Contemporary work in medical decision support is characterized by a mu
ltitude of methods. To investigate their relative strengths and weakne
sses, we built four diagnostic expert systems based on different metho
ds (Bayes, case-based classification, heuristic classification) for an
alysis of the same set of 1254 cases of acute abdominal pain previousl
y documented in a prospective multicenter study. The results of the co
mparative evaluation indicate that differences in overall performance
are relatively small (statistically not significant). The performance
depends more on the quality of the knowledge base and the case data th
an on the inference methods of the expert systems. Methods relying exc
lusively on empirical knowledge (Bayes, case-based classification) ten
d to have slightly higher overall performance scores due to a diagnost
ic bias toward ordinary and common diseases. By contrast, methods oper
ating with expert knowledge (e. g., heuristic classification) perform
slightly worse overall, but are more sensitive toward uncommon (seriou
s) diseases.