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INTRODUCTION

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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
NNH Number needed to harm
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

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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 (EBM) 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 summarizes some of the principles of clinical epidemiology and evidence-based endocrinology and some of their limitations.

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CLINICAL EPIDEMIOLOGY

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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.

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DIAGNOSTIC TESTING: TEST CHARACTERISTICS

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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.

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The evaluation of endocrine function begins with a clinical question. The more vague the question, the more difficult it is to obtain a ...

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