Screenings in Medicine Flashcards
What are the 2 questions that patients should ask their physician when a medical screening is recommended?
- How accurate is the screening test?
- How confident will you be in your prediction?
True Positive (TP)
Test correctly reports positive result in a patient that actually does have the disease
True Negative (TN)
Test correctly reports a positive result in a patient that actually does not have the disease
False Positive (FP)
Test incorrectly reports a positive result in a patient that actually does not have the disease
False Negative (FP)
Test incorrectly reports negative result in a patient that actually does have the disease
Sensitivity Definition
How well a test can detect presence of disease when the disease is present
Sensitivity Equation
Sensitivity = TP / (TP + FN) x 100
= TP / all diseased x 100
Specificity Definition
How well a test can detect absence of disease when the disease is absent
Specificity Equation
Specificity = TN/ (TN + FP) x 100
= TN / all not diseased x 100
Positive Predictive Value Definition
How accurately a positive test predicts the presence of disease
Positive Predictive Value (PPV) Equation
PPV = TP/ (TP + FP) x 100
= TP / all positive tests x 100
Negative Predictive Value (NPV) Definition
How accurately a negative test predicts the absence of disease
NPV Equation
NPV = TN / (TN + FN) x 100
= TN / all negative tests x 100
Diagnostic Accuracy (DA) or Diagnostic Precision (DP) Definition
Proportion of time that a patient is correctly identifies as either having a disease or not having a disease with a positive or negative test, respectively
DA or DP Equation
DA/DP = (TP + TN) / ( TP + FP + FN + TN) x 100
= (TP + TN) / All patients X 100
Likelihood Ratio Positive
Probability of positive test with disease / probability of positive test without disease
- [A/A+C] / [B/B+D]
Likelihood Ratio Negative
Probability of negative test with disease / probability of negative test without disease
[C/A+C] / [D/B+D]
Validity
Ability to accurate discern between those that do and those that do not have disease
Internal Validity
Extent to which results accurately reflect what was being assessed
External Validity
Extent to which results are applicable to other populations (Generalizability)
Reliability
Ability of a test to give the same result on repeated uses
What should LR+ be to demonstrate the test is most beneficial?
> 10
What should LR- be to demonstrate the test is most beneficial?
<0.1
