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    The literature on a topic of clinical interest often includes conflicting or inconclusive studies, thereby requiring the development of critical skills for interpreting the results.
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    A systematic approach to evaluating the features of individual studies can provide thoroughness and consistency to a review of the literature.
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    The evaluation of an individual study should include the research hypothesis, the study design, the predictor and outcome variables, the methods of analysis, possible sources of bias, and interpretation of results.
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    In considering whether a statistical association is likely to represent a causal relationship, one should consider the strength of the association, the presence of a dose-response trend, correct timing of events, consistency across studies, and biological plausibility.
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    A meta-analysis is a quantitative systematic review in which the results of multiple studies are combined to obtain a precise, and hopefully unbiased, estimate of the association under study.

image A 40-year-old accountant visited her family physician for a routine checkup. The patient’s mother had been diagnosed with breast cancer in the past year, and the patient wanted advice about what she could do to reduce her own risk of developing this disease. The patient had two children aged 6 and 8 years. She was in good health, with regular menstrual cycles, and she had a recent normal Papanicolaou smear and mammogram.

In responding to the patient’s questions about breast cancer, the physician confirmed that a positive family history increases the risk of developing this disease. A number of other characteristics are associated with a reduced risk of developing breast cancer, such as early age at first full-term pregnancy and increasing number of pregnancies. Unfortunately, these factors are not easily susceptible to intervention, and the patient already had completed her childbearing. The physician was also aware of a controversy regarding the relationship between the intake of dietary fat and the occurrence of breast cancer. Before recommending that the patient reduce her fat intake, however, the physician wished to review the pertinent medical literature.

The recommendations that physicians make to patients depend on the current state of knowledge available about diseases, the underlying pathophysiology of diseases, and the most effective treatment for diseases. The knowledge base of clinical medicine is continuously expanding, and physicians must therefore develop methods to seek out and apply new information.

image This process is complicated when inconclusive or conflicting results are found in the medical literature. The publication of articles, even in the most respected journals, does not guarantee that the investigators’ conclusions are valid, or even if valid, relevant to the daily practice of a particular physician. The history of medicine includes countless examples of therapies that were once widely accepted but later were shown to be ineffective or even harmful to patients. Clinicians must develop skills that will allow them to update and reevaluate their knowledge, enabling them to provide optimal patient care.

The first step in acquiring new medical knowledge is to ...

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