1. What is a population? What is population health?
Epidemiology matters: a new introduction to methodological foundations
Chapter 2

2. Epidemiology Matters – Chapter 2
A brief introduction to the graphical notation used in Epidemiology Matters
Epidemiology Matters – Chapter 2

3. Epidemiology Matters – Chapter 2
Diseased
Non-diseased
Epidemiology Matters – Chapter 2

4. Epidemiology Matters – Chapter 2
Set of individuals
100 individuals
20 diseased individuals
Epidemiology Matters – Chapter 2

5. Multiple sets of individuals
Epidemiology Matters – Chapter 2

6. Epidemiology Matters – Chapter 2
Defining a population of interest
Dynamic versus stationary populations
Summary
Epidemiology Matters – Chapter 2

7. Epidemiology Matters – Chapter 1
Seven steps
Define the population of interest
Conceptualize and create measures of exposures and health indicators
Take a sample of the population
Estimate measures of association between exposures and health indicators of interest
Rigorously evaluate whether the association observed suggests a causal association
Assess the evidence for causes working together
Assess the extent to which the result matters, is externally valid, to other populations
Epidemiology Matters – Chapter 1

8. Epidemiology Matters – Chapter 2
Defining a population of interest
Dynamic versus stationary populations
Summary
Epidemiology Matters – Chapter 2

9. Defining a population of interest
A population is a collection of individuals, at moments in time, defined by at least one organizing characteristic
The definition of a population has implications for analysis, interpretation, and generalizability of results from epidemiologic studies .
Epidemiology Matters – Chapter 2

10. Two axes of population definitions
Populations are defined by eligibility criteria
Populations are defined by whether individuals move in and out of eligibility; i.e., populations can be dynamic or stationary .
Epidemiology Matters – Chapter 2

11. What could be eligibility criteria?
Geographic area and time period of interest
Characteristics of persons, events, or exposures for which health-related factors are of interest
Factors that promote successful study completion
Epidemiology Matters – Chapter 2

12. Population, defined by geographic space and time
Epidemiology Matters – Chapter 2

13. Dynamic population of Farrlandia over 1 year
Epidemiology Matters – Chapter 2

14. Dynamic population of Farrlandia over 1 year
Epidemiology Matters – Chapter 2

15. Dynamic population of Farrlandia over 1 year
Epidemiology Matters – Chapter 2

16. Examples of populations, defined by characteristic, event, or exposure
If we are interested in understanding determinants of neonatal health, the population of interest is all newborn infants. Therefore, the defining event for inclusion is date of birth, and eligible individuals for population can be those within a year of their birth.
Pregnant women
Individuals over the age of 65
Individuals exposed to a natural or human-made disaster
Individuals of certain races or ethnicities
Individuals subject to particular laws 
Epidemiology Matters – Chapter 2

17. Epidemiology Matters – Chapter 2
An example
After the World Trade Center 2001 attack, a study considered neonatal outcomes among offspring of women in California who gave birth six months after the attack comparing them to women who gave birth six months before the attack
This study therefore defined population of interest defined by
a. Event or exposure = pregnancy
b. Geographic location = California
c. Time period = six months before and after September 11, 2001
Epidemiology Matters – Chapter 2

18. Populations, defined by study considerations
Population of interest may be select group collected specifically to achieve successful study
Good responders to our surveys
Likely to continue to attend the health facility for follow-up visits
Individuals who are healthy so that they are unlikely to die during the course of the study outside scope of inquiry
Epidemiology Matters – Chapter 2

19. Epidemiology Matters – Chapter 2
An example
The Women’s Health Initiative is a study that assesses health benefits and risks of hormone replacement therapy after menopause. Eligibility is limited to women who had undergone menopause.
The study excludes
a. Women with a history of certain medical conditions
b. Women who were unlikely to be adherent to study protocol
c. Women who failed to meet other criteria
Epidemiology Matters – Chapter 2

20. Epidemiology Matters – Chapter 2
Defining a population of interest
Dynamic versus stationary populations
Summary
Epidemiology Matters – Chapter 2

21. Dynamic vs stationary populations
Dynamic eligibility criteria for the population: allow movement in
and/or out of the population. For example, people may move out of geographic region and no longer be considered part of the population of interest.
Stationary eligibility criteria for the population: do not allow movement in and/or out of the population. For example, population may include all those born on a particular date only and follow them forward in time, never losing any nor adding others.
Epidemiology Matters – Chapter 2

22. Epidemiology Matters – Chapter 2
Defining a population of interest
Dynamic versus stationary populations
Summary
Epidemiology Matters – Chapter 2

23. What is a population? What is population health?
Epidemiology is concerned with understanding the health of populations
Populations of interest can be defined by geography, space, time or by characteristics of participants or of events of interest
Regardless of eligibility criteria, population may be dynamic or stationary
Careful definition of the population base from which we conduct an epidemiologic study underlies many of the core methods in epidemiology
Epidemiology Matters – Chapter 2

24. Epidemiology Matters – Chapter 1
Seven steps
Define the population of interest
Conceptualize and create measures of exposures and health indicators
Take a sample of the population
Estimate measures of association between exposures and health indicators of interest
Rigorously evaluate whether the association observed suggests a causal association
Assess the evidence for causes working together
Assess the extent to which the result matters, is externally valid, to other populations
Epidemiology Matters – Chapter 1

25. Epidemiology Matters – Chapter 1
epidemiologymatters.org
Epidemiology Matters – Chapter 1