Vascular Technology Lecture 34: Test Validation (Statistical Profile and Correlation) HHHoldorf

Hint: Numerator Denominator

Quality Assurance Statistics Sensitivity Specificity Positive Predictive value (PPV) Negative Predictive value (NPV) Accuracy

Sensitivity Definition: The ability of a test to detect disease Calculation: # of true positive tests # of all positive diagnosis detected by the gold standard

Specificity Definition: The ability of a test to identify normalcy Calculation # of true negative tests # of all negative diagnoses detected by the gold standard

Positive Predictive Value (PPV) Definition: How often positive study is correct Calculation # of true positive tests # of all positive noninvasive studies (True positive + False Positives)

Negative Predictive Value (NPV) Definition: How often negative study is correct Calculation: # of true negative tests # of all negative noninvasive studies (True negatives + false negatives)

Accuracy Definition: How good a test is Calculation: Total # of correct tests Total # of all studies NOTE: Calculation falls between sensitivity as well as between PPV and NPV

Statistical Correlations The following 2 x 2 factorial table provides a well accepted method for calculating statistics for the vascular laboratory. Chi-square: “Relating to or denoting a statistical method assessing the goodness of fit between observed values and those expected theoretically”.

A + C Accuracy = A + D Sensitivity = __A__ Specificity = D___ B + D A + B + C + D Sensitivity = __A__ A + C Specificity = D___ B + D

D Positive Predictive Value = A + B Negative Predictive Value = C + D

In an examination situation, the X – axis, and Y – axis may be changed, i.e., Gold Standard along vertical axis and noninvasive studies along horizontal axis.

In-class exercise: 140 patients had noninvasive and invasive venous studies. 68 of the noninvasive AND invasive studies showed an acute DVT and are considered true positives. 54 showed no evidence of disease (true negatives). 12 were false negative, e. g., the noninvasive study was negative but the venogram was positive. In 6 cases, the noninvasive studies were positive, but the venogram was negative (false positive).

What is the accuracy? What is the sensitivity? What is the specificity? What is the Positive predictive value? What is the negative predictive value?

Answers

Homework Text Book SDMS Assignments Chapter 24: Statistical Profile and Correlation Pages 355 – 362 SDMS Assignments