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DESCRIPTIVE EPIDEMIOLOGYDESCRIPTIVE EPIDEMIOLOGYfor Public Health Professionals for Public Health Professionals
Part 4Part 4Ian R.H. Rockett, PhD, MPH
Department of Community Medicine
West Virginia University School of Medicine
Prepared under the auspices of the Prepared under the auspices of the Southeast Public Health Training Southeast Public Health Training Center, University of North Carolina, Center, University of North Carolina, Chapel Hill, 2005.Chapel Hill, 2005.
From From MEASUREMENT MEASUREMENT
to to DESCRIPTIONDESCRIPTION
Descriptive Epidemiology
Magnitude of the Problem - how big?
Person, Place, and Time - who, where, and when?
Magnitude of the Problem
Injury Deaths Worldwide by Leading Causes and Intent, 1990
Person Place and
Time
PERSON
Demographic characteristics e.g. age, sex, race, marital status, number of children
Socioeconomic characteristics e.g. social class, employment status, occupation
Life style/behavior e.g. drinking alcohol/smoking marijuana and driving
Figure 1. United States Suicide Rates by Age, Sex, and Racial Group, 1999-2001
0
10
20
30
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15-19 20-24 25-34 35-44 45-54 55-64 65-74 75-84 85+
Age (in years)
Rat
e p
er 1
00,0
00
White Male Black Male White Female Black Female
United States Suicide Rates by Age, Sex, and RacialGroup, 1999-2001
Data accessed through CDC Wonder: http://wonder.cdc.gov/mortICD10J.html
PLACE
Are the disease or injury cases: geographically confined or
pervasive?
clustering around known potential pathogens, toxins, or other hazards?
TIME
Are disease (injury) rates or case numbers variable or constant?
Do rates or case numbers vary seasonally?
Is the disease attributable to a point source of infection or propagated transmission?
Source: McAuley, J. et al. A Trichinosis Outbreak Among SoutheastAsian Refugees (1992). American Journal of Epidemiology 135(12):1404-1410. Reproduced in Rockett, I.R.H. Population and Health: An introduction toEpidemiology(1999). Population Bulletin 54(4):23.
Descriptive Study Designs
Correlational (Ecological) Study – uses data from entire populations to compare disease/injury frequencies in relation to putatively harmful (or beneficial) exposures during the same period of time or at different points in time (typically use secondary published data like vital statistics, censuses and national health surveys)
Source: Len Evans. Traffic Crashes. American Scientist 90 (3); 2002: 246. http://www.dushkin.com/text-data/articles/34749/body.pdf
Case Report - most basic type of descriptive study of individuals, comprising a careful detailed report by one or more clinicians that profiles a single patient’s case
Case Series – describe characteristics of a number of patients with a given disease
Cross-Sectional Studies – the status of an individual with respect to the presence or absence of both exposure and disease/injury of interest is assessed at one point in time (if the timing of each cannot be differentiated, this too qualifies a study as cross-sectional)
HYPOTHESIS HYPOTHESIS FORMULATIONFORMULATION
TheThe Bridge to Bridge to Analytic EpidemiologyAnalytic Epidemiology
Method of Difference
Examines differences among groups for clues as to why
the groups’ disease rates or other health problems vary
Source: Ian R.H. Rockett. Population and Health: An Introduction to Epidemiology. Second edition. Population Bulletin 54(4); 1999: 17.
Method of Agreement
Looks for commonality in
groups that manifest the same health
problem
Method of Concomitant
Variation
Traces how exposure to a hazard varies in
relation to disease or other health problems
Problem of Chronic Disease Latency
Source: Doll, R. Etiology of Lung Cancer (1955). Advances in Cancer Research 3;1955:1-50. Reproduced inI.R.H. Rockett. Population and Health: An introduction to Epidemiology, Second edition.Population Bulletin,54(4);1999: 25.
Early Intervention in the Natural History of Disease
HEALTH OUTCOMES
CureControl
DisabilityDeath
Disease Onset
Symptoms Diagnosis TherapyCare Seeking
Good Health
Early detection through Screening
Method of Analogy
Involves applying a model that characterizes one kind of
disease or injury to another kind
Method of Detection of Conflicting Observations
Pellagra, commonly regarded as a
communicable disease, produced skin eruptions
and digestive and nervous disorders
Joseph Goldberger, 1874-1929
•
Laboratory Observations
Even though lacking research experience, Dr. Barry Marshall and Dr.
Robin Warren were able to link peptic ulcers to the bacterium Helicobacter
Pylori
Source: University of Western Australia. UniView 22(1);2003:4.
ANALYTIC EPIDEMIOLOGY
Addressing the why question
From Epidemiology to
Population Health
Health Life Expectancy: Life Years vs. Years of Healthy Life in the United Sates, 1990
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1000
1500
2000
2500
3000
0-10 10 to 20 20-30 30-40 40-50 50-60 60-70 70-80 80+
YL YHL
Years of Healthy Life vs. Years of Life, United States, 1990
Age (in years)
Yea
rs
To Access Some Online Epidemiology Texts
Visit
http://www.epidemiolog.net/evolving/ TableOfContents.htm
http://www.prb.org/Template.cfm?Section=Population_Bulletin1&template=/ContentManagement/ContentDisplay.cfm&ContentID=9854
http://bmj.com/epidem/epid.html