Screenings in Medicine

Question 1

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?

Answer 1

prevalence must be the same in both communities in order for them to have the same PPV and NPV

Question 2

What are sensitivity and specificity values for a test based on?

Answer 2

known disease status from some type of “gold standard”

Question 3

What do sensitivity and specificity describe?

Answer 3

the accuracy of the test result

Question 4

What do PPV and NPV describe?

Answer 4

the accuracy of the “prediction of disease”

Question 5

Define the following screening-related parameter: True positive (TP)

Answer 5

a test correctly reports a positive result in a patient that actually does have the disease

Question 6

Define the following screening-related parameter: false positive (FP)

Answer 6

test incorrectly reports a positive result in a patient that actually does not have the disease

Question 7

Define the following screening-related parameter: True Negative (TN)

Answer 7

test correctly reports a negative result in a patient that actually does not have the disease

Question 8

Define the following screening-related parameter: False Negative (FN)

Answer 8

test incorrectly reports a negative result in a patient that actually does have the disease

Question 9

Define and state the equation for the following screening-related parameter: Positive Predictive Value (PPV)

Answer 9

The proportion of TP’s in pts with a positive test

Equation: PPV = TP / (TP + FP) x 100

Question 10

Define and state the equation for the following screening-related parameter: Negative Predictive Value (NPV)

Answer 10

The proportion of TN’s in pts with a negative test

Equation: NPV = TN / (TN + FN) x 100

Question 11

Define and state the equation for the following screening-related parameter: Sensitivity

Answer 11

the proportion of time that a test is positive in a pt that DOES have the disease

Equation: Sensitivity = TP / (TP + FN) x 100

Question 12

Define and state the equation for the following screening-related parameter: Specificity

Answer 12

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

Question 13

Define and state the equation for the following screening-related parameter: Diagnostic Accuracy/Precision (DA or DP)

Answer 13

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

Question 14

Define and state the equation for the following screening-related parameter: Likelihood Ratio Positive (LR+)

Answer 14

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))

Question 15

Define and state the equation for the following screening-related parameter: Likelihood Ratio Negative (LR-)

Answer 15

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))

Question 16

Define Internal Validity

Answer 16

the extent to which the results of a study, accurately represent what was being assessed

Question 17

Define External Validity

Answer 17

the extent to which the results of a study are applicable to other populations outside of the study (also called generalizability)

Question 18

Define Reliability

Answer 18

the ability of a test to give the SAME result(s) on repeated uses

Question 19

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?

Answer 19

sensitivity: would decrease

Specificity: would increase