Int. J. Environ. Res. Public Health 2009, 6 1640 Mexican American children and adolescents had the lowest prevalence rates of exposure and their lower rates were significantly different from the rates for their non-Hispanic white counterparts. Other Hispanic children and adolescents also had significantly lower exposure rates than non-Hispanic Whites. Children, adolescents, and adults born in Mexico had significantly lower exposure than those born in the U.S. Adolescents and adults born in foreign countries other than Mexico also had lower exposure than those who were U.S. born. Education level was inversely related to self-reported SHS exposure for children and adolescents. Children and adolescents living in households headed by someone with less than a high school degree had exposure rates of 32.4% and 26.4% respectively. If the household was headed by someone with education beyond high school, these rates fell to a significantly lower level of 14.7% and 13.6. The exposure rates for adults with education beyond high school were significantly lower than for adults with less than a high school degree (11.9% compared to 17.4%). Poverty status as measured by the PIR was also inversely related to self-reported SHS exposure. Children living in households above the poverty threshold (PIR ≥ 1.0) were significantly less likely to be exposed to SHS in the home than those below the poverty threshold. For children in high income (PIR ≥ 4.0) households, the difference was fivefold (35.3% vs 7.0%). For adolescents, the SHS exposure rates differed significantly by a factor of two for those below the poverty threshold compared to those in high income households (22.6% vs 10.9%). Adults showed the same pattern, though the differences were not statistically significant. 3.3. Cotinine Measured SHS Exposure Table 3 shows the geometric mean of cotinine levels for the three age groups disaggregated by socioeconomic characteristics during the combined years of 1999-2006. Mean cotinine levels were 0.15 ng/mL for children, 0.11 ng/mL for adolescents, and 0.07 mg/mL for adults. Consistent with the self-reported SHS exposure results, adult females had significantly lower cotinine concentration than males. Black adolescents and adults had significantly higher mean cotinine levels than Whites, and Mexican Americans of all ages had significantly lower mean cotinine levels than their white counterparts. Nonsmokers of all ages born in Mexico and anywhere else outside the U.S. had significantly lower mean cotinine levels than those born in the U.S. Both educational level and poverty status were inversely related to the mean self-reported SHS exposure. Adults with education beyond high school, and children and adolescents living in a household with an educated head of household, had significantly lower mean cotinine levels than those with less than a high school education. Compared to those living below the poverty line, all other income groups had significantly lower mean cotinine levels for all three age groups except for low income (PIR = 1.0-1.99) adolescents. The patterns of prevalence rates of detectable serum cotinine among nonsmokers by sociodemographic characteristics during 1999-2006 are similar to the results from Table 2 using self- reported SHS exposure, except that the absolute values of cotinine-measured prevalence rates are much higher. The prevalence rates of cotinine measured exposure were 59.0%, 52.4%, and 40.5% respectively for children, adolescent, and adults. The rates were particularly astonishingly high for non-Hispanic Blacks: 79.6% for children, 75.5% for adolescents, and 62.1% for adults. We do not show detailed results here, but instead only briefly point out some different patterns. Exposure rates