Unit 3

Question 1

The difference in risk (incidence) between exposed and unexposed groups:

Answer 1

AR(e) or RD (attributable risk exposed or risk difference)

Question 2

Attributable risk or risk difference applies to ___________ animals only.

Answer 2

exposed

Question 3

Ex: For every 100 animals exposed, expect an additional 20 cases.

Answer 3

Risk difference. Over baseline due to exposure only.

Question 4

The difference in risk (incidence) between the total population and unexposed group

Answer 4

Population attributable risk

Question 5

This expresses the amount of disease in the total population attributable to exposure.

Answer 5

PAR

Question 6

The proportion of incidence in exposed that is attributed to the exposure.

Answer 6

Attributable Proportion (exposed)

Question 7

AP(e) tells you what fraction (%) of disease in exposed is really due to:

Answer 7

exposure

Question 8

How do you calculate AP(e)?

Answer 8

(RR-1)/RR

Question 9

The proportion of incidence in population attributed to exposure

Answer 9

PAP (population attributable proportion)

Question 10

What fraction (%) of disease in the population is due to Exposure?

Answer 10

PAP

Question 11

How do you calculate PAP (population attributable risk)?

Answer 11

(incidence in population - incidence in E-)/incidence in population

Question 12

Which two measures of impact reference the exposed?

Answer 12

AR(e)/RD, AP

Question 13

Which measure of impact references the TOTAL population?

Answer 13

population attributable risk

Question 14

Which measure of impact references the population?

Answer 14

population attributable fraction

Question 15

Identify Koch’s postulates:

Answer 15

• it is present in all cases of the disease
• it does not occur as a fortuitous or non-pathogenic parasite
• it is isolated in pure culture from a case
• organism can be is repeatedly passaged, and induced the same disease in other animals

Question 16

What are the difficulties with Koch;s postulates in defining “cause”? Hint: There are seven.

Answer 16

1. multiple etiologic factors
2. multiple effects of a single cause
3. asymptomatic carriers (cholera)
4. non agent factors such as age
5. immunologic processes as cause of disease
6. host-agent, host-environment interactions
7. noninfectious causes of disease

Question 17

Identify how surgeon general changes the causation:

Answer 17

• consistency
• strength of association
• specificity of outcome, time, place, population
• temporality
• coherence

Question 18

Identify how hills criteria changes the causation:

Answer 18

surgeon general criteria plus:

• dose-response relationship
• plausible biologic mechanism
• experimental evidence to compliment

Question 19

Identify how Surgeon general/Hills criteria changes the focus of causation, and how they rely on factors apart from agent description for disease causation.

Answer 19

• acknowledged that clinically healthy individuals frequently tolerate pathogens quite well
• required proof of associated between hypothesized causal factor and disease
• accommodated non-infectious factors
• mandated temporal sequence
• dose-response relationship adds credibility

Question 20

the proportion (or fraction or probability) of cases of disease within a population

Answer 20

apparent prevalence

Question 21

Are results of the study applicable to the real population?

Answer 21

external validity

Question 22

Correct assessment of exposure and outcome in study groups

Answer 22

internal validity

Question 23

External validity requires __________, but internal validity does not require ______________.

Answer 23

internal validity; external validity

Question 24

a systematic error that results in an incorrect estimate in the relationship between exposure and disease:

Answer 24

bias

Question 25

If uncorrected, renders the results worthless:

Answer 25

bias

Question 26

Concerns the animals who participate and those that do not:

Answer 26

selection bias

Question 27

assessment of exposures and outcomes:

Answer 27

information bias

Question 28

To prevent this type of bias, comparisons must be drawn from the same population:

Answer 28

selection

Question 29

What are the three types of information bias?

Answer 29

observer, recall, misclassification

Question 30

differences in way information collected from E+ vs E- or D+ vs D-:

Answer 30

observer bias

Question 31

Those D+ may tend to recall exposures in greater detail than those in D-

Answer 31

recall bias

Question 32

When either E or D is not properly classified:

Answer 32

misclassification bias

Question 33

A “mixing” of effects:

Answer 33

confounding

Question 34

An extraneous variable that can wholly or partly account for an apparent association between an exposure and outcome:

Answer 34

confounding variable (confounder)

Question 35

correlated with the explanatory and response variable:

Answer 35

confounding variable

Question 36

restrict study subjects to avoid known confounding factors:

Answer 36

restriction

Question 37

Match pairs on a confounding variable so that confounding is distributed evenly between comparands:

Answer 37

matching

Question 38

When all classes, groups, or categories of a variable (whether exposure, outcome, or covariate) have the same error rate or probability of being misclassified for all study subjects.

Answer 38

non-differential misclassification

Question 39

Occurs when the proportions of subjects misclassified differ between the study groups

Answer 39

differential misclassification