CRITICAL APPRAISAL SERIES
Critical appraisal for emergency medicine 3: Evaluation of a therapy
Correspondence to:
Professor S Goodacre, Medical Care Research Unit, University of Sheffield, Regent Court, 30 Regent Street, Sheffield S1 4DA, UK; s.goodacre@sheffield.ac.uk
Accepted 6 January 2008
| The first 150 words of the full text of this article appear below. |
Evaluation of a therapy involves comparing a group of patients receiving the intervention with a group of patients who do not receive it (the control group). With a few rare exceptions (such as diseases that currently have 100% mortality), a control group is always required to demonstrate that any improvement observed after treatment is not simply due to the natural course of the illness. There are a number of key elements in the design of these studies that will determine whether the findings are valid and generalisable.
SELECTION AND ALLOCATION OF STUDY PARTICIPANTS
Patients are selected to a trial by a process of recruitment that usually involves identification of potential participants, assessment of eligibility using inclusion and exclusion criteria, followed by a request for consent to participate. Selection can occur at any of these stages to influence the constitution of the study population. This is obviously a necessary process in assembling the study population, but selection
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