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- 1. Evidence Based Diagnosis
- 2. When a Patient Has a Problem <ul><li>The doctor reaches a diagnosis by: </li></ul><ul><ul><ul><ul><ul><li>Clinical data </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Diagnostic tools </li></ul></ul></ul></ul></ul>
- 3. Increasing use of Diagnostic tests: - Availability. - The urge to make use of new technology.
- 4. The evaluation of diagnostic techniques is less advanced than that of treatments ( NO phase I, II, III, IV). New Diagnostic tests
- 5. Relevance <ul><li>First, the test should be one that is feasible for you in your community </li></ul><ul><li>Example: brain biopsy is an accurate test for diagnosing dementia, it’s not practical for my (living) patients! </li></ul><ul><li>Can I apply the test to my patients? (Availability, Cost) e.g MRI </li></ul>
- 6. Validity <ul><li>The degree to which the results of a study are likely to be true and free from bias. </li></ul><ul><li>It should be compared to a gold reference standard </li></ul>
- 7. Caution <ul><li>reference standard used should be acceptable (e.g HSG vs DL) </li></ul><ul><li>Both reference standard and test should be applied to all patients </li></ul>
- 8. Independent <ul><li>the decision to perform the reference standard should ideally be independent of the results of the test being studied. </li></ul>
- 9. Ask yourself <ul><li>the patient sample should include an appropriate spectrum of patients to whom the diagnostic test will be applied in clinical practice </li></ul>
- 10. Rule of Thumb <ul><li>at least 100 participants to ensure an appropriate "spectrum" of disease </li></ul>
- 11. 2 x 2 table comparing the results of a diagnostic test with a reference standard reference standard disease no disease test abnormal true pos. [a] false pos. [b] test normal false neg. [c] true neg. [d]
- 12. sensitivity <ul><li>probability of a positive test among patients with disease </li></ul><ul><li>i.e Ability to diagnose </li></ul>
- 13. specificity <ul><li>probability of a negative test among patients without disease </li></ul><ul><li>i.e Ability to exclude </li></ul>
- 14. 2 X 2 Table b (false positive) a (true positive) d (true negative) c (false negative)
- 16. Keep in Mind <ul><li>sensitivity and specificity by themselves are only useful when either is very high (over typically, 95% or higher). </li></ul>
- 17. Who wants what ? main interest Methodologist sensitivity specificity Doctor accuracy Patient Probability
- 18. Likelihood Ratio <ul><li>The "positive likelihood ratio" (LR+) tells us how much to increase the probability of disease if the test is positive </li></ul><ul><li>The "negative likelihood ratio" (LR-) tells us how much to decrease it if the test is negative </li></ul>
- 19. Likelihood Ratio <ul><li>LR+= </li></ul><ul><li>probability of a +ve test in those who have the disease___ probability of a +ve test in those who do not have the disease </li></ul><ul><li>= sensitivity 1-specificity </li></ul><ul><li>LR-= </li></ul><ul><li>probability of a -ve test in those who have the disease___ probability of a -ve test in those who do not have the disease </li></ul><ul><li>= 1-sensitivity specificity </li></ul>
- 20. Interpretation LR Large and often conclusive increase in the likelihood of disease > 10 Moderate increase in the likelihood of disease 5 - 10 Small increase in the likelihood of disease 2 - 5 Minimal increase in the likelihood of disease 1 - 2 No change in the likelihood of disease 1 Minimal decrease in the likelihood of disease 0.5 - 1.0 Small decrease in the likelihood of disease 0.2 - 0.5 Moderate decrease in the likelihood of disease 0.1 - 0.2 Large and often conclusive decrease in the likelihood of disease < 0.1
- 22. Why LR <ul><li>The LR+ corresponds to the clinical concept of "ruling-in disease" </li></ul><ul><li>The LR- corresponds to the clinical concept of "ruling-out disease“ </li></ul>
- 23. Patient oriented !!!!!!! <ul><li>Your 45 year old patient has a mammogram. The study is interpreted as "suspicious for malignancy" by your radiologist. </li></ul><ul><li>Your patient asks you: "Does this mean I have cancer?", and you (correctly) answer "No, we have to do further testing." </li></ul>
- 24. <ul><li>Your patient then asks, "OK, I understand that the mammogram isn't the final answer, but given what we know now, what are the chances that I have breast cancer?". </li></ul>
- 25. Is it Easy!!! <ul><li>Assume that the overall risk of breast cancer in any 45 year old woman, regardless of mammogram result, is 1%. Assume also that mammography is 90% sensitive and 95% specific. Then, select your answer below: 1% 15% 60% 85% 95% </li></ul>
- 26. If you know that the risk of breast cancer in any 45 year old woman is 1% and that mammography is 90% sensitive and 95% specific. What do you think your patient’s probability of having breast cancer is? LR+=Sens/100-Spec =90/5=18
- 27. Disease ruled IN Disease ruled OUT Disease not ruled in or out Determined by: Complications of untreated disease Risks of therapy Complications of tests Cost Above this point, treat Below this point, no further testing
- 28. ROC curve is simply a graph of sensitivity vs (1-specificity)
- 29. specificity specificity sensitivity sensitivity BW Mol: Meta-analysis of diagnostic test studies. TFO 8; 60-65, 2004 Serum progesterone in diagnosing ectopic pregnancy.
- 30. Score Systematic Collaboration of Ovarian Reserve Evaluation <ul><li>systematic reviews of Diagnostic tests </li></ul>
- 31. <ul><li>THANK YOU </li></ul>

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