Abstract
This thesis addresses the object and methods of diagnostic test evaluation, focussing on the diagnosis of men with Lower Urinary Tract Symptoms (LUTS). The first part of this thesis serves as an introduction to this ill-defined disease, describing its etiology, prevalence, and clinical characteristics. The second part of the thesis covers issues of reproducibility. Multilevel regression analysis are used to study the variability in maximum urinary flow rate (Qmax) and pressure-flow studies in men with LUTS. Both of these frequently used diagnostic tests show poor reproducibility. The last part of the thesis deals with the object and methods of diagnostic research. It describes the traditional methods used to evaluate diagnostic tests, ranging from the calculation of sensitivity and specificity to likelihood ratios, ROC-curves, regression analysis, and neural network analysis.The traditional object of diagnostic research is the estimation of the prevalence of disease. Problems with diagnostic test evaluation will thus arise if the current state of medical knowledge does not permit measurement of the true disease state, i.e., if a gold standard is missing. In this thesis, the problem of a missing gold standard is discussed from a philosophical point of view. It is argued that the traditional methods of diagnostic tests identifying disease are based on a realist perspective of disease. Alternatively, a nominalist perspective does not distinguish between diseases and diagnostic tests; both are used to classify persons. Classifying patients is useful if it helps to predict their prognosis. Therefore, diagnostic test evaluation requires follow-up studies. Thus, a nominalist perspective of disease unifies diagnosis and prognosis into a single concept. The traditional gold standard test does not perfectly identify the disease state, but perfectly predicts treatment outcome instead. A missing gold standard test is not a drawback for diagnostic research.
