Epi - L6 - Screenings in Medicine

Question 1

what two questions should patients ask their physician when a medical screening test is recommended?

Answer 1

1. how ACCURATE is the screening test you are about to recommend for me? (specificity and sensitivity test)
2. when the test result are announced, how CONFIDENT will you be in your prediction of whether i do or don’t have the disease?

Question 2

what are the 4 possible outcomes of the screening?

Answer 2

1. true-positive
2. false- neg
3. false-pos
4. true-neg

Question 3

Elements of screenings in medicine: when checking for accuracy of a test, what are you looking for?

Answer 3

1. sensitivity
2. specificity

this describes accuracy of TEST RESULTS (based on known disease status from “gold” standard)

Question 4

Sensitivity

Answer 4

• looking at the accuracy of the TEST

how well a test can DETECT PRESENCE OF DISEASE hone in fact the disease is PRESENT (positivity-of-test in the diseased)

• its a percentage; Box A
• proportion (%) of time that a TEST is POSITIVE in a patient that DOES have the disease
• • a highly sensitive test has a low false negative rate

Sensitivity = TP/ (TP + FN)*100%
Sensitivity = TP/ (all diseased)*100%

Question 5

Specificity

Answer 5

• how well a TEST can DETECT ABSENCE OF DISEASE when in fact the disease is ABSENT (negativity-of-test in the Healthy)
• Proportion (%) of time that a TEST is NEGATIVE in a patient that DOES NOT have the disease ( a highly specific tests has a low false positive rate)

Spec. = TN/ (TN+FP)*100%
Spec. = TN/(all NOT diseased)*100%

Question 6

elements of screenings in Medicine: confidence;

Answer 6

when the test results are announced, how CONFIDENT will you be in your prediction of whether I do or don’t have a disease?

-Positive predictive value
- negative predictive value
=describes accuracy of PREDICTION OF DISEASE (based on known test results)

Question 7

positive predictive value

Answer 7

• how accurately a POSITIVE test PREDICTS the presence of a disease
• proportion of TP;’s in patient with a positive test (correct prediction)

PPV = TP/(TP+FP)*100%
PPV = TP / (all positive tests)*100%

Question 8

negative predictive value

Answer 8

• how accurately a negative test predicts the absence of a disease
• proportion of TN’s in patients with a negative test (correct prediction)

NPV = TN / (TN + FN)*100%
NPV = TN / (all neg tests) * 100%