Chapters 15 & 16

Question 1

How is screening defined?

Answer 1

The presumptive identification of an unrecognized disease or defect by the application of tests, examinations, or other procedures which can be applied rapidly.

Question 2

What is the purpose of primary prevention?

Answer 2

prevents disease from occurring; goal is to reduce incidence

Question 3

What is the purpose of secondary prevention?

Answer 3

Delays onset and duration of clinical disease. Goal is to improve survival.

Question 4

What is the purpose of tertiary prevention?

Answer 4

Slows disease progression; reduces disease sequelae; goal is to improve survival

Question 5

What are the characteristics of diseases appropriate for screening?

Answer 5

Disease is serious with severe consequences
Treatment is more effective at an earlier stage
Disease has a detectable preclinical phase
DPCP is fairly long and prevalent in the target population

Question 6

What are the main characteristics of a screening test?

Answer 6

Validity
Reliability
Source of Test Errors
Criterion of Positivity
Sensitivity
Specificity

Question 7

What is reliability?

Answer 7

the ability of a test to give the same result on repeated testing

Question 8

What is validity?

Answer 8

the ability of a test to correctly identify individuals who do and do not have preclinical disease

Question 9

What is sensitivity?

Answer 9

the probability that a test correctly classifies positive individuals who have the preclinical disease

Question 10

What is specificity?

Answer 10

the probability that a test correctly classifies individuals without preclinical disease as negative

Question 11

What is lead time?

Answer 11

The amount of time that the disease diagnosis is advanced by screening.

Question 12

What is a screening program?

Answer 12

A set of procedures for early detection and treatment of a disease that is available to a population

Question 13

What is a predictive value?

Answer 13

the main way to measure a screening program’s feasibility.

Two components:

Predictive Value Positive (PVP) - proportion of individuals with a positive test who have the preclinical disease -

Predictive Value Negative (PVN) - the proportion of individuals without the preclinical disease who test negative

Question 14

What is lead time bias?

Answer 14

Lead time bias refers to a distortion overestimating the apparent time surviving with a disease caused by bringing forward the time of its diagnosis.

Question 15

What is length bias sampling?

Answer 15

Length time bias is an overestimation of survival duration due to the relative excess of cases detected that are asymptomatically slowly progressing, while fast progressing cases are detected after giving symptoms.

Question 16

What is volunteer bias?

Answer 16

The decision to be screened is influenced by a person’s health awareness, which may be related to his / her subsequent morbidity and mortality

Question 17

What are typical outcomes used to measure the success of a screening program?

Answer 17

process measures
survival
shift in stage distribution
overall mortality
cause specific mortality

Question 18

What is the usual effect of developing a widespread screening program?

Answer 18

The incidence rate of the target disease increases at first and then declines as a result of the earlier diagnosis of cases

Question 19

What was the result of implementing breast cancer screening through the 1990s?

Answer 19

Reduced the risk of dying by about 30% among women ages 50 to 69 after 10-12 years of follow up.

Question 20

Describe the prevention timeline

Answer 20

Question 21

Describe the effects of screening on prostate cancer

Answer 21

Question 22

How do epidemiologists Rothman, Greenland, and Lash define a “cause”?

Answer 22

an event, condition, or characteristic that preceded the disease onset and that, had the event / condition / characteristic been different… the disease would not have occurred at all or would not have occurred until some later time.”

Question 23

When is an association considered valid?

Answer 23

When 3 other alternative explanations (bias, confounding, random error) have been eliminated / disproven

Question 24

What are the attributes of a cause according to Susser?

Answer 24

Association, time order (cause leads to effect), and direction (x leads to y but not vice versa)

Question 25

What are other attributes of causes?

Answer 25

They may include host / environmental factors

They may be passive or active

They may be either positive or negative associations

Question 26

Who introduced the idea of the 4 humours?

Answer 26

Hippocrates (circa 400 BC)

Suggested that imbalances in these were caused by changes in seasons, elements, nature, and personal habits

Question 27

Who introduced Germ Theory?

Answer 27

Louis Pasteur, Miles Berkeley, and many others in the mid 1800s

Question 28

What did people believe caused illness prior to germ theory?

Answer 28

(prior to the 1800s) sin

(early 1800s) spontaneous generation or foul clouds (miasmas)

Question 29

What were Henle and Koch’s postulates (mid to late 1800s)?

Answer 29

1. The agent must be demonstrable in every case of the disease; 2. The agent is not present in other diseases; 3. After isolation in culture, the agent must be able to produce the disease in experimental animals; and (added by Koch) 4. The agent can be recovered from the experimental animal.

Question 30

What are limitations of Henle / Koch’s Postulates?

Answer 30

They apply well to infectious disease but not to non-communicable diseases (particularly postulate 1)

Question 31

When were the modern “causal criteria” first introduced?

Answer 31

In the 1950s and 1960s; 5 were presented in the 1964 Report of the Advisory Committee to the Surgeon General on Smoking and Health (to prove smoking causes lung cancer)

Question 32

What is the best known criteria for assessing causation?

Answer 32

1965 - Sir Austin Bradford Hill’s 9 criteria / guidelines

Question 33

What are Hill’s causation critera?

Answer 33

1. strength of association
2. consistency
3. specificity
4. temporality
5. biological gradient
6. plausibility
7. coherence
8. experiment
9. analogy

Question 34

Should we wait until proving causation to recommend public health strategies?

Answer 34

No - we have a moral obligation to suggest sooner

Question 35

How does Rothman define “sufficient cause?”

Answer 35

a complete causal mechanism that inevitably produces disease

(not a single factor but a minimal set of factors - this may include the presence of causative exposures and lack of preventative exposures)

Question 36

What is a component cause?

Answer 36

Each single factor in a sufficient cause

Question 37

What is an example of Rothman’s 1970 sufficient component theory?

Answer 37

a person cannot get AIDs unless he/she is susceptible AND is exposed to HIV AND has unprotected intercourse (etc.)

Question 38

What are important factors of sufficient component theory?

Answer 38

1 disease may have several different “cause constellations”

blocking the action of a single cause component stops the completion of the sufficient cause and thereby prevents disease from occurring by that pathway

completion of a sufficient cause is synonymous with biological disease onset

component causes may act far apart in time

Question 39

Describe Rothman’s Causal Pies

Answer 39

Question 40

Describe the web of causation for Lead Poisoning

Answer 40

Question 41

Describe different types of Dose Response relationships

Answer 41