Screenings in Medicine Flashcards
what factor must be the same for 2 different communities, using the same diagnostic tests, so that the PPV and NPV values are the same?
prevalence must be the same in both communities in order for them to have the same PPV and NPV
What are sensitivity and specificity values for a test based on?
known disease status from some type of “gold standard”
What do sensitivity and specificity describe?
the accuracy of the test result
What do PPV and NPV describe?
the accuracy of the “prediction of disease”
Define the following screening-related parameter: True positive (TP)
a test correctly reports a positive result in a patient that actually does have the disease
Define the following screening-related parameter: false positive (FP)
test incorrectly reports a positive result in a patient that actually does not have the disease
Define the following screening-related parameter: True Negative (TN)
test correctly reports a negative result in a patient that actually does not have the disease
Define the following screening-related parameter: False Negative (FN)
test incorrectly reports a negative result in a patient that actually does have the disease
Define and state the equation for the following screening-related parameter: Positive Predictive Value (PPV)
The proportion of TP’s in pts with a positive test
Equation: PPV = TP / (TP + FP) x 100
Define and state the equation for the following screening-related parameter: Negative Predictive Value (NPV)
The proportion of TN’s in pts with a negative test
Equation: NPV = TN / (TN + FN) x 100
Define and state the equation for the following screening-related parameter: Sensitivity
the proportion of time that a test is positive in a pt that DOES have the disease
Equation: Sensitivity = TP / (TP + FN) x 100
Define and state the equation for the following screening-related parameter: Specificity
the proportion of time that a test is negative in a pt that DOES NOT have the disease
Equation: Specificity = TN / (TN + FP) x 100
Define and state the equation for the following screening-related parameter: Diagnostic Accuracy/Precision (DA or DP)
the proportion of total screenings that a pt is correctly identified as either a TP or TN, with either a positive or negative test result respectively
Equation: DA or DP = (TP + TN) / (everyone in the study) x 100
Define and state the equation for the following screening-related parameter: Likelihood Ratio Positive (LR+)
The probability of a positive test in the presence of disease divided by the probability of a positive test in the absence of disease
(The ratio for True positives in the diseased over the ratio of the false positives in the non-diseased.)
Eq: (A / (A+C)) / (B / (B+D))
Define and state the equation for the following screening-related parameter: Likelihood Ratio Negative (LR-)
The probability of a negative test in the presence of disease divided by the probability of a negative test in the absence of disease
(The ratio for false negatives in the diseased over the ratio for the true negatives in the non-diseased)
Eq: (C / (A+C)) / (D / (B+D))
Define Internal Validity
the extent to which the results of a study, accurately represent what was being assessed
Define External Validity
the extent to which the results of a study are applicable to other populations outside of the study (also called generalizability)
Define Reliability
the ability of a test to give the SAME result(s) on repeated uses
In a study that has a sensitivity of 90% and a specificity of 90% and a cut off value of 60, what would happen (words not numbers) to the sensitivity and specificity if the cut off value is moved to 70?
sensitivity: would decrease
Specificity: would increase
