Chapter 2

Question 1

Environmental topics for epidemiology

Answer 1

1. Air Pollution
2. Chemicals
3. Climate Change
4. Water Pollution

Question 2

What Is Environmental Epidemiology?

Answer 2

• Study of diseases and health conditions (occurring in the population) linked to environmental factors
• Exposures usually involuntary

Question 3

Epidemiology’s Contributions to Environmental Health

Answer 3

• Concern with populations
• Use of observational data
• Methodology for study designs
• Descriptive and analytic studies

Question 4

Concern with Populations

Answer 4

• Environmental epidemiology studies the entire population.
• Sometimes called population medicine

–Example: Is lung cancer mortality higher in areas with higher concentrations of “smokestack” industries?

Question 5

Use of Observational Data

Answer 5

• Epidemiology is primarily an observational science.
• Takes advantage of naturally occurring situations to study the occurrence of disease

Question 6

Methodology for Study Designs

Answer 6

•Characteristic study designs used frequently in environmental epidemiology

–Cross-sectional

–Ecologic

–Case-control

Cohort

Question 7

Methodology for Study Designs

Answer 7

•Characteristic study designs used frequently in environmental epidemiology

–Cross-sectional

–Ecologic

–Case-control

–Cohort

Question 8

Two Classes of
Epidemiologic Studies

Answer 8

•Descriptive

–Depiction of the occurrence of disease in populations according to classification by person, place, and time variables

•Analytic

–Examines causal (etiologic) hypotheses regarding the association between exposures and health conditions

Question 9

Measures of Disease Frequency

Answer 9

• Prevalence
• Point prevalence
• Incidence
• Incidence rate
• Case fatality rate

Question 10

Prevalence

Answer 10

•Number of existing cases of or deaths from a disease or health condition in a population at some designated time

Question 11

Point Prevalence

Answer 11

•All cases of or deaths from a disease or health condition that exist at a particular point in time relative to a specific population from which the cases are derived

Question 12

Formula for Point Prevalence

Answer 12

Point prevalence =

Number of persons ill / Total number in the group

at a point in time

Question 13

Incidence

Answer 13

•Occurrence of new disease or mortality within a defined period of observation (e.g., a week, month, year, or other time period) in a specified population

Question 14

Formula for Incidence Rate

Answer 14

Incidence rate =

Number of new cases over a time period / Average population at risk during the same time period

x multiplier (e.g., 100,000)

Question 15

Case Fatality Rate (CFR)

Answer 15

•Measure of the lethality of a disease

Question 16

Formula for Case Fatality Rate (CFR)

Answer 16

CFR(%) =

Number of deaths due to disease “X” /
Number of cases of disease “X”

x 100 during a time period

Question 17

Major Historical Figure:
Sir Percival Pott (1714–1788)

Answer 17

• London surgeon
• Thought to be the first individual to describe environmental cause of cancer

–Chimney sweeps had high incidence of scrotal cancer due to contact with soot.

Question 18

Major Historical Figure:
John Snow

Answer 18

• English anesthesiologist
• Linked cholera outbreak in London to contaminated water from the Thames River in the mid-1800s
• Employed a “natural experiment,” a methodology used currently in studies of environmental health problems

Question 19

Odds Ratio (OR)

Answer 19

• Measure of association between exposure and outcome
• Used in case-control studies
• Exposure-odds ratio

–“ratio of the odds in favor of exposure among the cases [A/C] to the odds in favor of exposure among non-cases [the controls, B/D]”

Question 20

Odds Ratio Table

Question 21

Odds Ratio Equation

Answer 21

OR= (A/C)/(B/D) = AD/BC

Note: OR >1 (when statistically significant) suggests a positive association between exposure and disease or other outcomes.

Question 22

Relative Risk (RR)

Answer 22

•Ratio of the incidence rate of a disease or health outcome in an exposed group to the incidence rate of the disease or condition in a nonexposed group

Question 23

Relative Risk (RR) Table

Answer 23

TABLE 2.3 Table for a Cohort Study

Question 24

RR Equation

Answer 24

Notes: When an association is statistically significant:

RR > 1 indicates that the risk of disease is greater in the exposed group than in the nonexposed group.

RR < 1 indicates a possible protective effect.

Question 25

Study Endpoints

Answer 25

• Self-reported
• Physiologic or clinical examinations
• Mortality

Question 26

Figure 2.11 The epidemiologic triangle

Question 27

What Is the
Epidemiologic Triangle?

Answer 27

• Used to describe causality of infectious diseases
• Provides framework for organizing the causality of other types of environmental problems

Question 28

Environment in the “Triangle”

Answer 28

• Domain in which disease-causing agents may exist, survive, or originate
• Consists of “All that which is external to the individual human host.”

Question 29

Host in the “Triangle”

Answer 29

•“person or other living animal, including birds and arthropods, that affords subsistence or lodgment to an INFECTIOUS AGENT under natural conditions”

Question 30

Agent in the “Triangle”

Answer 30

•“factor (e.g., a microorganism, chemical substance, form of radiation, mechanical, behavioral, social agent or process) whose presence, excessive presence, or (in deficiency diseases) relative absence is essential for the occurrence of a disease”

Question 31

Causality

Answer 31

•Certain criteria need to be taken into account in the assessment of a causal association between an agent factor (e.g., exposure) and a disease (e.g., outcome).

Question 32

Bias in Environmental
Epidemiologic Studies

Answer 32

• Definition of bias
• The healthy worker effect
• Confounding

Question 33

Limitations of Epidemiologic Studies

Answer 33

• Long latency periods
• Low incidence and prevalence
• Difficulties in exposure assessment
• Nonspecific effects