Diagnosis and Therapy Cases Aortic Aneurysm Diagnosis Case - Aortic Aneurysm Step 3: Assess evidence Are the results likely to be valid? Criteria 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? If yes, explain. Are the results of the study important? Are the likelihood ratios for the test results presented or data necessary for their calculation provided? If the article gives the numbers of patients with and without the disease, you can tabulate the information in the following 2x2 table. This is a common method of keeping track of the results of studies, and will allow you to make further calculations listed below. Some articles will directly give the answers to the calculations saving you a step. In this example, the results of the sensitivity, specificity and likelihood ratios are given directly in the paper. It is therefore not necessary to complete these calculations by hand. In this case, many different likelihood ratios are given, and we used ALL EXAMINATIONS from the table to complete this part of the article assessment. 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 Calculate the Sensitivity a/(a+c): Calculate the Specificity d/(b+d): Calculate the Positive predictive value a/(a+b): Calculate the Negative predictive value d/(c+d): Calculate the Likelihood ratio positive [a/(a+c)]/[b/(b+d)]: Calculate the Likelihood ratio negative [c/(a+c)]/[d/(b+d)]: Any concerns about the importance of the evidence? If yes, explain. Continue to Step 4: Apply the evidence