Table 6.

Comparison of literature on exposure to indoor ETS.

Study	Location	Air Quality Assessment	Sample Size	Socio-economic Data	Socio-economic Measure	Results	Significance
Mannino et al. (2001)	US, nationwide	Serum cotinine sample.	5653 children	Study questionnaire	Parental educational attainment; Family poverty index.	Low parental education led to 0.39 ng/ml increase in cotinine levels compared with higher educated parents. Those below the poverty index line had 0.18 ng/ml higher blood cotinine levels.	-Education: p < 0.05* -Poverty index: NSa
Berman et al. (2003)	Los Angeles, US	Parental-reported† home exposure, validated with home nicotine monitor.	242 children	Study questionnaire	Parental educational attainment.	Children with parents who had < high school education had elevated levels of indoor ETS exposure (130.5 h per week) vs. ≥ high school education (109.9 h).	p < 0.05
Jurado et al. (2004)	Granada, Spain	Parental-reported home exposure and urinary cotinine sample.	115 children	Study questionnaire	Parental educational attainment; Household occupant density	The higher the educational level of the father, the lower the cotinine levels in the child. Children living in a house with an occupant density of > 1 per bedroom had higher mean urinary cotinine than those with a household occupant density of < 1 per bedroom.	-Education: p < 0.05 -Occupant density: p = 0.036
Scherer et al. (2004)	Ausburg, Germany	Parental-reported home exposure and urinary cotinine samples.	1220 children	Study questionnaire	Parental educational attainment.	Parental education was a significant predictor of home ETS exposure, with a partial r2 of 3.5. Children of parents with the lowest educational level had approximately 3x higher urinary cotinine levels than children of parents with the highest educational level.	-Reported exposure: p < 0.01 -Cotinine samples:NS
Soliman et al. (2004)	US, nationwide	Parental-reported home exposure.	15,601 families	Study questionnaire	Parental educational attainment.	Children of mothers who were a high school drop out were almost four times more likely (ORb = 1.18) to be exposed to ETS in the home than the children of mothers with a postgraduate education (OR = 0.28).	p < 0.05
Rise et al. (2005)	Norway, nationwide.	Parental-reported home exposure.	212 households	Study questionnaire	Parental educational attainment.	In 1995: parental education was a significant predictor of ETS exposure (β-coefficient = 0.17). 2001: parental education was again a significant predictor of home ETS exposure (β = 0.16).	-1995: p < 0.05 -2001: p < 0.05
Gonzales et al. (2006)	New Mexico, US	Maternal-reported exposure.	269 mothers	Study questionnaire	Maternal educational attainment; Maternal occupational status.	No significant associations were found between educational attainment or occupational status and having a partial or no smoking ban at home.	-Education: p = 0.112 -Occupation: p = 0.572
Bolte et al. (2008)	Bavaria, Germany	Parental-reported home exposure.	12,422 children	Study questionnaire	Parental educational attainment; Parental occupational status. Household income.	Children of parents with a very high education had an adjusted odds ratio (OR) of 1.0 for ETS exposure, compared with very low education of 3.94. Children where both parents were unemployed/marginally employed were almost twice as likely to be exposed to ETS in the home (OR = 1.88) than those who had at least one employed parent (OR = 1.0). Homes with a household income of < 60% of the national median OR = 1.45, compared with homes with the national median household income OR = 1.0.	-Education: p < 0.05 -Occupation: p < 0.05 -Household income: p < 0.05
Hughes et al. (2008)	Seoul, Korea	Parental-reported home exposure.	207 parents	Verbal study questionnaire	Parental educational attainment; Parental occupational status.	35% of parents with < high school education reported home ETS exposure among children, compared with 26% of parents with > college education. 29% of white collar workers vs. 39% of blue collar workers reported childhood ETS exposure in the home.	-Education: p = 0.189 -Occupation: p = 0.581
Akhtar et al. (2009)	Scotland, nationwide	Self-reported home exposure and salivary cotinine sample.	2527 children	Study questionnaire	Family affluence scalec	Children from low affluence families (OR = 3.28) were>3 times more likely to have ‘‘no’’ restrictions over a ‘‘complete’’ smoking ban compared with high affluence families (OR = 1.0). Low FAS score was significantly associated with higher salivary cotinine concentration.	-Restriction: p < 0.05 -Cotinine sample: p < 0.001
Mantziou et al. (2009)	Athens, Greece	Maternal-reported home exposure.	614 children	Study questionnaire	Parental educational attainment.	Lower educated fathers were less likely to expose their children to ETS in the house in comparison to their higher educated peers (OR = 0.57 vs 1.0).	p = 0.077
Akhtar et al. (2010)	Scotland, nationwide	Self-reported home exposure and salivary cotinine sample.	2389 children	Study questionnaire	Family affluence scale; Family SESd	Both low family affluence and SES was associated with a higher proportion of children reporting that one or more parents smoked in the home. Both SES and family affluence were significantly associated with salivary cotinine concentrations.	All regression models: p < 0.001
Alwan et al. (2010)	Leeds, UK	Parental-reported home exposure.	318 homes	Study questionnaire	Parental educational attainment; Parental occupational status.	Low parental education made it 2.2x more likely to smoke in the presence of a child. 53% of unemployed parents smoked in the presence of a child, compared with 37.4% of those employed.	-Education: p < 0.05 -Occupation: p = 0.017
Singh et al. (2010)	US, nationwide.	Parental-reported home exposure.	90,853 children	Verbal study questionnaire	Parental educational attainment; Household poverty statuse	Childhood exposure to ETS in the home was prevalent in 16.44% of households with the lowest paternal education (<12yrs), compared with 1.98% in households with the highest (>16yrs). Smoking occurred in 14.54% of homes with high poverty status, compared with 2.49% in homes with the least poverty.	-Education: p < 0.01 -Poverty status: p < 0.01
Yi et al. (2011)	Korea, nationwide.	Parental-reported home exposure and urinary cotinine samples.	7059 children	Study questionnaire	Parental educational attainment; Household income; Area-level deprivation index	Those with low paternal education had higher odds of ETS exposure (OR = 1.81) than low maternal educational attainment (OR = 1.23), with the equivalent high parental educational group OR of 1.0. Children in homes with a low household income had higher odds of ETS exposure (OR = 1.28), than children in high income homes with (OR = 1.0). The most deprived areas had a higher odds ratio (OR = 1.34), compared with the least deprived areas (OR = 1.0)	-Education: p < 0.05 -Income: p < 0.05 -Area: p < 0.05
Pisinger et al. (2012)	The Capital Region, Denmark	Parental-reported home exposure.	21, 985 parents	Study questionnaire	Parental educational attainment.	OR of home exposure likelihood for children of parents with low education = 11.5, vs OR = 0 for high education: It was 11 times more likely for a child to be exposed to ETS at home if the parent had a very low education.	p < 0.001
Ren et al. (2012)	Detroit, US	Maternal-reported home exposure.	399 children	Study questionnaire	Maternal educational attainment; Household income.	In a sample of mothers who didn’t smoke, 26% of those with a < high school education exposed their children to ETS, compared with 4% of those with > college education. No associations existed between childhood exposure to ETS and maternal household income.	-Education: p < 0.01 -Household income: NS
Hawkins & Berkan (2013)	US, nationwide.	Maternal-reported exposure.	135,278 mothers	Study questionnaire	Maternal educational attainment.	13.4% of mothers with 16 + years of education smoked in the presence of infants for 1 + hours per day, compared with 28.1% of mothers with 0-11yrs education.	p < 0.05
Longman & Passey (2013)	Australia, nationwide	Parental-reported home exposure.	15,978 households.	Census data	Area-level deprivation index	Children living in areas in the lowest deprivation category were 4x more likely to be exposed to ETS in the home (OR = 1), than children in the highest category (OR = 0.25).	p < 0.05
Liao et al. (2014)	Taiwan, statewide	Parental-reported home exposure.	307 parents	Study questionnaire	Parental educational attainment; Parental occupational status; Household income.	55% of parents with > bachelor’s education and 75% of those with < junior high education smoked in the presence of children. 58% of parents with an annual income of >$600,000 smoked in the presence of children, compared with 72% of those where annual income = <$600,000. No associations were significant for occupational status.	-Education: p < 0.05 -Household income = p < 0.05 -Occupation: NS
Raisamo et al. (2014)	Finland, nationwide	Self-reported home exposure.	72,726 adolescents	Study questionnaire	Parental educational attainment.	Paternal educational attainment: in 12-14yo, those with a low paternal education were twice as likely to be exposed to ETS in the home. In 16-18yo, the equivalent group was 1.7x more likely to be exposed to home ETS. Maternal educational attainment: In 12-14yo low educational attainment was 2x as likely to be exposed to ETS in the home (OR = 2.3) than high education attainment (OR = 1.0) 16-18yo, low education OR = 1.7 vs. high OR = 1.0	Paternal education: -12–14: NS -16–18: p = 0.002 Maternal education -12–14: NS -16–18: p = 0.016
Ulbricht et al. (2014)	Mecklenburg, Germany	Parental-reported home exposure.	3570 households	Study questionnaire	Parental educational attainment; Parental occupational status.	Indoor smoking was 5x more likely in households with parents with a low educational attainment (OR = 1), than those with high (OR = 0.19) Unemployed parents were 2.5x more likely to exposure their children to ETS in the home (OR = 2.72) than employed (OR = 1.0)	-Education: p < 0.001 -Occupation: p < 0.001
Shiue (2015)	Scotland, nationwide	Parental-reported home exposure.	1019 children	Study questionnaire	Area-level deprivation index	Loose rules’ regarding indoor smoking were more prevalent in deprived areas vs. non-deprived areas.	p < 0.001
Kuntz & Lampert (2016)	Germany, nationwide	Parental-reported home exposure.	4455 parents	Study questionnaire	Household deprivation index	2006: 46.3% of children of low SES were exposed to ETS in the home, compared with 7.0% of high SES 2012: equivalent measures in 2012 were 19.4 vs. 1.7%	-2006: p < 0.001 -2012; p < 0.001
Yao et al. (2016)	US, nationwide	Self-reported home exposure.	18,731 children; 44,049 adults	Study questionnaire.	Educational attainment; Poverty status.	2000: 35.1% of children with < high school educated parents were exposed to ETS in the home, vs. 9.0% in children who’s parents had a > college degree. 2010: equivalent figures were 9.4% and 8.2%, with no significant difference.	-2000: p < 0.001 -2010: NS
Nguyen et al. (2018)	Japan, nationwide	Self-reported home exposure.	2,891 participants	Study questionnaire.	EA; OS; Household expenditure.	Women with < 9 years of education (OR = 2.37) had a higher risk of passive smoking at the home than women with > 13 years of education (OR = 1.0). Employed woman (OR = 1.44) had a higher chance of home passive smoking than unemployed women (OR = 1.0).	-EA: p < 0.05 -OS: p < 0.05 -Household expenditure: NS

†In studies which assessed childhood exposure to ETS, levels were determined by parental responses.

*values shown in bold were significant at the 95% confidence level.

^aNS – not significant.

^bOR – Odds Ratio

^cFAS – Family Affluence Scale, derived from measures of car & computer ownership, household occupancy & family holidays.

^dSES – Socio-economic status

^eHousehold poverty status - measured as a ratio of family income to federal poverty level.