-smokers	5	18	28	521	22	11	136
M6	% of true current smokers who report being never smokers	18	131	10	7	2	2	52
M7	% of true current smokers who report being ex-smokers	4	16	171	7	7	1	52
M8	% of self-reported current smokers (plus misclassified non-smokers) who report being non-smokers	11	30	42	651	28	9	185
M9	% of self-reported current smokers (plus misclassified non-smokers) who report being never smokers	25	191	11	7	2	2	66
M10	% of self-reported current smokers (plus misclassified non-smokers) who report being ex-smokers	7	21	221	10	5	1	66
M11	% of true non-smokers who report being current smokers	45	511	27	12	2	0	137

¹Includes the median.

Table 4 For each factor, the significance of the differences in rates between the factor levels: Cut 1, univariate analyses

Rate		Body fluid	Assay method	Study type	Age group	Aware validated	Time published	Study quality	Pregnancy	Tobacco products	Sex	Location	Sex × location
M1	% of self-reported non-smokers whose cotinine implies current smoking	NS	NS	c1	NS	NS	NS	NS	NS	NS	NS	NS	NS
M2	% of self-reported never smokers whose cotinine implies current smoking	NS	NS	NS	b	NS	NS	a	NS	d1	NS	b	d
M3	% of self-reported ex-smokers whose cotinine implies current smoking	a	b	d1	d	c	a	NS	d	a1	a	c	b
M4	% of self-reported current smokers whose cotinine implies non-smoking	NS	b	d1	d1	NS	d1	NS1	NS	NS	NS	NS	NS
M5	% of true current smokers who report being non-smokers	NS	NS	b	NS	NS	d1	NS	NS	NS	NS	NS	c1
M6	% of true current smokers who report being never smokers	NS	NS	NS	NS	NS	NS	NS	NS	NS	b	NS	d1
M7	% of true current smokers who report being ex-smokers	NS	NS	d1	c	NS	b	NS	a	NS	NS	NS	NS
M8	% of self-reported current smokers (plus misclassified non-smokers) who report being non-smokers	NS	NS	NS	a	b	d1	a	NS	b	NS	NS	d1
M9	% of self-reported current smokers (plus misclassified non-smokers) who report being never smokers	a	NS	NS	NS	NS	NS1	NS	NS	NS	b	NS	d1
M10	% of self-reported current smokers (plus misclassified non-smokers) who report being ex-smokers	NS	NS	d1	c	NS	b	NS	b	NS	b	NS	NS
M11	% of true non-smokers who report being current smokers	b	NS	d1	d1	NS	NS	NS	NS	NS	NS	a	NS

^dP < 0.001.

^cP < 0.01.

^bP < 0.05.

^aP < 0.1.

NS (not significant): P ≥ 0.1.

¹For each rate (M1-M11) identify the variables that, in multivariate analysis, were independently statistically significantly (P < 0.01) associated with the misclassification rate. NS: Not significant.

Table 5 Factors included in the final model for a rate, with the significant differences in misclassification rates (from base level) by factor level: Cut 1, multivariate analysis

Factor (base level), rates that included the factor in multivariate analysisa		Other factor levels: Difference in rate from base level, significancea
Study type (base level = general population)		Pregnancy	Diseased/case-control
M1	% of self-reported non-smokers whose cotinine implies current smoking		3.92++
M3	% of self-reported ex-smokers whose cotinine implies current smoking	14.63+++	3.89+
M4	% of self-reported current smokers whose cotinine implies non-smoking	-14.24---	10.71++
M7	% of true current smokers who report being ex-smokers		14.74+++
M10	% of self-reported current smokers (plus misclassified non-smokers) who report being ex-smokers		9.11+++
M11	% of true non-smokers who report being current smokers	-2.48-	6.92+++
Age group (base level = young)		Not young	All ages	Not stated
M4	% of self-reported current smokers whose cotinine implies non-smoking	-11.03-	-16.86---	-18.28---
M11	% of true non-smokers who report being current smokers		-3.87---	-4.58--
Time of publication (base level = in 1995 review)		Before 2003	2003 onwards
M4	% of self-reported current smokers whose cotinine implies non-smoking		11.17++
M5	% of true current smokers who report being non-smokers		9.61(+)
M8	% of self-reported current smokers (plus misclassified non-smokers) who report being non-smokers		6.26+
M9	% of self-reported current smokers (plus misclassified non-smokers) who report being never smokers		6.11++
Study quality (base level = good)		Not good
M4	% of self-reported current smokers whose cotinine implies non-smoking	6.32++
Tobacco products considered (baseline level = cigarettes)		Any smoking	Any tobacco
M2	% of self-reported never smokers whose cotinine implies current smoking	-2.22---
M3	% of self-reported ex-smokers whose cotinine implies current smoking	-3.61-
Location in females (base level = Canada/United States)c		Europe	Asia	Other
M5	% of true current smokers who report being non-smokers	6.73(+)	23.61+++
M6	% of true current smokers who report being never smokers	-11.06(-)	27.32++
M8	% of self-reported current smokers (plus misclassified non-smokers) who report being non-smokers		23.19+++
M9	% of self-reported current smokers (plus misclassified non-smokers) who report being never smokers	-8.62-	30.96+++	24.27+b

^aFor each factor, the rates shown are those with which the factor showed a significant (P < 0.01) independent association. All differences shown are adjusted for the other factors significant for that rate. They represent the difference in misclassification rate from the rate for the base level. Only statistically significant differences are shown. The significance of the difference is coded as: ⁺⁺⁺P < 0.001; ^---P < 0.001; ⁺⁺P < 0.01; ^--P < 0.01; ⁺P < 0.05; ^-P < 0.05; ⁽⁺⁾P < 0.1; ^(-)P < 0.1.

^bResult based on three estimates or less.

^cVariations between location were generally not significant for males or for sexes combined - see Supplementary File 3 for full results for sex × location.