Int. J. Environ. Res. Public Health 2009, 6 Education Level 2 < High School (reference) High School or GED > High School Unknown 0 - 0.99 (reference) 1 - 1.99 2 - 3.99 ≥ 4.0 Unknown 1607 1178 2285 97 1725 1361 1126 637 318 0.28 0.24 0.10 0.25 -0.202* -0.788* 0.034 Table 3. Cont. 2014 0.17 1341 0.17 2696 0.08 171 0.15 Poverty Income Ratio -0.091 -0.632* -0.145 3704 2766 6126 16 0.09 0.08 0.06 -- 0.34 -0.529* 1795 0.18 -0.118 1814 0.10 0.21 -1.143* 1512 0.15 -0.458* 2982 0.08 0.10 -1.692* 1532 0.10 -0.820* 3368 0.07 0.06 -0.684* 955 0.07 -0.327* 3529 0.06 0.17 428 0.12 919 0.08 1 Data source: National Health and Nutrition Examination Survey. 2 Unweighted 2 For children and adolescents, these numbers reflect their household reference person's status. -- Results are not shown for sample size of 20 or smaller. * Regression coefficient is statistically significant at P-value < 0.05. Note: All the cotinine means and regression coefficients are based on weighted analyses accounting for complex survey design. 1643 -0.038 -0.279* -- -0.226* -0.380* -0.503* -0.219* 3.4. Comparison of Self-Reported and Cotinine Measured SHS Exposure Our results indicate much higher rates of cotinine measured exposure than self-reported SHS exposure. To further analyze how these exposure measures differ, we calculated the prevalence rates of detectable cotinine and the geometric means of cotinine concentration separately for nonsmokers who self-reported SHS exposure and those who did not (Table 4). 98.2% of children with self-reported exposure had detectable serum cotinine levels, with a geometric mean of 1.20 ng/mL. For children who did not have self-reported exposure, almost half (47.6%) of them nonetheless had detectable serum cotinine, with a mean value of 0.08 ng/mL. The pattern is similar for adolescents, though only 42% of those who report no home exposure had detectable cotinine, and the mean cotinine level for those with self-reported home exposure was lower than that of children: 0.75 ng/mL. For adults, the agreement between self-reported and cotinine-indicated exposure is greater for those who reported being exposed only in the home (94.2%) or both in the home and work (98.4%). For those who report being exposed only at work, 63.5% have detectable cotinine. More than one-third of adults (36.1%) who report that they were not exposed in the home or at work nonetheless had detectable cotinine levels. Geometric means of cotinine concentration were greatest for adults who report being exposed both in the home and at work (0.65 ng/mL), followed by those who report only home exposure (0.52 ng/mL). Levels were lowest for those who report being exposed only at work (0.11 ng/mL). Multivariate logistic regression models were used to examine the relationship between self-reported SHS exposure and cotinine measured exposure. We regressed the presence of detectable cotinine (yes/no) on self-reported exposure (yes/no) adjusting for sociodemographic characteristics. For children and adolescents, only self-reported home exposure was included in the model. For adults, three self-reported variables, exposure at home only, at work only, and both at home and at work, were included in the model. The results show that self-reported SHS exposure is a statistically significant