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Flashcards in Epi Class 11 Deck (21):
1

Screening

the application of a test to persons without known disease for the purpose of
determining the likelihood that they have the disease.

Screening is a type of secondary prevention.

Screening tests are not diagnostic. Fundamental to screening strategies is the idea that early detection of disease will lead to more favorable outcome

2

When is screening not appropriate

When there is no effective treatment for the disease

3

Screening criteria

1. The disease should be of public health importance.
- Disease should be SEVERE.
- Disease should have a high FREQUENCY in the population.

2. There should be an acceptable TREATMENT for individuals with the disease.

3. Facilities for diagnosis and treatment should be AVAILABLE to the screened population.

4. There should be a recognizable LATENT (early asymptomatic) stage of the disease. (Implies that the natural history of the disease is understood.)

5. The screening test should be ACCEPTABLE to the population (in terms of cost, risk, comfort, and the information provided).

6. The screening test should be VALID.

4

Validity

How closely does this test allow us to observe the actual presence or absence of disease?

Does the test really measure what we intend to measure?

Are the classifications of disease status accurate?

5

Sensitivity

Ability to detect disease in the diseased

The probability that a person with the disease will be classified as having the disease.

A screening test with 90% sensitivity will correctly identify 90% of persons with disease as diseased. The other 10% will be incorrectly identified as non-diseased.

6

Sensitivity formula

TP / TP + FN

or

A / A + C

7

TP

Ture Positive

8

FP

False Positive

9

TN

True Negative

10

FN

False Negative

11

Specificity

ability to detect non-disease in the non-diseased

The probability that a person without the disease will be classified as non-diseased.

A screening test with 95% specificity will correctly identify 95% of persons without
disease as disease-free. The other 5% will be incorrectly identified as diseased

12

Specificity formula

TN / TN + FP

or

D / B + D

13

Validity table

*look up in notes*

14

Positive Predictive Value (PPV OR PV+)

the proportion of the people who test
positive who actually have the disease

15

Negative Predictive Value (NPV OR PV–)

the proportion of the people who test
negative who actually do not have the disease

16

PV+ formula

TP / TP + FP

or

A / A + B

17

PV- formula

TN / TN + FN

or

D / C + D

18

Kappa

a measure of the degree of nonrandom agreement between observers or measurements of some categorical variable

How much do two people agree on the result when it isn't a common sense answer

19

Interpreting Kappa

Kappa ranges from 1 to -1

If the measurements agree more often than expected by chance, kappa is positive.
- If the agreement (concordance) is
complete, kappa = 1

If there is no more or less than chance agreement, kappa = 0.

If the measurements disagree more than expected by chance, kappa is negative.
- If the disagreement (discordance) is
complete, kappa = -1

20

If the sensitivity of the test increases...

The specificity of the test decreases

21

If the specificity of the test increases...

The sensitivity of the test decreases