- ARR Absolute risk reduction
- CI Confidence interval
- CV Coefficient of variation
- EBM Evidence-based medicine
- ER Event rate
- NiH Negativity in health
- NNT Number needed to treat
- PiD Positivity in disease
- QALY Quality-adjusted life year
- RCT Randomized controlled trial
- ROC Receiver-operating characteristic
- RRR Relative risk reduction
- USPSTF U.S. Preventive Services Task Force
The individual practitioner faces a multiplicity of potential diagnoses, limitations in diagnostic capacity, subclinical disease identified by tests rather than by clinical manifestations, and rapid changes in scientific knowledge. The paradigm of clinical decision-making based on the assumption that all that is needed to guide clinical practice is personal experience (however unsystematic), understanding of pathophysiology, and thorough training plus common sense is insufficient to address these challenges. Moreover, the integration of relevant research findings into clinical practice has been haphazard; the lag time between development of scientific knowledge and introduction into practice can be many years, and there is marked variation in practice. A systematic approach based on principles of clinical epidemiology can help address some of these issues. This quantitative approach has formed the primary, albeit not the only, basis of the evidence-based medicine movement. This movement posits that understanding certain rules of evidence is necessary to interpret the literature correctly and that physicians who practice based on the above understanding will provide superior care. This chapter will summarize some of the principles of clinical epidemiology and evidence-based endocrinology and some of their limitations.
Clinical epidemiology consists of the application of epidemiologic principles and methods to problems encountered in clinical medicine. Clinical epidemiology emphasizes a quantitative approach and is therefore concerned with counts of clinical events. Its applications are paramount (1) in diagnostic testing and how the results modify the probability of a particular disorder being present and (2) in treatment decisions in which the potential benefits and harms must be addressed. The techniques of clinical epidemiology have become increasingly important as practitioners confront the complexity of contemporary medical practice.
The appropriate choice and interpretation of diagnostic tests, whether biochemical assays, radiologic procedures, or clinical findings, have always been essential to the clinical practice of endocrinology. These tests, when introduced in the medical literature, are accompanied by varying degrees of validation. The clinician's assessment of the utility of tests, now even more important with the emphasis on cost-effectiveness, can be improved by knowledge of test EBM principles. We review some of these concepts as they apply to diagnosis and management of endocrine disorders, including the topics of test characteristics such as sensitivity and specificity, receiver-operating characteristic (ROC) curves, likelihood ratios, predictive values, and diagnostic accuracy.
The evaluation of endocrine function begins with a clinical question. The more vague the question, the more difficult it is to obtain a clear answer. Part of this step involves a clinical judgment about the likelihood of the disease prior to obtaining a test and its results. This pretest probability is combined with the performance characteristics of the ...