Exam #1: Appraising Diagnostic Studies Flashcards
Review the steps in EBM.
1) Ask answerable questions
2) Search for evidence
3) Critical appraisal of evidence
4) Integration of evidence with expertise and patient values + application
5) Evaluate results
What are diagnostic tests used for?
- Screening a population
- Diagnosis in an individual
- Patient follow-up and management
What are the disadvantages of diagnostic testing?
- May be expensive
- Can risk morbidity or mortality
- May cause discomfort
*****False positives can cause psychological distress and lead to risk from unnecessary therapy
Are studies of diagnosis random?
NO
How are diagnostic studies designed?
1) Subject population to test
2) See what happens
3) Compare to reference standard
What are the questions you need to ask when appraising a diagnostic study?
1) What are the results?
2) Is the study valid?
3) Are the results in the study important?
4) Will the results help my patients?
What are the questions you need to ask to determine if the study is valid?
1) Is the research question clearly defined?
2) Presence or absence of disorder confirmed by “gold standard?”
3) Was the test evaluated on an appropriate spectrum of patients?
4) Reference standard applied to all patients?
*****Also need to know how the investigators knew the disorder was present AND that the comparison was blinded.
How should you determine the clinical importance of a diagnostic test?
Determine the sensitivity and specificity of the test
*****An ideal test will produce only true positives and true negatives
What is sensitivity?
How well a test finds true positives
What is specificity?
How well a test finds true negatives
What is a likelihood ratio?
Likelihood of a result in a patient with a disease vs. a patient without
What is the equation for sensitivity?
TP/ TP + FN
What is the equation for specificity?
TN/ TN + FP
Match the terms: sensitivity/ specificity and rule-in vs. rule out.
Sensitivity= Rule OUT
- SnNout
Specificity= Rule IN
- SpPin
What is pre-test probability?
An estimate of prevalence
What is post-test probability?
Probability of disease after diagnostic test
*****Note that a diagnostic test should increase this number
What does a likelihood ratio of 1 mean?
Pre and post-test probability are the same
*****This test is USELESS–it has not told you anything
What is a likelihood ratio greater than one mean?
Probability of finding the disease by test is increased
What is a likelihood ratio less than one mean?
Probability of finding the disease by test is decreased i.e. the test does NOT help you
Generally, what does Bayes Theorem state?
Likelihood of a patient having a disease is equal to the prevalence of the disease in the population
How can you determine if you should implement a test into practice?
Ask:
- Will the test be satisfactory in my setting?
- Are the results applicable?
- Will the results change my management?*
- Will patients be better off as a result of the test?
