BMC Public Health 2007, 7:277 http://www.biomedcentral.com/1471-2458/7/277 number of people correctly classified as diabetes or not) for determining whether that RF (i.e., "abdominal obes- ity" or "high BMI") was present. Odds ratios around the threshold were stable. The ROC analysis was done to determine diabetes-specific thresholds for obesity (BMI) and abdominal obesity (waist circumference) rather than using the continuous variable for these factors; and the ROC model with the continuous variables was only slightly improved over the dichotomous variable. The sensitivity of the model predicting diabetes (duration ≥ 3 years) was 0.63 (range = 0.61–0.70) and specificity was 0.80 (range = 0.75–0.82). Analyses of the areas under the ROC curves for abdominal obesity found an optimal cut- off value at waist circumference ≥ 97 cm for men and waist circumference ≥ 89 cm for women. For BMI, the optimal threshold value was ≥ 28 kg/m2 in both men and women. RF levels were calculated as the unweighted number of RFs reported by each respondent on the screening ques- tionnaire. For example, if a person reported three RFs on the screening questionnaire, they were classified into RF level 3. Most analyses of the SHIELD BL data reported here grouped individuals into cohorts with lower risk (0–2 RFs) or higher risk (3–5 RFs). Data reported here reflect the sociodemographic characteristics of the respondents to the BL survey and the occurrence rates of each RF among our respondent subgroups. Results Response rates and analyzed cohort Of the 200,000 households that received the screening questionnaire, 127,420 households (containing a total of 211,097 adults) returned usable questionnaires, yielding a response rate of 63.7% for the screening survey. The fol- low-up BL survey was mailed to a total of 22,001 individ- uals, and 17,640 were returned, for a response rate of 80.2%. The total number of usable (i.e., no missing val- ues) returns was 15,794 (71.8%). Prevalence of diabetes mellitus and risk factors The SHIELD screening survey revealed that the overall prevalence of self-reported diagnosis of DM (either type 1 or type 2) was 8.2% for the 211,097 respondents, with increased prevalence with increasing age (Table 1). In comparison, the overall DM prevalence in NHANES for self-report was 6.5% and 9.0% for self-report and clinical and laboratory evaluations, with approximately 2.5% of the 9.0% undiagnosed. The prevalence estimates for each of the 5 RFs, as found in the SHIELD and NHANES studies, are also shown in Table 1. The estimated proportions of the population with BMI ≥28 kg/m2 (obese) and history of CVD events were gener- ally similar in SHIELD and NHANES, while the preva- lence of abdominal obesity and of dyslipidemia estimated in SHIELD were lower than from NHANES. Table 1: Prevalence of diabetes mellitus and risk factors in the SHIELD screening and NHANES 1999–2002 studies by age and gender Condition Diabetes mellitus Age 18–44 Age 45–64 Age 65+ Dyslipidemia Total cholesterol LDL-C HDL-C Triglycerides Abdominal obesity BMI≥28 kg/m2 Hypertension History of cardiovascular event Prevalence from: SHIELD self-report NHANES overall All Men Women All Men Women 8.2 25.8 17.1 9.5 5.0 6.7 31.5 40.0 23.4 6.6 8.5 3.0 12.9 20.3 26.9 18.0 10.4 5.5 7.5 27.9 40.9 23.0 8.0 7.9 2.9 11.3 16.6 24.8 16.3 8.7 4.5 6.0 34.8 39.2 23.8 5.3 9.0 52.9 34.8 13.7 23.7 16.9 51.4 40.9 28.9 6.9 10.2 4.4 15.8 20.6 60.2 35.9 15.2 34.1 20.5 50.8 40.5 27.0 8.0 7.8 3.2 9.6 17.1 45.8 33.7 12.3 13.4 13.5 51.9 41.4 30.8 5.8 LDL-C = low-density lipoprotein cholesterol, HDL-C = high-density lipoprotein cholesterol, BMI = body mass index Page 4 of 9 (page number not for citation purposes)