Stichproben in der ambulanten Qualitätssicherung am Beispiel der Koloskopie

Abstract

Sampling inspections are an approved instrument for assuring and promoting the quality of healthcare. Individual documentations of medical services are requested from physicians and randomly selected for quality rating by experienced peer reviewers. For example, sampling inspections are stipulated by law for certain ambulatory services (e.g., colonoscopies) delivered by SHI-authorised physicians in order to maintain professional performance standards of colonoscopists. On behalf of the regional Association of Statutory Health Insurance Physicians (ASHIP) experienced colonoscopists regularly rate selected visual documentations (videotapes, photographs) of colonoscopies performed by SHI-authorised physicians in the ambulatory care sector. For anatomical reasons, however, a certain proportion of colonoscopies of inadequate quality will generally be tolerated. Whenever this value is exceeded, ASHIP may impose sanctions against the physician. The question is how sampling inspections have to be performed and dimensioned in order to ensure that the tests be sufficiently meaningful in terms of sensitivity and specificity. Relevant sampling test parameters such as the false-positive rate (physicians are wrongly accused of inadequate quality) and the false-negative rate (existing deficiencies are not identified) are calculated. The calculations are performed analytically or, in the case of complex sampling test scenarios, numerically by means of computer simulations. The calculations show that single-stage sampling tests usually do not result in acceptable values for the false-positive and the false-negative rates. For example, a sampling test which requires the documentation of 20 colonoscopies will -- assuming some reasonable tolerance of inadequately performed colonoscopies -- result in a false-positive rate of 6% and a false-negative rate of 47%. The false-positive-rate, which is particularly relevant from a legal point of view, can be reduced by providing a two-stage sampling test. A significant reduction of the false-negative-rate may be achieved by (multiple) repetition of the single-stage sampling test and consideration of cumulative probabilities. In principle, sampling inspections permit statements in terms of probabilities only. In sampling inspections of healthcare quality false-negative rates are usually considered, i.e., the probability that the test is unable to identify existing quality deficiencies. However, false-positive rates also need to be considered in cases where sanctions may be imposed against the physician on the basis of a positive sampling test. Numerical calculations of false-positive and false-negative rates for simple and complex sampling test scenarios should be performed in order to choose the optimum procedure and dimension of a sampling test.