Epi Class 11

Question 1

Screening

Answer 1

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

Question 2

When is screening not appropriate

Answer 2

When there is no effective treatment for the disease

Question 3

Screening criteria

Answer 3

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.

Question 4

Validity

Answer 4

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?

Question 5

Sensitivity

Answer 5

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.

Question 6

Sensitivity formula

Answer 6

TP / TP + FN

or

A / A + C

Question 7

TP

Answer 7

Ture Positive

Question 8

FP

Answer 8

False Positive

Question 9

TN

Answer 9

True Negative

Question 10

FN

Answer 10

False Negative

Question 11

Specificity

Answer 11

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

Question 12

Specificity formula

Answer 12

TN / TN + FP

or

D / B + D

Question 13

Validity table

Answer 13

look up in notes

Question 14

Positive Predictive Value (PPV OR PV+)

Answer 14

the proportion of the people who test

positive who actually have the disease

Question 15

Negative Predictive Value (NPV OR PV–)

Answer 15

the proportion of the people who test

negative who actually do not have the disease

Question 16

PV+ formula

Answer 16

TP / TP + FP

or

A / A + B

Question 17

PV- formula

Answer 17

TN / TN + FN

or

D / C + D

Question 18

Kappa

Answer 18

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

Question 19

Interpreting Kappa

Answer 19

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

Question 20

If the sensitivity of the test increases…

Answer 20

The specificity of the test decreases

Question 21

If the specificity of the test increases…

Answer 21

The sensitivity of the test decreases