DESCRIPTIVE EPIDEMIOLOGY for Public Health Professionals Part 4 Ian R.H. Rockett, PhD, MPH Department of Community Medicine West Virginia University School of Medicine Prepared under the auspices of the Southeast Public Health Training Center, University of North Carolina, Chapel Hill,

From MEASUREMENT to DESCRIPTION From MEASUREMENT to DESCRIPTION

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

United States Suicide Rates by Age, Sex, and Racial Group, Data accessed through CDC Wonder:

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 Southeast Asian Refugees (1992). American Journal of Epidemiology 135(12): 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:

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 FORMULATION The Bridge to Analytic Epidemiology HYPOTHESIS FORMULATION The Bridge to Analytic 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 in I.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 Cure Control Disability Death Disease Onset SymptomsDiagnosisTherapy Care 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,

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

Years of Healthy Life vs. Years of Life, United States, 1990 Age (in years) Years

To Access Some Online Epidemiology Texts Visit TableOfContents.htm ulation_Bulletin1&template=/ContentManagem ent/ContentDisplay.cfm&ContentID= ulation_Bulletin1&template=/ContentManagem ent/ContentDisplay.cfm&ContentID=9854