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Health events that are related in time
are what?
Define the three observational studies
and the use of each.
Define two types of interventional
studies and the advantages and
disadvantages of both.
What differences exist in urban and
rural health and what interventions
could improve health in these
In epidemiology, what are place variables?
Variations in infectious and chronic diseases from one
country to another may be attributed to what factors?
Urban diseases and causes of mortality are more
likely to be those spread by what?
What are increases and decreases in the frequency of
a disease within a year or over a period of several
What are gradual changes in the frequency of
diseases over long periods?
What indicates cases of disease that occur in a specific
geographic region?
Descriptive epidemiology provides information for what
In epidemiology, person variables may include what?
For both males and females, what type of cancer is the
leading cause of cancer mortality?
What factors may be considered when measuring
socioeconomic status?
Differences in the occurrence of diseases and adverse
health conditions in the population are known as what?
When the value of one variable increases and the value
of another variable decreases, the association is
what? And the reverse?
A graphic plotting of the distribution of cases by time
of onset is what kind curve?
A type of correlative association between the
magnitude of an exposure and effect is what kind of
A Threshold dose is what?
The category in a frequency distribution that has the
highest frequency of cases is what?
What type of variable that can have an infinite number of values within a
specified range?
What are the cycles of epidemiologic research?
With respect to derivation of hypotheses, a situation in which all of
the factors in two or more domains are the same except for a single factor is
known as:
Method of concomitant variation
Method of difference
None of the above
In a hypotheses, what type of association in which the frequency of an
outcome increases with the frequency of exposure to a factor is known as:
Method of concomitant variation
Method of difference
None of the above
Define the time period known as Latency.
Hill’s criteria of causality include what factors?
The temporality criteria needs what?
The web of causation model specifies what causal
The process of defining measurement procedures
for the variables used in a study is called what?
What is the process of passing from observations
and axioms to generalizations?
A confidence interval is what?
The ability of a study to demonstrate an association
if one exists is known as:
Explain what is meant by the cycle of epidemiologic
research. Identify three components of the cycle. Apply
the cycle to a hypothetical research project that would
examine teenage binge drinking.
Random assignment of subjects to study groups helps
to control for what?
What factor(s) distinguish study designs from one
Groups that are selected for an ecologic study might be
residents of a what?
What are kinds of outcome variables of an ecologic
study exist?
The Ecological fallacy is what?
Used in case-control studies, a type of indirect measure
of the association between frequency of exposure and
frequency of outcome is?
What are the advantages and disadvantages of casecontrol studies?
Define each of the following:
A.Prospective cohort study B.Case-control study
C.Cross-sectional study D.Retrospective cohort study
The ratio of the incidence rate of a disease in an exposed
group to the incidence rate of the disease in
a nonexposed group is what?
Advantages of cohort studies are?
Randomized controlled trials exclude what?
Features of randomized controlled trials include what?
Give an example of a hypothetical ecologic study. Name and
describe one advantage and one disadvantage of ecologic
Describe, briefly, the challenges to the validity of study
designs; relate these challenges to case-control studies,
cohort studies, and randomized controlled trials.
Chapter 5
Patterns of
Place, Time
Learning Objectives

Define the term descriptive epidemiology.
Give two examples of uses of descriptive epidemiology.
Compare three types of descriptive epidemiologic studies.
Describe the process of epidemiologic inference in the
context of descriptive epidemiology.
• Give two examples each of person, place, and time
variables and describe how they relate to the distribution of
health outcomes.
• Unequal distributions of health and disease in populations
• To determine why health conditions vary throughout
populations, one must answer the following questions:
– Who was affected?
– Where did the (health) event occur?
– When did the (health) event occur?
Definition: Descriptive Epidemiology
• The field of descriptive epidemiology classifies the
occurrence of disease according to the following variables:
– Person (who is affected)
– Place (where the condition occurs)
– Time (when and over what time period the condition has
Descriptive Epidemiologic Study
• A descriptive epidemiologic study is one that is
“…concerned with characterizing the amount and
distribution of health and disease within a population.”
Descriptive Epidemiology
• Provides valuable information for the following activities:
– Prevention of disease
– Design of interventions
– Conduct of additional research
Example of a Descriptive
Epidemiologic Study
• U.S. infants born in 2012 who were exclusively breastfed:
– About 43% of infants were breastfed during their first 3 months of
– About 22% were breastfed through the age of 6 months.
– From descriptive information, hypotheses for interventions to
increase breastfeeding can be derived.
Uses of Descriptive
Epidemiologic Studies
• Aims of descriptive epidemiology
– Permit evaluation of trends in health and disease
– Provide a basis for planning, provision, and evaluation of health
– Identify problems to be studied by analytic methods and suggest
areas that may be fruitful for investigation
Types of Descriptive
Epidemiologic Studies
• Case reports
• Case series
• Cross-sectional studies
Case Reports
• Accounts of a single occurrence of a noteworthy healthrelated incident or of a small collection of such events
• Examples:
– Bison encounters—Yellowstone National Park
– Adverse reactions due to cosmetic surgery in the United States
– Imported rabid dogs
Probable Non–Vector-borne Transmission of Zika Virus, Colorado,
USA Emerg Infect Dis. 2011 May; 17(5): 880–882.
Brian D. Foy,corresponding author Kevin C. Kobylinski, Joy L.
Chilson Foy, Bradley J. Blitvich, Amelia Travassos da Rosa,
Andrew D. Haddow, Robert S. Lanciotti, and Robert B. Tesh
Clinical and serologic evidence indicate that 2 American
scientists contracted Zika virus infections while working
in Senegal in 2008. One of the scientists transmitted this
arbovirus to his wife after his return home. Direct contact
is implicated as the transmission route, most likely as a
sexually transmitted infection.
Keywords: Zika virus, arbovirus, flavivirus, viruses,
mosquitoes, non–vector-borne transmission, sexually
transmitted infection, Colorado, expedited, dispatch
Case Series
• In comparison with a case report, a case series is a larger
collection of cases of disease, often grouped consecutively
and listing common features (i.e., characteristics of affected
• Example: Reported cases of primary meningoencephalitis
(121 cases reported between 1937 and 2007)
– Primary exposure source: fresh water in lakes and rivers
Cross-Sectional Studies
• A type of investigation “…that examines the relationship
between diseases (or other health-related characteristics)
and other variables of interest as they exist in a defined
population at one particular time”
• A type of prevalence study
• Exposures and outcomes measured at the same time
• Example of a cross-sectional study: The Behavioral Risk
Factor Surveillance System (BRFSS), which conducts an
ongoing survey of the health-related behaviors of U.S.
– An illustration of results from the BRFSS is a study of the
prevalence of healthy sleep patterns among Americans.
Epidemiologic Inferences from
Descriptive Data
• Descriptive epidemiology and descriptive studies provide a
basis for generating hypotheses.
• Epidemiologic inference tested in analytic research is
initiated with descriptive observations.
Figure 5-4 Process of epidemiologic inference.
Reprinted with permission from Aragón T. Descriptive epidemiology: Describing findings and generating hypotheses. Center for Infectious Disease Preparedness, UC Berkeley
School of Public Health. Available at: Accessed August 16, 2008.
Person Variables: Examples
• Covered in Chapter 5

Socioeconomic status
• Other examples

Marital status
Nativity (place of origin)
• Perhaps the most important factor to consider when
describing occurrence of disease or illness
– Age-specific disease rates usually show greater variation than
rates defined by almost any other personal attribute.
Examples of Age Associations
• The incidence of and mortality from chronic diseases
increase with age.
• Some infections (e.g., mumps and chickenpox) occur more
commonly during childhood.
• The leading cause of death among young adults is
unintentional injuries.
• Maternal age is associated with rates of diabetes and related
• Epidemiologic studies have shown sex differences in a wide
scope of health phenomena including morbidity and
• Examples:
– All-cause age-specific mortality rates are higher among males.
– Differences in cancer rates (e.g., cancers of the genital system).
Age-adjusted invasive cancer incidence rates per
100,000 for the 10 primary sites with the highest rates
within race- and ethnic-specific categories.
Source: Adapted and reprinted from U.S. Cancer Statistics Working Group. United States Cancer Statistics: 2003
Incidence and Mortality. Atlanta: U.S. Department of Health and Human Services, Centers for Disease Control
and Prevention and National Cancer Institute; 2006:220 and 222.
Figure 5-7 Leading sites of new cancer
cases and deaths—2016 estimates.
Reproduced from American Cancer Society. Cancer facts and figures 2016. Atlanta, GA: American Cancer Society; 2016, 20.
• Increasing diversity of the United States
Racial/ethnic distribution of the
population of the United States,
2006 estimates. Data for
individuals who declare only one
• Place of origin of the individual or his or her relatives
– Subdivisions include:
• Foreign-born
• Native-born
Racial and Ethnic Categories
• Five major categories in Census 2010:

Black or African American
American Indian and Alaska Native
Native Hawaiian and other Pacific Islander
• Census 2000 was the first to allow respondents to check a
multiracial category.
Other Considerations
• Somewhat ambiguous classification.
• Tends to overlap with nativity and religion.
• Some scientists propose that it is a social construct rather
than a biological construct.
• Used to track various health outcomes.
Race/Ethnicity (cont.)
• Examples of racial/ethnic differences in health
characteristics include the following:
– Lower frequency of asthma reported among Hispanics.
– Non-Hispanic whites and non-Hispanic blacks less frequently
report that they have no usual source of medical care than do
– Difficulties in physical functioning are highest among adults
classified as Native Hawaiians and Pacific Islanders.
– Incidence of gonorrhea is higher among non-Hispanic blacks than
other groups.
Socioeconomic Status (SES)
• Defined as a “descriptive term for a person’s position in
• Often formulated as a composite measure of the following
– Income level
– Education level
– Type of occupation
• A single dimension of SES (e.g., poverty level) may be
Socioeconomic Status (SES) (cont.)
• The social class gradient
– Strong, inverse association of SES with levels of morbidity and
– Those in the lowest SES positions are confronted with excesses of
morbidity and mortality from numerous causes.
• Example: Access to dental care
No dental visit in the
past year among
persons with natural
teeth, by age and
percent of poverty
level: United States,
2013 Milwaukee Health Report
Definition: Health Disparities
• Differences in the occurrence of diseases and adverse health
conditions in the population
– Example: cancer health disparities: “…adverse differences in
cancer incidence (new cases), cancer prevalence (all existing
cases), cancer death (mortality), cancer survivorship, and burden
of cancer or related health conditions that exist among specific
population groups in the United States.”
– African Americans (in comparison with other groups) have the
highest age-adjusted overall cancer incidence and death rates.
Place Variables

National (within-country)
Urban–rural differences
Localized patterns of disease
• World Health Organization (WHO) studies:
– Both infectious and chronic diseases show great variation from
one country to another.
• Climate, cultural factors, national dietary habits, and access
to health care affect disease occurrence.
• Variations in life expectancy (U.S. ranked number 42 in
Polio: An Example of an
International Variation
• Decreasing incidence globally
• In 2013, endemic polio remained in Afghanistan, Nigeria,
and Pakistan.
National (Within Country)
• Regional differences may affect the prevalence and
incidence of disease.
– Factors include:
• Climate
• Latitude
• Environmental pollution
• Example: Regional variations in stroke (see Figure 5-15)
Figure 5-15 Age-adjusted prevalence of
Reprinted from Centers for Disease Control and Prevention. Prevalence of Stroke—United States, 2006–2010. MMWR. 2012;61(20):382.
Urban–Rural Differences
• Urban and rural sections of the United States show
variations in morbidity and mortality related to
environmental and lifestyle issues.
– Urban example: Elevated occurrence of lead poisoning among
children who live in older buildings
– Rural example: Pesticide exposure and farming injuries among
agricultural workers
Localized Patterns of Disease
• Associated with specific environmental conditions that may
exist in a particular geographic area
• Examples:
– Lung cancer and radon gas
– Naturally occurring arsenic in water supply
– Presence of disease vectors: Dengue fever along the Texas–
Mexico border
Time Variables

Secular trends
Cyclic (seasonal) trends
Point epidemics
Secular Trends
• Refer to gradual changes in the frequency of disease over
long time periods
• Examples:
– Yearly suicide rates
• Higher among males than females
• U.S. females—suicides by suffocation increased
– Age-adjusted prevalence of hypertension (no secular trend shown)
Cyclic (Seasonal) Trends
• Cyclic trends are increases and decreases in the frequency
of a disease or other phenomenon over a period of several
years or within a year.
– Example 1: Severe weather events in the Atlantic basin
– Example 2: Mortality from pneumonia and influenza (peaks
during February)
Point Epidemics
• A point epidemic may indicate the response of a group of
people circumscribed in place to a common source of
infection, contamination, or other etiologic factor to which
they were exposed almost simultaneously.
– Example: Outbreak of Vibrio infections following Hurricane
Katrina in 2005
• “A closely grouped series of events or cases of a disease or
other health-related phenomena with well-defined
distribution patterns in relation to time or place or both…”
Clustering (cont.)
• Often used to describe aggregation of uncommon
conditions such as leukemia
• Clustering may reflect:
– Common exposure to an etiologic agent
– Chance occurrences
• Spatial clustering: The aggregation of events in a
geographic region
• Temporal clustering: The occurrence of events related to
2013 Milwaukee Health Report
• Descriptive epidemiology classifies the occurrence of
disease according to the variables of person, place, and
• Descriptive epidemiologic studies aid in generating
hypotheses that can be explored by analytic epidemiologic
• Descriptive studies include case reports, case studies, and
cross-sectional studies.
Chapter 6
Association and
Learning Objectives
• Describe the history of changing concepts of disease
• Compare and contrast noncausal and causal associations.
• Distinguish between deterministic and stochastic models of
• State at least three of the criteria of causality, giving
examples of each one.
• State one example of how chance affects associations
among variables.
• How trustworthy are media reports of epidemiologic
• How do we assess relationships between exposures and
health outcomes?
– How valid are observed associations?
– Applying the criteria of causality to evaluate associations
Disease Causality in History
• Witchcraft, demons, gods
• Environmental influences
• Theory of contagion
Cassius: “The fault, dear Brutus, is not in our
stars, But in ourselves, that we are underlings.“
Julius Caesar (I, ii, 140-141)
• Cassius, a nobleman, is speaking with his friend, Brutus,
and trying to persuade him that, in the best interests of the
public, Julius Caesar must be stopped from becoming
monarch of Rome. Cassius continues by reminding Brutus
that Caesar is just a man, not a god, and that they are equal
men to Caesar. They were all born equally free, and so why
would they suddenly have to bow to another man?
Influenza by Mass Hysteria
• Contagion theory is a theory of collective behavior which
explains that the crowd can cause a hypnotic impact on
individuals. The theory is first developed by Gustave Le
Bon in his book called “the crowd: a study of popular mind
in France” in 1885.
Disease Causality in History (cont.)
• Miasmas
• Spontaneous generation
• Germ theory
• In miasma theory, diseases were caused by the presence in the air of a
miasma, a poisonous vapour in which were suspended particles of
decaying matter that was characterised by its foul smell. The theory
originated in the Middle Ages and endured for several centuries. That
a killer disease like malaria is so named – from the Italian mala ‘bad’
and aria ‘air’ – is evidence of its suspected miasmic origins.
• In 19th-century England the miasma theory made sense to the
sanitary reformers. Rapid industrialisation and urbanisation had
created many poor, filthy and foul-smelling city neighbourhoods that
tended to be the focal points of disease and epidemics. By improving
the housing, sanitation and general cleanliness of these existing areas,
levels of disease were seen to fall, an observation that lent weight to
the theory.
• Spontaneous generation refers to an obsolete body of thought on the
ordinary formation of living organisms without de …
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