No objective classification criteria for atopic dermatitis (AD) exist. Therefore the diagnosis is usually based on many variables including anamnestic, clinical, and laboratory findings. The aim of this study was to develop and validate a diagnostic score to standardize the diagnosis of atopic skin diathesis for clinical and epidemiological studies. In two separate studies, each consisting of cases and controls, 19 atopic binary features were examined by two independent experienced physicians and these features were classified as ''objective,'' respectively, ''subjective.'' On the basis of these criteria and two additional laboratory measures, we developed a score with high discriminative ability, using the logistic regression model and backward elimination. Ignoring ''subjective'' variables and the two laboratory measures, two additional models were built that had a worse fit in the original data, but still yielded high estimates of sensitivity (similar to 90%) and specificity (similar to 96%). Using the same data as for the model building, it is well known that these estimates are too optimistic. The validation study allows us to obtain unbiased estimates of sensitivity and specificity for the different scores and to investigate the influence of data quality-here given by the assessment of the reproducibility of the features (objective and subjective)-on the usefulness of diagnostic scores. The results of the validation study show that we developed simple and easy-to-use scores offering a base for a broad practical use in epidemiological and clinical research. In addition, we demonstrate that the criteria classified as ''subjective'' have no influence on the case control status in the validation study.
