How to Critically Appraise an Article

Summary and Introduction

Summary

Critical appraisal is a systematic process used to identify the strengths and weaknesses of a research article in order to assess the usefulness and validity of research findings. The most important components of a critical appraisal are an evaluation of the appropriateness of the study design for the research question and a careful assessment of the key methodological features of this design. Other factors that also should be considered include the suitability of the statistical methods used and their subsequent interpretation, potential conflicts of interest and the relevance of the research to one's own practice. This Review presents a 10-step guide to critical appraisal that aims to assist clinicians to identify the most relevant high-quality studies available to guide their clinical practice.

Introduction

To practice evidence-based medicine, clinicians need to apply the findings of scientific research to the circumstances of individual patients as part of their clinical decision-making process. Clinicians, therefore, must be able to select and appraise scientific literature that is relevant to their field, understand the implications of research findings for individual patients, elicit patients' own preferences and develop an appropriate management plan based on the combination of this information. Each of these tasks presents its own challenges, but the sheer volume of medical literature means that the first step (that of selecting and appraising scientific evidence) can be daunting. The number of new medical research articles published each year continually increases, and more than 12,000 new articles, including papers on in excess of 300 randomized controlled trials (RCTs), are added to the MEDLINE database each week.^[1,2] One practical way that clinicians can manage this 'information overload'^[2] is to develop efficient skills in critical appraisal, which enable them focus on only the highest-quality studies that will guide their clinical practice and to extrapolate information when necessary from studies of less rigorous design if high-quality trials are unavailable.

Critical appraisal has been defined as the "...application of rules of evidence to a study to assess the validity of the data, completeness of reporting, methods and procedures, conclusions, compliance with ethical standards, etc. The rules of evidence vary with circumstances."^[3] Although the methodological criteria by which the validity of a study is assessed will vary according to its design, some general principles underpin the evaluation of any research study. Various guidelines and assessment tools have been developed to provide a structured approach to the process of critical appraisal for clinicians.^{[4,5,6,7,8,9,10,11,12,13,14]}

Despite the plethora of documents available to guide the process, no 'gold-standard' instrument for critical appraisal exists. The criteria used to assess the validity and relevance of scientific literature are not static; they must evolve with improvements in understanding of the important sources of bias inherent in different study designs, and increased awareness of the potential influence of other nonmethodological factors, such as conflicts of interest.^[15] A structured approach to critical appraisal could potentially improve the quality of this process, and simple checklists can be useful to screen out research that is of low quality or of little relevance.^[16] This Review presents a guide to the critical-appraisal process.

Cite this: How to Critically Appraise an Article - Medscape - Feb 01, 2009.

Box 1. Ten Questions to Ask when Critically Appraising a Research Article
Is the study question relevant? Does the study add anything new? What type of research question is being asked? Was the study design appropriate for the research question? Did the study methods address the most important potential sources of bias? Was the study performed according to the original protocol? Does the study test a stated hypothesis? Were the statistical analyses performed correctly? Do the data justify the conclusions? Are there any conflicts of interest?

Box 2. Key Methodological Points to Consider in the Appraisal of Systematic Reviews and Meta-analyses
Were all relevant studies included (i.e. was the search comprehensive, did it exclude articles on the basis of publication status or language and was the potential for publication bias assessed)? Were selected articles appraised and data extracted by two independent reviewers? Was sufficient detail provided about the primary studies, including descriptions of the patients, interventions and outcomes? Was the quality of the primary studies assessed? Did the researchers assess the appropriateness of combining results to calculate a summary measure?

Box 3. Key Methodological Points to Consider in the Appraisal of Randomized Controlled Trials
Was the process of treatment allocation truly random? Would participants have been able to know or guess their treatment allocation? Were participants and researchers 'blinded' to participants' treatment group? Were outcomes assessed objectively? Were all participants who were randomly allocated a treatment accounted for in the final analysis? Were all participants' data analyzed in the group to which they were randomly allocated?^a ^aSee section on intention-to-treat analysis under 'Were the statistical analyses performed correctly?'

Box 4. Key Methodological Points to Consider in the Appraisal of a Cohort Study
Is the study prospective or retrospective? Is the cohort representative of a defined group or population? Were all important confounding factors identified? Were all important exposures and/or treatments, potential confounding factors and outcomes measured accurately and objectively in all members of the cohort? Were there important losses to follow-up? Were participants followed up for a sufficient length of time?

Box 5. Key Methodological Points to Consider in the Appraisal of a Case-Control Study
Were the cases clearly defined? Were the cases representative of a defined population? How were the controls selected and were they drawn from the same population as the cases? Were study measures identical for cases and controls? Were study measures objective or subjective and is recall bias likely if they were subjective?

Box 6. Key Methodological Points to Consider in the Appraisal of a Cross-sectional Study
Was the study sample clearly defined? Was a representative sample achieved (e.g. was the response rate sufficiently high)? Were all relevant exposures, potential confounding factors and outcomes measured accurately? Were patients with a wide range of severity of disease assessed?

Box 7. Key Methodological Points to Consider in the Appraisal of a Case Study
Were cases identified prospectively or retrospectively? Are the cases a representative sample (e.g. a consecutive series of individuals recruited from multiple centers) and similar to patients in your practice? Were all relevant exposures, potential confounding factors and outcomes measured accurately?

Box 8. Key Methodological Points to Consider in the Appraisal of a Study of Diagnostic Accuracy
Does the sample of patients represent the full spectrum of patients with and without the diagnosis of interest? Was there a comparison with an appropriate 'gold-standard' test? Did all patients receive both the test under evaluation and the same 'gold-standard' test? Were the tests performed independently with blinding of assessors to the results of the 'gold-standard' test? Were the cut-offs that were used to classify patients as having a positive test result clearly described?

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How to Critically Appraise an Article

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