1. Epidemiology Kept Simple
Chapter 4
Descriptive Epidemiology
Gerstman

2. What is Descriptive Epi?
Exploratory
Hypothesis generation
Often uses standing data sources
Analytic epi
Tests specific causal hypotheses
Quantifies effects
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Ch 4: Descriptive Epi

3. Descriptive – Analytic Spectrum
Hypothesis Generating
Standing data sources
Analytic
Hypothesis Testing
Ad hoc data collection
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4. Descriptive Epi Variables
Exploration of occurrence by
person variables
place variables
time variables
I keep six honest serving men
They taught me all I know;
Their names are what and why and when
And how and where and who.
(Kipling)
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5. Sources of Descriptive Data
Case series (no denominator)
Surveillance systems
Active (scrutiny of population for all cases)
Passive (voluntary or mandatory reporting of cases as they are “naturally” detected)
Morbidity Surveys (NCHS)
Mortality Data (death certificates + census)
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6. One of keys clues leading to discovery of AIDS: Case Series
5 cases of Pneumocystis pneumonia in previously healthy young men
Pharmacist noticed unusual requests for antifungal drug pentamidine
STD experts noted cellular immune dysfunction
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7. Weiss’s Uterine Cancer Data Hypothesis: unopposed estrogen and uterine cancer
SEER data – active surveillance of cancer occurrence
Increases in uterine cancer
Parallel increases in the use of estrogen prescribed for symptoms of menopause and osteoporosis
Analytic epi and animal studies corraborated descriptive findings
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8. FDA Adverse Event Report System Suprofen / Flank-Pain Example
Passive collection of Dr. & consumer reports
Stimulate reporting system with Dear Doctor letters
Drug was ultimately removed from the market
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9. Person Variables
Characteristics, attributes, and behaviors of individuals
Illustration: Recreational injuries per 1000 person-years by age and gender
Gerstman
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10. Place Variables Where people live and work
Illustration: Age-adjusted breast cancer mortality in 23 countries, 1958–59
Gerstman
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11. Time Variables Example: Epidemic curves Sporadic Endemic
Point epidemic
Propagating epidemic
Gerstman
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12. Morbidity and Mortality Studies
See pages 4 – 5
NCHS publications and websites
NCHS databases
Health United States (one of my favorites)
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13. Ecological Studies
Unit of observation is the aggregate (cannot disaggregate data to the individual level)
E.g., regional correlations
Note different use of the term “ecology”
Readily available data sources
Often useful for hypothesis generation
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14. The Ecological Fallacy
Consists in thinking that an association seen in the aggregate holds true for individuals when in fact it does not
A form of “confounding” (Spurious association caused by extraneous factors)
Historical example: cholera mortality associated with elevation correlation used to support miasma theory
Water Source
Elevation
Cholera
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15. Multilevel analysis Combines individual and aggregate-level variables
Untangle relations between individual- and aggregate-level risk factors
Types of aggregate-level variables (NR)
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16. Study Chapter 4 for additional details and illustrative examples
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17. In class activity: Exercise 4.1
Table 4.5 displays a correlation matrix from an ecological study on cigarette consumption and selected cancers. Interpret the results & generate causal hypotheses.
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18. In class activity: Exercise 4.3 Durkheim, 1895
Social explanations require comparisons
Comparisons require classification
Classification requires definition of facts to be classified, compared, and explained
Durkheim differentiated between true social science & notiones vulgares (popular concepts of social phenomena without scientific reflection).
Emile Durkheim
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19. Notiones Vulgares
Durkheim warned against notiones vulgares — the idea that crudely formed concepts of social phenomena without scientific reflection produce only false knowledge: just as alchemy had preceded chemistry and astrology had preceded astronomy, social reflection merely foreshadows true social science.
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20. Le Suicide (1897)
Durkheim’s seminal work Le Suicide (1897) considered many potential risk factors for suicide, including psychopathological states, race, heredity, climate, season, imitative behavior, religion, social instability, and a host of other social phenomena.
Painting by Édouard Manet
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21. Table 4.6 (p. 122)
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22. Questions
Based on these data, list four observations about the potential effects of marriage on suicide.
Present an alternative explanation, other than the effect of marriage, for the associations you noted in part (A).
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