Original ArticleHigh agreement of self-report and physician-diagnosed somatic conditions yields limited bias in examining mental–physical comorbidity
Introduction
Over the last few years, the association between somatic diseases and mental disorders has received increasing attention as a focus of research. Based on large-scale epidemiological surveys on mental health prevalence rates, comorbid mental disorders in patients with several somatic diseases have been examined [1], [2], [3], [4], [5], [6], [7], [8], [9]. Recent reviews have shown that comorbid mental disorders are associated with increased mortality and morbidity, intensified health care utilization and lowered quality of life in patients with chronic somatic diseases [10], [11], [12], [13], [14]. A precondition of these research activities is the use of a reliable and valid instrument for recording mental disorders, such as the Composite International Diagnostic Interview (CIDI) [15]. Such types of standardized interviews can be regarded as the gold standard for assessing mental disorders, and are thought to overcome the validity problems of mental disorder assessments used in the past [16].
Studies on the prevalence rates of mental disorders in patients with vs. without a somatic disease emphasize the importance of a valid assessment of mental disorders. The operationalization of the index disease, however, is often based solely on patients' self-reports [4], [5], [6], [7], [8], [9]. Although there are studies which reported at least moderate to high agreements, for example, diabetes [17], [18], [19], [20], [21], [22], [23], coronary heart diseases [18], [19], [20], [21], [22], [23], [24], or cancer [18], [19], [22], the reliability and validity of self-reported somatic disease status proved to be limited for diseases, such as arthritis [19], [20], other cardiovascular diseases [17], [18], [19], [20], [21], [22], or lung diseases [18], [20], [22]. As a result, the measurement errors in index diseases may lead to biased estimates of prevalence rates of comorbid mental disorders [25].
The present study aims to quantify the misclassification bias of self-reported somatic diseases and to predict the impact of this bias on the estimation of comorbidity with mental disorders based on eight frequent, chronic somatic diseases: coronary heart disease (CHD), heart failure, asthma, chronic bronchitis, non–insulin-dependent diabetes, cancer, arthrosis, and arthritis. For this purpose, data from the German National Health Interview and Examination Survey (GHS) were used [26], which assessed both self-reported and physician-diagnosed somatic diseases. The following questions will be answered.
- 1.
What are the misclassification rates of self-reported somatic diseases?
- 2.
What are the sociodemographic and medical correlates of the misclassification rates of self-reported somatic diseases?
- 3.
To what extent are mental comorbidity estimations in patients with vs. without a somatic disease biased when they are based on self-reports of somatic diseases rather than physicians' diagnoses?
Section snippets
Study design and samples
Data were drawn from the GHS, a stratified, multistage, cross-sectional, nationally representative sample of subjects aged 18–79 years from the noninstitutionalized population of Germany. Aims, design, and methods have been described in greater detail in a separate publication [26]. Therefore, design and sample characteristics are discussed only briefly here.
The GHS consisted of a stratified random sample from 113 communities throughout Germany with 130 sampling units. A representative gross
Misclassification rates of self-reported somatic diseases
The agreement rates between self-reported and formally diagnosed disease cases are reported in Table 2. The specificity (92.76–99.70%) and the NPV (94.52–99.73%) proved to be very high for all somatic diseases. The sensitivity was lowest for arthritis (84.45%) and highest for asthma (94.99%). A misclassification of self-reported and formally diagnosed cases was most frequent for the condition of a false-positive disease status report. The PPV was lowest for arthritis, at 42.26%, and highest for
Discussion
The present study examined the impact of a misclassification of patients with somatic diseases based on self-report data on risk calculations of comorbid mental disorders. Most large-scale epidemiological studies that have analyzed the association of somatic and mental comorbidities were based on self-reported somatic disease status [4], [5], [6], [7], [8], [9]. Those studies have often become landmark studies determining future research efforts and public health topics, making it all the more
Acknowledgments
We would like to thank the Max Planck Institute for Psychiatry and the Department of Psychology and Psychotherapy of the TU Dresden for providing the GHS-MHS survey data [34] and the Robert Koch Institute for providing the GHS-CS survey data [35].
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