1.1. Disease

To successfully develop tools which either quantify the rate of disease development in a population or quantify the factors which may contribute to disease occurrence, the “disease” of interest must be clearly defined. Broadly speaking, disease is any departure from perfect health. When applied to specific studies, a precise definition - the case definition - must be developed which unambiguously allows subjects to be classified as a case or not.

1.1.3. Positive and negative predictive values