11: Screening for Disease

Question 1

Screening

Answer 1

The presumptive identification of unrecognized disease or defects by the application of tests, examinations, or other procedures that can be applied rapidly. Positive screening results are followed by diagnostic tests to confirm actual disease.

Question 2

Multiphasic Screening

Answer 2

Use of two or more screening tests together among large groups of people. Information obtained on risk factor status, history of illness, and health measurements. Commonly used by employers and health maintenance organizations.

Question 3

Mass Screening

Answer 3

screening on a large scale of total population groups regardless of risk status

Question 4

Selective Screening

Answer 4

Screens subsets of the population at high risk for disease.

Question 5

Mass Health Examinations

Answer 5

• Population or Epidemiologic Surveys
• Epidemiologic Surveillance
• Case Finding (Opportunistic Screening)

Question 6

Population or Epidemiologic Surveys

Answer 6

Purpose is to gain knowledge regarding the distribution and determinants of diseases in selected populations. No benefit to the participant is implied.

Question 7

Epidemiologic Surveillance

Answer 7

Aims at the protection of community health through case detection and intervention.

Question 8

Case Finding (Opportunistic Screening)

Answer 8

The utilization of screening tests for detection of conditions unrelated to the patient’s chief complaint.

Question 9

Appropriate Social Situations for Screening Tests and Programs

Answer 9

• Health problem should be important for individual and community
• Diagnostic follow-up and intervention available.
• Favorable cost-benefit ratio.
• High public acceptance.

Question 10

Appropriate Scientific Situations for Screening Tests and Programs

Answer 10

Early detection efforts are most likely successful when:

• natural history of condition is understood
• high prevalence of disease or condition

Question 11

Appropriate Ethical Situations for Screening Tests and Programs

Answer 11

It is ideal if the screening program is implement so that:

• it can alter natural history in significant proportion of those screened.
• suitable, acceptable tests for screening and diagnosis, as well as acceptable, effective methods of prevention are available.

Question 12

Characteristics of a Good Screening Test

Answer 12

• Simple
• Rapid
• Inexpensive
• Safe
• Acceptable

Question 13

Reliability

Answer 13

PRECISION. The ability of a measuring instrument to give consistent results on repeated trials.

Question 14

Repeated Measurement Reliability

Answer 14

The degree of consistency among repeated measurements of the same individual on more than one occasion.

Question 15

Internal Consistency Reliability

Answer 15

Evaluates the degree of agreement or homogeneity within a questionnaire measure of an attitude, personal characteristic, or psychologic attribute. Ex. Questionnaires with many “similar” questions.

Question 16

Interjudge Reliability

Answer 16

Reliability assessments derived from agreement among trained experts. % of agreement among judges.

Question 17

Validity

Answer 17

ACCURACY. The ability of a measuring instrument to give a true measure. Can be evaluate only if an accepted and independent method for confirming the test measurement exists.

Question 18

Content Validity

Answer 18

Degree to which a measure covers the range of meanings included within the concept.

Question 19

Criterion-Referenced Validity

Answer 19

Found by correlating a measure with an external criterion of the entity being assessed. Predictive vs. Concurrent.

Question 20

Predictive Validity

Answer 20

Denotes the ability of a measure to predict some attribute or characteristic in the future. EX. blood pressure reading and heart disease. Measure correlations of readings to future incidence.

Question 21

Concurrent Validity

Answer 21

Obtained by correlating a measure with an alternative measure of the same phenomenon taken at the same point in time. EX. Self administered depression evaluation compared to psychiatric diagnosis.

Question 22

Construct Validity

Answer 22

Degree to which the measurement agrees with the theoretical concept being investigated. (new test development)

Question 23

Reliability vs. Validity

Answer 23

• Possible to be reliable but invalid

- Impossible to be valid but unreliable

Question 24

Sources of Unreliability and Invalidity

Answer 24

• Measurement Bias
• Halo Effect
• Social Desirability Effects

Question 25

Measurement Bias

Answer 25

Constant errors that are introduced by a faulty measuring device and tend to reduce reliability of measurements.

Question 26

Halo Effect

Answer 26

Bias that affects the validity of questionnaire measurements (preconceived ideas will alter recorded data)

Question 27

Social Desirability Effects

Answer 27

Respondent answers questions in a manner that agrees with desirable social norms.

Question 28

Sensitivity

Answer 28

Ability of test to identify correctly all screened individuals who actually have the disease. A/A+C

Question 29

Specificity

Answer 29

Ability of test to identify only non-diseased individuals who actually do not have the disease. D/B+D

Question 30

Predictive Value (+)

Answer 30

Proportion of individuals screened positive by the test who actually have the disease. A/A+B

Question 31

Predictive Value (-)

Answer 31

Proportion of individuals screened negative by the test who do not have the disease. D/C+D

Question 32

Accuracy of Screening Test

Answer 32

(A+D)/(A+B+C+D)

Question 33

Prevalence

Answer 33

(A+C)/(A+B+C+D)

Question 34

Disease Prevalence vs. Predictive Value

Answer 34

• ^ Prevalence, ^ PP+, v PP-

- v Prevalence, v PP+, ^ PP-

Question 35

To improve Sensitivity:

Answer 35

Cut point used to classify individuals as diseased should be moved farther in the range of the non-diseased. Include more values.

Question 36

To improve Specificity:

Answer 36

Cut point should be moved farther in the range typically associated with the disease. Exclude more values.

Question 37

Procedures to Improve Sensitivity and Specificity

Answer 37

• Retrain Screeners: reduces misclassification in tests that require human assessment
• Recalibrate Screening Instrument: reduces imprecision
• Utilize Different Test: replace low reliability and validity with improved test
• Utilize More Than One Test: multiple readings

Question 38

Evaluation of Screening Programs

Answer 38

Potentially identify BIAS

• Randomized Control Trials
• Ecologic Time Trend Studies
• Case-Control Studies

Question 39

Sources of Bias in Screening

Answer 39

• Lead Time Bias
• Length Bias
• Selection Bias

Question 40

Lead Time Bias

Answer 40

Perception that screen-detected case has longer survival because disease was identified early.

Question 41

Length Bias

Answer 41

Particularly relevant to cancer screening. Tumors identified by screening are slower growing and have better prognosis.

Question 42

Selection Bias

Answer 42

Motivated participants have a different probability of disease than do those who refuse to participate.

Question 43

Issues in Classification of Morbidity and Mortality

Answer 43

Nomenclature and Classification of disease are central to the reliable measurement of the outcome variable in epidemiologic research.

Question 44

Nomenclature

Answer 44

Highly specific set of terms for describing and recording clinical or pathologic diagnoses to classify ill persons into groups.

Question 45

Classification

Answer 45

Statistical compilation of groups of cases of disease by arranging disease entities into categories that share similar features. Causal vs. Manifestational