Ch 7b Sensitivity + Specificity Flashcards
What is FNV?
-False negative value
-The # of diseased persons testing negative
What is FPV?
-False positive value
-The # of non-diseased persons who tested positive
What is TD?
Total # of diseased persons
What is TN?
Total # of persons testing negative
What is TND?
Total # of non-diseased persons
What is TNV?
-True negative value
-The # of disease free persons testing negative
What is TOT?
Total # of persons in the study
What is TP?
Total # of persons testing positive
What is TPV?
-True positive value
-The # of diseased persons testing positive
Is the sensitivity for scrotal + OB exams high or low?
High - b/c u/s is the gold standard
If the test result is positive: list the correct definitions for the disease, non-diseased + total?
Disease: TPV (true positive value)
Non-diseased: FPV (false positive value)
Total: TP (total positive people)
If the test result is negative: list the correct definitions for the disease, non-diseased + total?
Disease: FNV (false negative value)
Non-diseased: TNV (true negative value)
Total: TN (total negative people)
List the total test results: list the correct definitions for the disease, non-diseased + total?
Disease: TD (total diseased people)
Non-diseased: TND (total non-diseased people)
Total: TOT (total people in study)
List the sensitivity formula?
SENS = TPV/TD
Define sensitivity?
-True positive rate
-The sensitivity of a test is the proportion of people with the disease who will have a positive result
A highly sensitive test is one that correctly identifies what?
Patients with a disease
A test that is 100% sensitive will identify what?
All patients who have the disease
List the specificity formula?
SPEC = TNV/TND
Define specificity?
-True negative rate
-The specificity of a test is the proportion of people without the disease who will have a negative result
The specificity of a test refers to how well a test identifies what?
Pt’s who do not have a disease
A test that has 100% specificity will identify what?
100% of pt’s who do not have the disease
Do high sensitivity tests have high or low specificity?
Low
(think they are inverse of each other)
High sensitivity + low specificity is good for catching actual cases of the disease. Do they have a high or low rate of false positives?
High false positive rate
(going to call pt’s back for more testing than they need to. A biopsy should be done)
Give an example of a test that generally has a high sensitivity (70-80%) + low specificity?
Mammograms
(sensitivity depends on tumor size, pt age, etc)
High specificity + low sensitivity has a high or low rate of false negatives?
Higher false negative rate (misses true positives)
(bad at telling us if a person has the disease, must do other tests to check)
Give an example of a test that has low sensitivity (27%) + high specificity (94%)?
Nitrate dipstick test - used to test for urinary tract infections (UTIs) in hospitalized pt’s
List the positive predictive value formula?
PPV = TPV/TP
What is the PPV?
-Positive predictive value
-Is the probability that a positive result in a hypothesis test means that there is a real effect
-Is the probability of pt’s who have a positive test result to actually have the disease
Positive predictive values are influenced by what?
How common the disease is in the population being tested
(ex. if the disease is very common than a person with a positive test result is more likely to actually have the disease, opposed to a person with a positive test result in a population where the disease is rare)
List the negative predictive value formula?
NPV = TNV/TN
What is the NPV?
-Negative predictive value
-The probability that people who get a negative test result truly do not have the disease
-The probability that a negative test result is accurate
Give an example of a test that we would want to have a high negative predictive value?
Covid tests - we want a high NPV so we know for sure we do not have covid + do not isolate for no reason
List the accuracy of a test formula?
ACC = (TPV + TNV)/TOT
What is ACC?
-Accuracy of a test
-Is the proportion of all tests in the study (TOT) that have the correct result
