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.

irockett@hsc.wvu.edu

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

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Age (in years)

Rat

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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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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