Answering Clinical Questions of Diagnosis A worksheet for evidence-based medicine Step 1: Define a clinical question PICO (Patient or Problem; Intervention; Comparison Intervention; Outcome) Your question: Step 2: Find evidence Use the terms from your PICO question to search a current literature database. When using PubMed, the easiest approach is to insert the most important words from your question with AND between each one. Search Terms Used: Citation: Step 3: Assess Evidence Brief Summary of the Methods: Are the results likely to be valid? Question Yes No Was there an independent, blind comparison with a reference ("gold") standard of diagnosis? Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom we would use it in practice)? Was the reference standard applied regardless of the diagnostic test result? Was the test validated in a second, independent group of patients? Any validity concerns? Yes No If yes, explain. Are the results of the study important? Question Yes No Are the likelihood ratios for the test results presented or data necessary for their calculation provided? Disease/Disorder used for the calculations below: Diagnostic test used for the calculations below: Reference standard used for the calculations below: Disease Present Disease Absent Diagnostic test positive a b Diagnostic test negative c d Sensitivity=a/(a+c) Specificity=d/(b+d) Positive predictive value=a/(a+b) Negative predictive value=d/(c+d) LR(+)=[a/(a+c)]/[b/(b+d)]=sensitivity/(1-specificity) LR(-)=[c/(a+c)/[d/(b+d)]=(1-sensitivity)/specificity Any concerns about the importance of the evidence? Yes No If yes, explain. Step 4: Apply the evidence to your patient Questions: Is the diagnostic test available, affordable, accurate, and precise in your setting? Estimate your patient's pre-test probability (%) How is your patient similar to the study population? How is your patient different? Will these differences affect the applicability of the test to your patient? Determine your patient's post-test probability for a positive result (%) What will you do with a positive result? Determine your patient's post-test probability for a negative result (%) What will you do with a negative result? Will the results help your patient? Why or why not? Press CTRL-P to print this worksheet. Adapted from: Sacket DL et al. Evidence-based Medicine: How to practice and teach EBM. 3rd Edition. Churchill Livingstone. 2000.