SCREENINGS Flashcards
What are 2 questions patients should ask their physician when a medical screening test is recommended?
How accurarte is the test?
How confident will you be in predection
WHat is a true positive (TP)?
Test correctely reports a postive result in a pateint that actually does have the disease
What is a true negative? (TN)
Test correctly reports a negative result in a patient that actually does not have diease
What is a false postive? (FP)
Test incorrectly reports a postive result in a patient that actually does not have the disease
What is a falase negative?
Test incorrectly reports a negative result when the patient actually does have diease
What is sensitivity and specifity?
They describes the accurarcy of test result based on known dieased status from gold standards (via comparisons)
only uses A and D values from 2x2
What is sensitivity?
How well a test can dectect presence of disease when in fact disease is present
Proportion (%) of the time that a test is positive in a patient that does have the diease
(A high sensitive test has a low false negative rate ) ;
( TP / (TP +FN) ) * 100% or ( TP/ (all dieased) ) * 100% or ( A/ (A+C) ) * 100%
What is specificity?
How well a test can detect absence of disease when infact the diesease is absent
false negativity of test in healthy
Proportion of time that a TEST is negative in a patient that does not have the disease
a high specific test has a low false positive rate
(TN/ (TN +FP) *100% or TN / (all not dieased) x 100% or D/ ( B + D) * 100
What is negative predictive value? (NPV)
HOw accurately a neative test predicts the absence of disease
Proportion of % of TN in Patients with a negative Test (correct prediction)
NPV = TN / (TN + FN) X 100%
NPV = TN / (ALL NEGATIVE TESTS) X 100
NPV = D / (C+D) X 100%
WHAT IS POSTIVE PREICTIVE VALUE (PPV)
how accurately a postive test predicts the presence of dsease
Proportion (%) of TP in patients with a postitive test (corrects prediction)
also referred to as PRedict value positive ( PVP)
PPV = = TP / (TP + FP) X 100%
PPV = TP / (ALL POSITIVE TEST ) X 100 %
PPV = A / ( A+ B) X 100
What does the postive predictive value and negative predictive value describe?
ACcuracy of prediction of disease based on known test results
What is diagnostic accuracy (DA) or Diagnostic Precison (DP)?
Proportion of % of tota screening that a patient has correctly identified as either have diease (TP) or not having the diease (TN) with either a postive or negative test, respectively
DA or DP = (TP + TN) / (TP + FP + FN + TN ) x 100%
or
= (TP + TN) / All patients x 100%
= (A + D) / (A + B + C + D)
What are likeihood Ration’s (LR)
Ratios of 2 probabilities
Ratio of the probability of % of a given test result (postive or Negative ) for a person With diease / probability % of the same test result ( postive or negative) for a person without diease
Can be calculated for both positive (+) and (-)
What is likelihood ratio postivie (LR+)
Probability (%) of a postiive test in the presence of diesease / probability of a postive test in the absence of dieaase
“what are the chances that a postive rest will result in the presence of diease compared to absense of diease”
= [A/ ( A+C)] / [B / (B + D )]
= sensitivity / ( 1 - specificity)
