Int. J. Environ. Res. Public Health 2009, 6 1635 the MEPS indicate that non-Hispanic white and black children were more likely than Hispanic children to live with at least one adult smoker [13]. Previous studies that have examined SHS exposure use several different measures of exposure, including serum cotinine concentration, urinary cotinine concentration, amount of time exposed, whether or not someone in the household smoked in the home, whether or not they lived with a smoker, and whether or not someone in the workplace smoked in their presence. The results are generally consistent, though subtle differences have been found depending on the measure used. The goal of this study is to analyze the pattern of SHS exposure using three measures of SHS exposure: self-reported exposure, whether or not someone has a detectable serum cotinine level, and the actual level of serum cotinine. We will compare the patterns of exposure over time from 1999 to 2006 and by sociodemographic characteristics for different age groups. We will also compare the results from self-reported SHS exposure and cotinine measured exposure estimates. We extend the previous research by focusing on more recent years, and looking at how patterns of exposure differ in an era when all exposure rates are much reduced from previous levels. 2. Methods 2.1. Data Source We analyzed the data from the 1999-2006 National Health and Nutrition Examination Survey (NHANES), which contains a nationally representative sample of noninstitutionalized civilian persons of all ages who were selected based on a complex sampling design. The NHANES is a household survey conducted by the National Center for Health Statistics of the Centers for Disease Control and Prevention to assess the health and nutritional status of adults and children in the U.S. Survey participants complete a home interview followed by a physical examination in a mobile examination center (MEC). The home interviews collect each participant’s demographic and socioeconomic characteristics, dietary patterns, health-related conditions, smoking and tobacco use status, and exposure to SHS. The physical examinations consist of medical, dental, and physiological measurements, as well as laboratory tests including blood and urine samples. During examination in the MEC, blood samples are drawn for serum cotinine analysis for all individuals age 3 and older. Since 1999, the NHANES has been conducted on a continuous basis with data released every two years. Thus, between 1999 and 2006, there were four data release cycles: 1999-2000, 2001-2002, 2003-2004, and 2005-2006. Also, beginning in 1999, non-Hispanic Blacks, Mexican Americans, adolescents 12-19 years, older adults (60+ years), and low-income persons have been oversampled to improve the reliability of the statistical estimates for these subgroups. The response rate of the 1999-2006 NHANES was 81.4% for the home interview and 77.9% for the MEC examination [18]. 2.2. Study Sample While smokers may also suffer ill effects from SHS exposure, it is challenging to separate the health impacts of active and passive smoking. Therefore, in this study we focused only on nonsmokers. Our study sample comprises three age groups of nonsmokers: children (age 3-11), adolescents (age 12-