Kim and Ruger BMC Public Health 2010, 10:195 http://www.biomedcentral.com/1471-2458/10/195 latter were 2.7 times more likely to develop CHD than the former [14]. Although concerns over health inequality have grown recently, studies on socioeconomic inequalities in health in Asia, and particularly in the Republic of Korea, are lim- ited [5,6,15]. Furthermore, previous studies of education, occupation and income on health behaviors have pro- duced mixed results [6,15-24]. One study found that edu- cation level was related to mortality [6], another found that mortality across education levels remained unchanged over a ten-year period [17], while another found no educational differences in mortality from coro- nary artery disease for women aged 55 to 64, while mor- tality in those aged 35 to 54 is inversely related to education level [22], as found in Western Europe and the U.S. Furthermore, previous work varies in the consider- ation of behavioral risk factors, which could play a signifi- cant role in health inequalities [15]. Studies exploring the role of behavioral risk on the relationship between body mass index (BMI) and mortality, for example, provide inconsistent results [25-29]. Some researchers find a strong J-shape or U-shape correlation between BMI and mortality [26-28], whereas a recent study showed that the role of BMI was statistically insignificant, after adjusting for income level [29]. A common limitation is that previ- ous studies have typically focused on either subjective health measures or self-reported acute and chronic dis- ease; few have studied both simultaneously, and fewer still have done so taking gender and behavioral risk fac- tors into account [3,30] and employing data from nation- ally representative surveys. Conflicting findings from previous studies [6,21,22], combined with limited scope and study populations, demonstrate the need to examine simultaneously, in a national probability sample, various social and economic measures [31-34], behavioral risk factors [35,36], and acute and chronic disease and subjec- tive health measures [34,37] among both men and women in studying health inequality [14,16,24,38-40]. Few studies have focused on how gender differences affect the impact of socioeconomic position on health [22-24]. To our knowledge, this is the first study in South Korea to examine socioeconomic inequalities by three different indicators (education, occupation, and income) in both self-reported acute and chronic disease and subjective health conditions among men and women respectively, controlling for behavioral risk factors (smoking, drinking, obesity, exercise, and sleep), marital status and age. This study tests whether socioeconomic health inequalities differ by: (i) gender; (ii) self-reported or self-rated (sub- jective) health measures; or (iii) socioeconomic indica- tors (income, occupation, or education) and whether these associations between socioeconomic positions and health inequality persist over time. Page 2 of 19 Methods Data Data for this study are from the Korea National Health and Nutrition Examination Survey (KNHANES), con- ducted in 1998 and in 2005. The KNHANES is a nation- ally representative survey sponsored by the Korean Ministry of Health and Welfare and consists of four parts: the Health Interview Survey (HIS), the Health Examina- tion Survey (HES), the Health Behavior Survey (HBS) and the Nutrition Survey (NS). The HIS and HBS contain data estimating the national prevalence of selected dis- eases and risk factors. The survey procedure consisted of personal household interviews comprising questions on morbidity, activity levels, medical care and health behav- ior. The HES estimates national population reference dis- tributions of selected health parameters, including pulse rate, blood pressure, cholesterol, triglycerides, fasting blood sugar, hemoglobin, blood urea nitrogen (BUN), creatinine, serum glutamic oxaloacetic transaminase (SGOT), serum glutamine pyruvic transaminase (SGPT), and hepatitis B antigen and antibody. The NS collects information on dietary practices. Overall, the KNHANES collects detailed information on health status, health care use and expenses, and health insurance coverage. For this study's purposes, the respondents included men and women aged 30 and over who participated in the HBS. Adults under 30, who perhaps had not yet completed their education and acquired income or employment, were excluded. The KNHANES uses a stratified multistage probability sampling design. Because each sample in the survey was not equally selected and involved stratification and clus- tering, our study required a sampling weight for unbiased national estimates; all estimates in the text and tables have been weighted accordingly. For the 1998 survey, a total number of 12283 Korean households with 39060 household members of all ages took part in the main interview, out of a total sample of 43682 eligible persons, yielding a response rate of 89.4% (HBS: 9808 persons from 13218 persons aged 10 and over with a response rate of 74.2%; HES: 9771 persons from 13420 persons aged 10 and over with a response rate of 72.8%; NS: 11525 persons from 15475 persons with a response rate of 74.5%). For the 2005 survey, 25207 persons out of 25453 completed the main HIS interview with a person-level response rate of 99.1% (HBS: 8835 persons from 9516 persons with a response rate of 92.8%; HES: 7597 persons from 10816 persons with a response rate of 70.2%; NS: 9047 persons from 11240 persons with a response rate of 80.5%). Most questions from the 1998 and 2005 survey are the same, while some were modified slightly or added to the 2005 survey. Among the particular variables we used for this study, the behavioral risk factors are in two- or three-point scale variables to allow equal comparison.