Types of prevention, Screening, 2X2 Table

Question 1

Promotion of health at both individual and community levels by facilitating health – enhancing behaviors , preventing the onset of risk behaviors , and diminishing exposure to environmental hazards. What type of prevention?

Answer 1

Primary prevention.

• Primary prevention efforts decrease disease INCIDENCE.
• An example would be the “Hearty Heart” nutrition program for elementary school children.

Question 2

Screening for risk factors and early detection of asymptomatic or mild disease, permitting timely and effective intervention and curative treatment.
What type of prevention?

Answer 2

Secondary prevention.

• Secondary prevention efforts decrease disease PREVALENCE.
• Example :
  Community blood pressure screening.
  Physician support to quit smoking cigarettes.

Question 3

Reduction of long-term impairments and disabilities and prevention of repeated episodes of clinical illness. What type of prevention?

Answer 3

Tertiary prevention.

• The goals of tertiary prevention are to prevent recurrence and to slow progression.
• Example :
  Graded aerobic physical activity program prescribed to patients during recovery from first myocardial infarction.

Question 4

The application of a disease-detection test to people who are as yet asymptomatic is called?

Answer 4

Screening.

• Screening procedure itself does NOT formally diagnose illness.

Question 5

Two reasons why screening is important?

Answer 5

1) Diagnostic and therapeutic advances are often slow, but screening may be a “direct solution” to modify history of a disease in a population.
2) It provides a model for studying disease mechanisms and the natural history of a disease.

Question 6

Diseases for which screening has been recommended?

Answer 6

Cervical cancer
 Breast cancer
 Prostate cancer
 Colon cancer
 Diabetes
 Hypertension

Question 7

Total pre-clinical phase (TPCP)?

Answer 7

• Age 30 (Exposure neoplasia) to 55 (symptom diagnosis)

- TPCP: Begins at the initiation of disease; ends when the disease is clinically manifested (25 years in this example)

Question 8

Detectable pre-clinical phase (DPCP)

Answer 8

• Age 45 (cell exfoliate) to 55 (symptom diagnosis)

- DPCP: Begins when screening test is able to detect disease; Ends when disease is clinically evident (10 years)

Question 9

sensitivity

Answer 9

The screening test will actually classify a diseased person as likely to have the condition
A/(A+C)

Question 10

specificity

Answer 10

The screening test will actually classify a non-diseased person as unlikely to have the condition.
D/(B+D)

Question 11

Predictive Value Positive (PV+) and Predictive Value Negative (PV-)

Answer 11

• People with positive screening test results will also test positive on the diagnostic test.
  a/(a+b)
• People with negative screening test results are actually free of disease.
  d/(c+d)

Question 12

Factors that influence PV+ and PV- ?

Answer 12

1. The more specific the test, the higher the PV-
2. The higher the prevalence of preclinical disease in the screened population, the higher the PV+
3. The more sensitive the test, the higher the PV+

Question 13

The proportion of all screened people who are correctly classified by the screening test is called?

Answer 13

Accuracy = (TP + TN)/All screened people

= (TP + TN)I(TP + TN + FP + FN)

Question 14

The proportion of screened people who have disease is called?

Answer 14

Prevalence = (TP + FN)/(TP + TN + FN + FP)

Prevalence can be estimated only if the entire population or a representative sample of the population is screened.

Question 15

In the screening test diagram, solid line represents?

Answer 15

People with no disease (solid line) are either correctly classified as TN or misclassified as FP.

Question 16

In the screening test diagram, dashed line represents?

Answer 16

Diseased people (dashed line) are either correctly classified as TP or misclassified as FN.

Question 17

Moving cutoff in the manner being considered by the CDC causes the number of false positives to
A. increase
B. decrease
C. remain unchanged
D. cannot be determined

Answer 17

A.

At Y, FP will increase as more well people are misclassified.

Question 18

Moving the cutoff in the manner being considered by the CDC causes the positive predictive value to
A. increase
B. decrease
C. remain unchanged
D. cannot be determined

Answer 18

B.

Although there will be more TP at Cutoff Y, there will be a large increase in numbers of FP. The ratio, TP/( TP + FP), will decrease. A positive test result will be less predictive of actual disease

Question 19

Moving the cutoff in the manner being considered by the CDC causes the accuracy to
A. increase
B. decrease
C. remain unchanged
D. cannot be determined

Answer 19

B.

X is the point of overlap and the point of maximal accuracy. Moving to Y will decrease accuracy.

Question 20

Moving the cutoff in the manner being considered by the CDC causes the sensitivity to
A. increase
B. decrease
C. remain unchanged
D. cannot be determined

Answer 20

A.

At Y, more diseased people will receive a (correct) positive test result. They will be TP. TP, the numerator for sensitivity, will increase while the denominator (total people with disease) will be unchanged.