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Type of Question
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Example of Question
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Type of Evidencea
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Screening or early diagnosis
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Is prostate-specific antigen screening for the detection of prostate cancer in low-risk populations effective in reducing mortality?
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RCTs
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Does early diagnosis by use of a PETb scan result in improved cognitive ability for patients with Alzheimer’s disease?
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RCTs
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Etiology
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Does smoking cause lung cancer?
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Cohort studies, case-control studies
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Diagnostic accuracy
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Does a PET scan diagnose Alzheimer’s disease more accurately than a standard clinical evaluation?
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Case series (RCTs desirable but unlikely)
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Prognosis
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What is the likelihood for fertility loss in a premenopausal woman receiving chemotherapy for breast cancer?
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RCTs, cohort studies
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How long do patients remain insulin independent after pancreatic islet cell transplantation for Type I diabetes mellitus?
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Cohort studies, case series
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Preventive or therapeutic effectivenessc
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Is bevacizumab (Avastin) as effective as ranibizumab (Lucentis) in delaying the progression of acute macular degeneration?
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RCTs
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How does surgical implantation of an artificial lumbar disc compare with lumbar spinal fusion for pain reduction in patients with degenerative disc disease?
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RCTs
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Is external beam radiation more effective than watchful waiting in reducing mortality from prostate cancer?
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RCTs
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Safety or potential harm
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What proportion of postmenopausal women receiving calcium and vitamin D supplements develop kidney stones?
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RCTs, cohort studies, case-control studies
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Is robotic-assisted radical prostatectomy more likely to lead to urinary incontinence than laparoscopicic-assisted radical prostatectomy?
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RCTs, cohort studies, case-control studies
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aSystematic reviews of the “best” evidence are more reliable than evidence from a single study, regardless of the clinical question being asked.
bPET = positron emission tomography.
cIncludes drugs, devices, procedures, physical therapy, counseling, behavior change, and systems change in head-to-head comparisons and comparisons with standard interventions, placebo or sham treatments, or no intervention.
SOURCE: Adapted from the work of Dickersin (2007).
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