The Danish Health Interview Survey 2005 (SUSY) was conducted by the National Institute of Public Health [5]. The purpose of the survey was to describe the status and trends in health and morbidity in the adult population and the factors that influence health status, including health behavior and health habits, lifestyles, environmental and occupational health risks and health resources [5]. The study was based on a representative sample of 21,183 Danes aged 16 or older. The data was collected by personal interview in the respondent’s home followed by a self-administered questionnaire distributed after the interview [5]. The questions for both the interview [11] and the self-administered questionnaire [12] can be found elsewhere. There were 14,566 interviews conducted at a response rate of 66.7% and 11,238 self-administered questionnaires were returned at a response rate of 51.5% [5]. Using the SUSY 2005 data, a sample of 10,983 respondents aged 35 years or older was obtained; 17 were excluded because of missing data.

During the interview participants were asked two key questions, with subsequent follow-up questions. First they were asked, “Do you have any chronic disease, disorder or illness, chronic effects of injury, any functional impairment or any other chronic health problem?” If the answer was “yes”, then the participant was asked two follow-up questions: “What kind of disease?” and “Where in your body is the disease located?” The second key question asked them specifically, “Do you now or have you previously had a heart attack (myocardial infarction) or angina pectoris?”

Based on the interview responses the study sample was divided into three mutually exclusive groups:

• Participants with IHD: respondents giving a “yes” answer to one or both questions (n = 630);

• Participants with other chronic illnesses (e.g. musculoskeletal disease, respiratory disease, diseases of the nervous system) (n = 4353);

• Participants with no chronic illness (n = 5983).

All reported chronic illnesses were subsequently coded according to the International Classification of Diseases, 10th revision (ICD-10). The chronic illness breakdown is illustrated for both the IHD group and other chronic illness group in Table 1.

The other data collected can be categorized into seven major areas: sociodemographic, health behaviors, risk factors, healthcare system utilization, medication use, social relations and HRQoL. Standard socio-demographic data was collected during the interview including: gender, age, cohabitation status and educational level. The questions concerning health behaviors and risk factors included smoking pattern, level of physical activity, dietary intake, prevalence of hypertension and diabetes, use of preventive check-ups, self-efficacy [13] and height/ weight for BMI calculations.

Six questions in the interview addressed the use of physician services within the past three months and four questions asked about the use of other health-care providers within the same time period. Participants were also asked if they were regularly taking medication. Questions concerning quality of life included social relations, self-rated health, chronic activity limitations and self-rated HRQoL. There were three questions regarding social relations during the interview. Self-rated HRQoL measurement were collected from the self-administered questionnaire and based on the SF-36 [14,15]. Questions on sexual activity were also included in the self-administered questionnaire.

Raw prevalence and 95% confidence intervals are presented for the IHD group only. When comparing the three groups prevalences are adjusted for both age and gender and presented with 95% confidence intervals. To test for equal prevalences in the groups, a test for conditional independence [16] was used which takes into account the discrete nature of risk factors. All analyses were performed in SAS, version 9.1.

The comorbidities for the IHD group and the other chronic illness group are shown in Table 1. Some of the respondents in the IHD group reported other chronic illnesses in addition IHD. The IHD group’s most reported diseases included: musculoskeletal disease (23.6%); endocrine/metabolic disease (14.0%); respiratory disease (10.4%); nervous system disease (7.3%); and other injuries (5.0%). The other chronic illness group’s major chronic diseases are as follows: musculoskeletal disease (40.5%), endocrine/metabolic disease (13.0%), nervous system disease (12.7%), respiratory disease (12.4%) and other injuries (10.1%).

Health behavior and risk factors among people with IHD differed significantly from the two other groups (Table 2). The IHD group had fewer “never smokers” but more “smokers” and “former smokers” compared to the other two groups (p < 0.001). The IHD group is more sedentary and participating in less in heavy physical activity, however there is little difference between the three groups in regards to self-reported moderate physical activity. Dietary behavior also did not differ between the groups. Obesity, as represented by BMI, was significantly more prevalent in the IHD group (26.0%; (95% CI: 20.5% - 31.5%)) than in the group with other chronic illness (15.8%; (95% CI: 14.7% - 16.9%)) and the group without illness (9.6%; (95% CI: 8.8% - 10.4%)) (p < 0.001). Furthermore, people with IHD had lower selfefficacy (confidence that their own effort is important in staying healthy [12]). Attendance for preventive health check-ups was significantly more frequent in the IHD group (87.8%); (95% CI: 84.1% - 91.5%) than in the group with other illness (70.6%); (95% CI: 69.2% - 71.9%) and in the group with no illness (54.2%); (95% CI: 53.0% - 55.5%) (p < 0.001). Similar patterns were seen for blood pressure and cholesterol preventive visits. Hypertension and diabetes, which are well-known risk factors for IHD, were significantly more prevalent in the IHD group compared to the other two groups.

Health-care utilization varied considerably between the two disease groups and the group without disease (Table 3). Use of general practitioners, outpatient clinics and hospitalization was significantly more frequent in the IHD group than in the group with other chronic illness. A total of 84.4% of the IHD group stated that they regularly or continually took medicine and this proportion was significantly higher than the chronic illness group (69.7%) and the group without illnesses (26.7%).

Table 4 shows various indicators of HRQoL including social relations, self-rated health, chronic activity limitations, self-rated HRQoL and sexual activity. Both the IHD group and the group with other illnesses had significantly poorer social relations than people without illness. The IHD group also rated their own health as significantly poorer than the two other groups and the groups with illness reported more activity limitations than the group without illness.