A COMPREHENSIVE CLINICAL EPIDEMIOLOGIC THEORY-BASED ON THE CONCEPT OFTHE SOURCE PERSON-TIME AND 4 DISTINCT STUDY STAGES

The medical community is forced to accelerate the move from opinion-ba sed to evidence-based medicine, that is, to aim at basing all caring a nd clinical practice on empiri. A clear-cut epistemology would facilit ate this process. In this article we present a comprehensive clinical epidemiological theory which can be used for validity issues in caring science, quality of life research, controlled clinical trials and com pilations of uncontrolled evidence. The theory is based on four distin ct stages that can be identified in a study, whereof the first is dema rcation of the source person-time. A source person-time ('study base') can be identified for any study in all disciplines, giving an argumen t for using this concept as the common reference point for validity is sues. Apart from identifying the source person-time, recovery of the a ctually observed person-time, collection of data and calculation of an ('adjusted') effect parameter (e.g., incidence ratio) are additional stages of a study. When the source person-time is demarcated confoundi ng is introduced, when the actually observed person-time is recovered misrepresentation, in the third stage misclassification and in the fou rth analytical alteration of the parameter of effect. The concept of t he source person-time can, in addition, link examination of validity i n caring and clinical sciences to observational studies. thereby allow ing the field to benefit from all theoretical achievements for prevent ing, handling and understanding systematic errors developed in epidemi ology. We conclude it is possible to implement a common terminology of validity for all caring and medical sciences. Drawing causal inferenc es in these disciplines is not mechanical, it can never, for example, be done with statistical inference. Establishing a causal relation alw ays includes an assessment of the magnitude and direction of systemati c errors influencing the adjusted effect parameter. From the presented epistemology it follows that differences in validity from a case hist ory to a large randomized, placebo-controlled and double-blinded study are quantitative rather than qualitative. This realization in turn op ens up for a more refined discussion of when a decision is evidence-ba sed rather than opinion-based.