Transcript Descriptive Epidemiology and Public Health

Descriptive Epidemiology
HSC4500
Module 4
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Types of Epidemiology
• Descriptive
• Examines the development and distribution of disease or
health-related events
• Analytic
• Determines the validity of hypotheses that attempt to
explain what descriptive epidemiology has revealed
• Experimental
• Purposeful manipulation of the independent variable to
study the subsequent effect on the dependent variable
Corresponding epidemiological study designs
• Descriptive
▫ If comparing populations:
 Ecological (correlational)
▫ If comparing Individuals:
 Case report
 Case series
 Cross sectional studies
• Analytic studies
▫ Observational
 Case-control
 Cohort (retrospective; prospective)
Experimental
 Randomized controlled trial (ex. testing new
pharmaceuticals)
 Field trial (high risk members of the population)
 Community trial (evaluate lifestyle interventions)
Descriptive vs. Analytic Epidemiology
Descriptive
• Usually the “first step”
• Utilized when relatively little is
known regarding the disease
or health-related event
• Utilizes previously collected
data
• Identifies potential
associations for further testing
(hypothesis generation)
• Involves the determination of
person, place, time (PPT)
Analytic
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Examines potential
associations revealed by
“new” data
Utilized when there exists
a greater understanding of
various aspects of the
disease or health-related
event
Examines the causality of
associations
Involves the determination
of the “why”
Descriptive Studies
• Often less expensive than analytic studies
• Often less time-consuming than analytic studies
• Most often used to explain:
▫ Patterns of disease occurrence
 Who becomes ill (or experiences the “health-event”)
 Who does not become ill (or avoids the “health-event”)
 In what populations are disease (or event ) rates highest
 In what populations are disease (or event) rates lowest
 Are temporal patterns of disease (or health-related event)
evident
▫ Beneficial in:
 Allocation of resources (administrators)
 Determination of risk factors (epidemiologists, providers)
 Development of effective programs
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Four main types of descriptive studies
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Ecologic studies
Case reports
Case series
Cross-sectional surveys
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• 1. Ecological studies:
• These are large-scale studies that provide
population-wide estimates of disease rates vs.
exposure status
• In other words: Data are often presented
comparing various countries around the world
• For example:
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Interpret these findings regarding
breast cancer mortality:
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2. Case reports and
3. Case series
• A case report involves a profile of a single
individual
• A case series involves a small group of
patients with a similar diagnosis
• These studies provide evidence for larger scale
studies
• They are hypothesis-generating
Ex. Case reports (case series)
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• “I saw three patients in the past 48 hours who reported
experiencing psychotic episodes after watching ‘Here Comes
Honey Boo Boo’ last Tuesday night”.
•What are your assumptions regarding this phenomenon?
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Note:
There is NO comparison group
NO detailed definition of either the exposure or the outcome
There is a suggestion that the exposure preceded the
outcome but NO proof.
• There is an implied relationship between the two events.
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4. Cross-sectional survey
(sometimes called prevalence survey)
• Conducted over a short period of time (usually a few days or
weeks) and the unit of analysis is the individual
• Like a “snapshot in time” of the characteristics of a group of
individuals
• There is no follow-up period
* A cross-sectional survey that is conducted on a regular or
scheduled basis is a serial survey
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• Example: A study of the severity of angina and
exercise showed that there was an inverse
relationship between the level of exercise and
reported chest pain severity.
• Note:
• It is NOT clear which is the exposure and which is
the outcome.
• Does lack of exercise cause chest pain?
• Or does chest pain lead to lack of exercise?
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Cross-sectional study
Strengths
• Can be used to study several associations at once
• Can be conducted over a short period of time
• Produce prevalence data
Weaknesses
• Unable to establish sequence of events
• Not feasible to use these studies to investigate rare
conditions (Wilson’s disease, 1-4 cases per 100,000)
• Potentially influenced by response bias (another lecture)
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Ex. Serial surveys
• Cross-sectional surveys that are routinely
conducted
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U.S. Census
Behavior Risk Factor Surveillance System
National Health Interview Survey
National Hospital Discharge Survey
The “Person” Factor:
All those characteristics about an individual that may explain the
reason for the development of a particular disease or the
occurrence of a particular health event:
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Age
Sex
Occupation
Immunization status
Co-morbidity
Medication(s)
Nutritional status
Socioeconomic factors
Religion
Hobbies
Pets
Travel
Personal Habits
Stress
Family dynamics
School environment
Genetics, etc., etc., etc.,
The “Time” Factor:
• Secular = the trend of a disease (or health event) over an
extended period of time; the pattern established during longterm occurrence
• Periodic = temporal interruption of the general trend of a secular
pattern
• Seasonal = cyclic variation in disease frequency by time of year &
season (environmental, occupational, recreational)
• Epidemic = increase in incidence above the expected in a defined
geographic area within a defined time period
Secular trend: Genital Warts; Initial Visits to
Physicians’ Offices, United States, 1966–2011
NOTE: The relative standard errors for genital warts estimates of more than 100,000 range from 18% to 30%.
SOURCE: IMS Health, Integrated Promotional Services ™. IMS Health Report, 1966–2011.
2011-Fig 53. SR
Periodic trend: Whooping Cough
Four-monthly admissions, 1954-1973
Chaturved, C., Descriptive Epidemiology
Seasonal Trend
Outpatient Influenza Visits 2006-2010
Percentage of visits for influenza-like Illness (ILI)* reported by the U.S. Outpatient Influenza-like
Illness Surveillance Network (ILINet),† by surveillance week --- United States, October 1, 2006--May
1, 2010, CDC influenza data
A Review: Endemic, Epidemic and Pandemic
• Endemic - The habitual presence (or usual occurrence) of a
disease within a given geographic area
• Epidemic - The occurrence of an infectious disease clearly in
excess of normal expectancy, and generated from a common or
propagated source
• Pandemic - A worldwide epidemic affecting an exceptionally
high proportion of the global population
Number of
Cases
of Disease
Time
Clustering
• Time/place clusters, or
• Disease clusters
• A group of cases that occur within a relatively close proximity
and with a distinct pattern of distribution
• Cluster analysis is particularly beneficial when examining rare
diseases or “unique” disease events.
Time/Place clustering analysis
• An inferential tool
• Nearly always ineffective in identifying causes of disease
• Often used to address public concern about environmental
hazards.
• Typically performed post hoc, and not as a result of a prior
hypothesis
• Describes disease events as they are distributed geographically.
• Geographical area divided into a series of equal square areas.
• If clustering occurs, probability of cause-effect relationship
increases  further epidemiological testing is pursued
Cluster analysis and disease mapping—why, when, and how? A step by step guide, BMJ 1996; 313 doi:
http://dx.doi.org/10.1136/bmj.
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Now:
Geographic Information Systems
• Per CDC:
• Collection of science and technology tools used to manage
geographic relationships and integrate information
• Help to analyze spatially-referenced data and make wellinformed decisions based on the association between the
data and the geography
• Refers to both the software and hardware that make up the
system of digital databases and layered maps.
• Plays an important part in health promotion and protection
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FLORIDA DEPARTMENT OF HEALTH Division of Public Health Statistics
& Performance Management, Florida Charts
Obesity
United States, 1987-1998
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Credits:
• Sexually Transmitted Disease: Surveillance 2011Centers for Disease
Control and Prevention National Center for HIV/AIDS, Viral Hepatitis, STD,
and TB Prevention Division of STD Prevention