Week 2.2: Evidence about diagnosis Flashcards
What is an index test?
Diagnostic test of interest
What is sensitivity?
Percentage of patients with the condition that had a positive test result using the index test
How do you classify the group of participants who have the condition, but have a negative test result?
False negative
What is the positive predictive value?
Probability that the patients with a positive test truly have the disease
How do you calculate sensitivity?
True positive/true positive + false negative
How do you calculate specificity?
True negative/true negative + false positive
How do you calculate the positive predictive value?
True positive/true positive + false positive
How do you calculate the negative predictive value?
True negatives/true negative + false negative
How do you calculate positive predictive value?
True positive/true positive + false positive
What do likelihood ratios predict?
Predict the presence of diagnosis
How do you calculate the negative predictive value?
True negative/true negative + false negative
What does SnNOut mean?
High sensitivity, negative, helps rule out
What does SpPIn mean?
Specificity, positive, helps rule in
What does a positive likelihood ratio represent?
How much more likely is a positive test to be found in a with person with the condition than in a person who does not have the condition
What does a negative likelihood ratio represent?
How much more likely is a negative test to be found a person without the condition that in a person with it
What are the significant positive likelihood ratio values?
= 1: useless
>2: helps rule in disease
>10: extremely good for ruling in disease
What are the significant negative likelihood ratio values?
= 1: useless
<0.5: helps rule out disease
<0.1: extremely good for ruling out disease
How is the likelihood ratio of a positive test calculated?
sensitivity/(1 - specificity)
How is the likelihood ratio of a negative test?
(1 - sensitivity)/specificity
What is a gold standard test?
The most accurate test available, regardless of how invasive, expensive or time consuming
What does a cohort study involve? How does a cross sectional study compare?
People with a particular clinical presentation, who present at a particular hospital, undergo both the gold standard and index test, whereas in cross sectional studies, these people are recruited.
What does a case-control study population involve?
- People who clearly have the disease
- People who clearly do not have the disease
Both undergo gold standard and index test, to discriminate between extreme cases.
What is specificity?
The percentage of people that do not have the condition that were correctly identified as a negative result with the index test
