Lecture 21-23 - Screenings in Medicine Flashcards Preview

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Flashcards in Lecture 21-23 - Screenings in Medicine Deck (21)
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1

What two questions are important to ask of medical screening tests?

(L21 S4)

-how ACCURATE is the test
-how CONFIDENT can you be about the prediction of disease status from the results

2

What are the four outcomes from a screening test and what differentiates them?

(L22 S6-9)

True positive (A):
-CORRECT reporting of a POSITIVE result and patient actually HAS the disease

True negative (D):
-CORRECT reporting of NEGATIVE result and patient actually DOES NOT have disease

False positive (B):
-INCORRECT reporting of POSITIVE result and patient DOES NOT have disease

False negative (C):
-INCORRECT reporting of NEGATIVE result and patient DOES have disease

3

What two factors can be used to assess how accurate a screening test is in determining disease status?

(L21 S10)

-sensitivity
-specificity

4

How are sensitivity and specificity evaluated after they have been calculated?

(L21 S10)

-comparison to known disease status using a “gold standard”

5

What does sensitivity represent?
What does a high sensitivity indicate about a test?

(L21 S11)

-how well a test can detect disease pressence when the disease is actually present
-sensitivity = TP / (TP + FN) or A / (A + C)

-high sensitivity indicates a low false negative rate

6

What does specificity represent?
What does a high specificity indicate about a test?

(L21 S12)

-how well a test can detect disease absence when the disease is actually absent
-specificity = TN / (TN + FP) or D / (B + D)

-high specificity indicates a low false positive rate

7

What two factors can be used to assess confidence in prediction of disease presence or absence from a screening test?

(L21 S15)

-positive predictive value
-negative predictive value

8

What does positive predictive value (PPV) represent?

(L21 S16)

-how accurately a positive test predicts the presence of disease
-PPV = TP / (TP + FP)
-PPV = A / (A + B)

9

What does negative predictive value (NPV) represent?

(L21 S17)

-how accurately a negative test predicts the absence of disease
-NPV = TN / (TN + FN)
-NPV = D / (C + D)

10

Prevalence of a disease in a community is a factor in __________ and __________ but is not a factor in __________ and __________.

(L22 S18-21)

PPV; NPV; sensitivity, specificity

11

The lower the specificity, the lower the __________.

(L22 S18-21)

PPV

12

What does diagnostic accuracy/precision represent?

(L22 S22)

-proportion of screenings where a patient is correctly identified
- DA/DP = (TP + TN) / (all patients)
- DA/DP = (A + D) / (A + B + C + D)

13

What does likelihood ratio represent?

(L22 S24)

-ratio of the probability of a person with disease receiving a test result and the probability of somebody without disease getting that same result
-can be calculated for both a positive result (LR+) or a negative result (LR-)

14

What is likelihood ratio positive (LR+) and how is it calculated?

(L22 S25)

-ratio of the probabilities of a positive test in those with disease and the probability of a positive test of those without disease

-sensitivity / (1 - specificity)
-(A / (A + C)) / (B / (B + D))

15

What is likelihood ratio negative (LR-) and how is it calculated?

(L22 S26)

-ratio of the probabilities of a negative test in those with disease and the probability of a negative test of those without disease

-(1- sensitivity) / specificity
-(C / (A + C)) / (D / (B + D))

16

To be considered useful, a test should have a LR+ of __________ and a LR- of __________.

(L22 S27)

>10; <0.1

17

What is validity?

(L23 S28)

-ability to accurately identify those with disease and those without disease
-precision of results

18

Differentiate between internal validity and external validity.

(L23 S28)

Internal validity:
-how accurately a studies results reflect the true conditions of a study population

External validity:
-how accurately a studies results reflect true conditions of a population other than the one that was studied
-generalizability

19

What is reliability?

(L23 S29)

-the ability of a test to give the same results with repeated used
-degree of reproducibility or consistency

20

What relationship do validity and reliability have?

(L23 S29)

-valid tests are always reliable
-reliable tests are not always valid

21

What is a cutoff value?
What effect does changing a cut off value have on the outcomes of a test?

-the value of a test used to differentiate between presence of disease or absence of disease