Rate of Missing Socioeconomic Factors in the 4th KNHANES

This study is to assess how missing values in socioeconomic status (SES) variables were handled in the Korean Journal of Family Medicine (KJFM) article using the Korea National Health and Nutrition Examination Survey (KNHANES) data and to estimate the rate of missing SES variables from the 4th KNHANES. We searched all original articles published in the KJFM from 2007 to 2011 and identified those that used KNHANES as their primary source of data. None of the 11 articles which presented KNHANES SES variables took into account of omitions in the analysis. The estimated rate of missing data on education, household income, marital status, and occupation data of the 4th KNHANES was 0.3 (0.05)%, 2.7 (0.2)%, 0.5 (0.1)%, and 9.4 (0.9)%, respectively. When all four variables were used simultaneously, the rates increased to 11.8 (0.9)%. Respondents with missing household income tended to be older (P < 0.001), less educated (P < 0.001), and more likely to be unemployed (P < 0.001), and widowed (P < 0.001). A similar relationship was shown for missing occupation data. Omissions in SES variables in KNHANES were related to certain characteristics of study participants. Researchers using KNHANES data should keep in mind the possible bias which can be introduced by missing SES values.