How to review a diagnostic study - PowerPoint PPT Presentation

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How to review a diagnostic study

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  1. How to review a diagnostic study CCBS Study Afternoon 12 August 2008 francesca.chappell@ed.ac.uk

  2. What is a diagnostic study? • Accuracy of an index test compared to reference standard • Accuracy very often given as sensitivity and specificity TP + FN = no. of disease +ve patients FP + TN = no. of disease -ve patients Sensitivity = TP/No. of disease +ve patients Specificity = TN/No. of disease –ve patients

  3. Factors affecting sensitivity and specificity patients intrinsic performance of test sensitivity and specificity Bias due to methods of conducting tests Bias due to (de)selection of patients Bias due to misanalysis of data

  4. How patient selection goes wrong Recruitment stage patients selected because they do or do not have the disease Patients included in the analysis patients selected for convenience Ideal patients = people who would get the test in real life to establish diagnosis Patients included in reference standard testing depending on result of index test, i.e. Verification bias Testing stage

  5. How testing goes wrong

  6. How the analysis goes wrong (1) Reference standard results Reference standard results Index test results Index test results

  7. How analysis goes wrong (2) The methods for dealing with these are complicated.

  8. Another problem • “However, evaluations were hampered because many reports lacked information on key elements of design, conduct and analysis of diagnostic studies.” Bossuyt et al. The STARD Statement http://www.stard-statement.org/

  9. Practicalities of reviewing (1) Abstract inclusion/exclusion criteria Full-text inclusion/exclusion criteria

  10. Practicalities of reviewing (2) QUADAS checklist for diagnostic studies Data extraction QUADAS: See Whiting P et al. BMC Med Res Methodol 2003;3:25 http://www.biomedcentral.com/1471-2288/3/25

  11. Document everything

  12. Meta-analysis Aim: to summarise the two-dimensionaldata

  13. FREE SOFTWARE! http://www2.napier.ac.uk/depts/fhls/diagmeta/

  14. Example 1

  15. Example 2

  16. References Loong T-W. Understanding sensitivity and specificity with the right side of the brain. BMJ 2003;327:716-719. STARD Statement http://www.stard-statement.org/ QUADAS checklist Whiting P et al. BMC Med Res Methodol 2003;3:25 (Also available in NCC HTA monograph) The Magnificent ROC http://www.anaesthetist.com/mnm/stats/roc/Findex.htm Summary ROC curves http://srdta.cochrane.org/Files/Website/Presentations/ 4_AdvancedAnalysis_SaoPaulo.pdf DiagMeta website http://www2.napier.ac.uk/depts/fhls/diagmeta/ francesca.chappell@ed.ac.uk