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A primary goal for clinicians is to evaluate the benefits and harms from the treatment options before them. Primum non nocere is a basic principle of ethical practice. “Evidence-based medicine is the conscientious, explicit, and judicious use of the current best evidence in making decisions about the care of individual patients. The practice of evidence-based medicine means integrating the individual clinical expertise with the best available external evidence from systematic review.”1 Since the 1990s, evidence-based medicine (EBM) has been gaining a strong foothold in most disciplines of medicine. In order to practice EBM, however, it is paramount that clinicians are capable of assessing and synthesizing medical literature. Effective physicians comprehend the balance between personal clinical experience and evidence from appropriately conducted research. Clinicians need to proficiently assess the quality of published studies with respect to design, conduct, and analysis, and then to determine the relevance and external validity to their specific patient. Not all evidence is equal, nor does it offer definite clinical plans of care. One needs to understand the basic threats to the validity of studies, namely bias, confounding, and chance. The randomized controlled trial (RCT) and meta-analysis are regarded as the gold standard of EBM. However, RCTs are difficult to perform in critical care medicine.

Critical care medicine is a rapidly evolving discipline that deals with a complex disease spectrum. Sepsis and ARDS, for example, are still poorly understood disease processes with multiple etiologies and phenotypes. Sepsis syndrome may arise from a number of sources all presenting differently in different patients. Consequently, there are many challenges in the conduct of sound clinical research in this field: critical illness is difficult to precisely define; patient populations may differ drastically with respect to severity of disease, treatment modalities, and other characteristics; subject recruitment may be difficult.

A sound knowledge of fundamental statistics will lay the basis for critical appraisal of the literature, an imperative clinical tool in every practitioner’s armamentarium. Statistical tools can be used to describe the performance of diagnostic tests, characterize relationships between clinical decisions and outcomes, and estimate survival probabilities, just to name a few of their many uses. Ultimately, one would like to pair a critical appraisal of evidence with comprehensive clinical judgment at the bedside, where n = 1.


Perhaps as important as an understanding of the methods of analysis used in clinical studies is an understanding of the various types of study designs, their defining characteristics, and the strengths and weaknesses of each. The most commonly used designs that involve collection and analysis of original data (“primary studies”) can be broken into 2 subtypes: experimental or intervention studies and observational studies. Yet another class of studies (“secondary studies”) seeks to synthesize information from multiple existing studies of the same research question. For experimental designs, we describe the RCT and other clinical trial designs. For observational studies, we ...

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