QUADAS-2: A Revised Tool for the Quality Assessment of Diagnostic Accuracy StudiesFREE
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Abstract
Methods
Define the Scope
Review the Evidence Base
Hold a Face-to-Face Consensus Meeting
Pilot and Refine
Role of the Funding Source
QUADAS-2
Phase 1: Review Question
Phase 2: Review-Specific Tailoring
Phase 3: Flow Diagram
Phase 4: Judgments on Bias and Applicability
Risk of Bias
Applicability
Domain 1: Patient Selection
Risk of Bias: Could the Selection of Patients Have Introduced Bias?
Applicability: Are There Concerns That the Included Patients and Setting Do Not Match the Review Question?
Domain 2: Index Test
Risk of Bias: Could the Conduct or Interpretation of the Index Test Have Introduced Bias?
Applicability: Are There Concerns That the Index Test, Its Conduct, or Its Interpretation Differ From the Review Question?
Domain 3: Reference Standard
Risk of Bias: Could the Reference Standard, Its Conduct, or Its Interpretation Have Introduced Bias?
Applicability: Are There Concerns That the Target Condition as Defined by the Reference Standard Does Not Match the Question?
Domain 4: Flow and Timing
Risk of Bias: Could the Patient Flow Have Introduced Bias?
Incorporating QUADAS-2 Assessments in Diagnostic Accuracy Reviews
Discussion
Appendix: The QUADAS-2 Group
Supplemental Material
References
Information & Authors
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Keywords
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Authors
Metrics & Citations
Metrics
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QUADAS-2: A Revised Tool for the Quality Assessment of Diagnostic Accuracy Studies. Ann Intern Med.2011;155:529-536. [Epub 18 October 2011]. doi:10.7326/0003-4819-155-8-201110180-00009
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Significant Improvement but some Minor Adjustments Still Needed
The recent article by Whiting et al1. on QUADAS-2 describes some important changes over the old version of QUADAS2. I recently completed a manuscript using QUADAS-2 and encountered a few issues regarding the grouping of items and would appreciate the authors' comment.
The question on progression bias has now been moved to the domain on timing and patient flows. While progression bias and patient flows both involve the dimension of time, it seems that progression bias fits more naturally with bias and applicability of the reference test. The timing of the reference test relative to the index test can be viewed as a design parameter of the reference test. An inappropriate interval can lead to bias (disease progression bias or positive misclassification due to new disease in an inappropriately long interval, or negative misclassification due to an inappropriately short interval). Differences in the interval between tests might affect applicability of the reference test. Inadequate reporting of the interval would make it difficult to determine the applicability of the reference test. Thus, it seems that the question relating to the time interval is might fit more naturally with the reference test domain.
Domain 3 (Flow and Timing) focuses on accounting for all the events and results associated with each patient. A study should account for all those who received or were referred to receive the index test. Indeterminate results are part of this accounting and it would seem that indeterminate results would be a natural part of Domain 3. Unfortunately, the question QUADAS on indeterminate results from the old version of seems to have been moved to the domain on patient selection where it is viewed as an issue of patient selection (excluding "difficult to classify cases). Alternatively, one might view the handling and reporting of indeterminate results as related to the applicability of a test. The issues related to indeterminate results can be important and it is unclear why this item was dropped.
Similarly, two questions from the old QUADAS (partial verification bias, withdrawals) appear to have been lumped into a single item in QUADAS -2. It might be useful to keep these separate because they may represent different risks to bias and it can be helpful to provide estimates of the degree of risk from either source. Also, it may be helpful to show whether deficiencies are related to study design issues (partial verification bias) or study implementation (withdrawals).
Overall, I found QUADAS-2 to be a significant improvement over the old version. In particular, the new survey has been improved by the conceptual separation of bias and applicability. Still, it seems that the survey may be improved by some minor adjustments.
Robert Schmidt Department of Pathology University of Utah
REFERENCES:
1. Whiting PF, Rutjes AWS, Westwood ME, et al. QUADAS-2: A Revised Tool for the Quality Assessment of Diagnostic Accuracy Studies. Annals of Internal Medicine. October 18, 2011 2011;155(8):529-536.
2. Whiting P, Rutjes AWS, Reitsma JB, Bossuyt PMM, Kleijnen J. The development of QUADAS: a tool for the quality assessment of studies of diagnostic accuracy included in systematic reviews. BMC Med Res Methodol. 2003;3:25.
Conflict of Interest:
None declared
Re: Quality Assessment of Diagnostic Accuracy Studies - The Revised QUADAS-2 Tool
We thank Drs Dewey, Schueler and Schuetz for their comments regarding our recent publication(1) and are grateful for the opportunity to comment on the important issues they raise.
It is not strictly correct that items 1 and 2 of the original QUADAS tool(2) relate to variability (external validity). Item 1 covers both bias (in patient selection) and variability (of included patients), while item 2 relates solely to reporting quality. Distinguishing between risk of bias (internal validity) and applicability (external validity) was key to developing QUADAS-2. Assessment of applicability requires a clear definition of the patients, tests and target condition of interest. Dewey et al suggest that applicability should be assessed in relation to "patients in practice" rather than the review question, as all included studies should be applicable to the review question. If there is an exact match between the review question and inclusion criteria then this is correct. However in practice inclusion criteria are often broader than the review question. We do not think it feasible to assess applicability in relation to "patients in practice", because the test may be applied to multiple patient groups, and there may be different test variants or definitions of the target condition.
Dewey et al believe that completing QUADAS-2 may be more time consuming and asked about the average time to evaluate a study using QUADAS-2, compared to the original tool. A user survey (www.bris.ac.uk/quadas/resources/quadas2reportv4.pdf) found that completing the original tool takes from <10 minutes to 1-2 hours. We do not have such data for QUADAS-2, but from personal experience find that completing QUADAS-2 takes around 10 minutes in addition to data extraction although this is likely to vary considerably based on reviewer experience and the review topic. There were no negative comments regarding the time taken to complete the assessment during piloting.
We hope to make worked examples of QUADAS-2 assessments and more detailed domain specific guidance available on www.quadas.org in the near future. An explanatory paper is not currently planned, although we are working on updating the quality assessment chapter in the Cochrane Handbook for Diagnostic Test Accuracy reviews to include QUADAS-2; this will include more detailed guidance.
We believe that agreement at the domain level is a key concern. Variability in scoring signaling questions is only important if it affects the overall risk of bias rating, because these, not answers to signaling questions, will be reported in the review.
Penny Whiting and Jonathan Sterne on behalf of the QUADAS-2 group
References:
1. Whiting PF, Rutjes AW, Westwood ME, Mallett S, Deeks JJ, Reitsma JB, et al. QUADAS-2: A Revised Tool for the Quality Assessment of Diagnostic Accuracy Studies. Ann Intern Med. 2011;155(8):529-36.
2. Whiting P, Rutjes AW, Reitsma JB, Bossuyt PM, Kleijnen J. The development of QUADAS: a tool for the quality assessment of studies of diagnostic accuracy included in systematic reviews. BMC Med Res Methodol. 2003;3:25.
Conflict of Interest:
None declared
Quality Assessment of Diagnostic Accuracy Studies - The Revised QUADAS-2 Tool
It was with great interest that we have read the recent article by Whiting et al. introducing the QUADAS-2 tool (1), that revises the QUADAS tool from 2003 (2). It is important that such pivotal methodological work about diagnostic review research is made widely available by publication in the Annals of Internal Medicine.
We would like to discuss some issues related to QUADAS-2 as some of them attracted our attention when reading the otherwise impressive article:
1) In the original QUADAS tool (2), items 1 and 2 related to variability with the potential to affect clinical generalizability (external validity) of study results. Commonly, the term "applicability" is used as a synonym for this (3). But, in QUADAS-2, "applicability" refers to whether or not certain aspects of an individual study are matching or not matching the review question (1). When conducting a systematic review, the review question (e.g., according to PICOS (4)) and eligibility criteria are pre-specified before systematically searching for relevant studies (5). Therefore, all studies reaching the stage of quality assessment in a systematic review should be applicable to the review question since studies not matching the review question and eligibility criteria have been sorted out already during the selection process. The use of applicability in QUADAS (2) as the "degree to which the results of a study can be applied to patients in practice" may thus be preferable.
2) Some aspects of QUADAS-2 seem to be more time consuming (e.g., drawing a flow-chart for each study). What is the average time needed to evaluate a study using QUADAS-2 versus QUADAS?
3) The mentioned examples of study assessment, that would facilitate understanding QUADAS-2, are not yet available from www.quadas.org. Also, an explanation paper further describing the use in detail would be very helpful for researchers conducting diagnostic accuracy meta-analyses. Is this planned?
4) Calculating the interrater reliability only for agreement on the domain level when piloting the tool may not be appropriate to detect variability on the level of signalling questions, which however are used for the important decision on whether high or low risk of bias is present in individual studies.
We would greatly appreciate the authors' comments on these issues.
References:
1. Whiting PF, Rutjes AW, Westwood ME, Mallett S, Deeks JJ, Reitsma JB, et al. QUADAS-2: A Revised Tool for the Quality Assessment of Diagnostic Accuracy Studies. Ann Intern Med. 2011;155(8):529-36.
2. Whiting P, Rutjes AW, Reitsma JB, Bossuyt PM, Kleijnen J. The development of QUADAS: a tool for the quality assessment of studies of diagnostic accuracy included in systematic reviews. BMC Med Res Methodol. 2003;3:25.
3. Kitchener L, Alderson P, Eisinga A, Hetherington J, Owens N. Glossary of Terms in The Cochrane Collaboration. Version 4.2.5 (updated May 2005). The Cochrane Collaboration. 2005;Available from: www.cochrane.org.
4. Richardson WS, Wilson MC, Nishikawa J, Hayward RS. The well-built clinical question: a key to evidence-based decisions. ACP J Club. 1995;123(3):A12-3.
5. Liberati A, Altman DG, Tetzlaff J, Mulrow C, G?tzsche PC, Ioannidis JP, et al. The PRISMA statement for reporting systematic reviews and meta- analyses of studies that evaluate health care interventions: explanation and elaboration. Ann Intern Med. 2009;151(4):W65-94.
Conflict of Interest:
Dr. Dewey: Research Grants: European Regional Development Fund, Joint program from the German Science Foundation (DFG) and the German Federal Ministry of Education and Research (BMBF) for meta-analyses, German Heart Foundation/German Foundation of Heart Research, GE Healthcare (Amersham), Bracco, Guerbet, and Toshiba Medical Systems. Speakers Bureau: Toshiba Medical Systems, Guerbet, Cardiac MR Academy Berlin, and Bayer-Schering. Consultant: Guerbet. Cardiac CT Courses in Berlin: www.ct-kurs.de. Book Author: "Coronary CT Angiography", Springer, 2009. "Cardiac CT", Springer 2011. Institutional master research agreements with Siemens Medical Solutions, Philips Medical Systems, and Toshiba Medical Systems. The terms of these arrangements are managed by the legal department of Charite - Universitaetsmedizin Berlin.