DESCRIPTIVE EPIDEMIOLOGYDESCRIPTIVE EPIDEMIOLOGYfor Public Health Professionals for Public Health Professionals

Part 2Part 2Ian R.H. Rockett, PhD, MPH

Department of Community Medicine

West Virginia University School of Medicine

Prepared under the auspices of Prepared under the auspices of the Southeast Public Health the Southeast Public Health Training Center, University of Training Center, University of North Carolina, Chapel Hill, 2005.North Carolina, Chapel Hill, 2005.

irockett@hsc.wvu.edu

DISEASEDISEASE

andand

INJURY MODELSINJURY MODELS

The Epidemiologic Triad

HOST

AGENT ENVIRONMENT

Agent

Host Environment

Vector

Factors involved in the Natural History of Disease

Epidemiologic Triad applied to Injury

Levels of Prevention

Primary

Secondary

Tertiary

The Haddon Matrix

Factors

Phases

Human Factors

Agent or

Vehicle

Physical Environment

Sociocultural Environment

Pre-event

Event

Post-event

Source: Ian R.H. Rockett. Injury and Violence: A Public Health Perspective. Population Bulletin 53(4); 1998: 18. Adapted from G.S Smith and H. Falk, Unintentional Injuries. American Journal of Preventive Medicine 3(5) Supplement; 1997:143-163.

Haddon Matrix (bombings)

Strengthen public healthinfrastructure

Emergencycall boxes??

Train people in first aid

Post-event

Strengthen norms for rescue volunteers

Shatter-proof glass

Slower actingexplosives

Wear protective clothes

Event(explosion & collapse

Reduce animosity

No vehicle zones

Detectablebombs

Teach to recognizesuspiciouspersons

Pre-event

Social Environ.

Physical Environ.

Vehicle/Vector (bomb / bomber)

PersonFactors

Phases

The Wheel of Causation

Social Environment

Genetic Core

Physical Environment

Biological Environment

Host (human)

Web of Causation

-- de-emphasizes the disease agent and allows for multifactorial causes

Web of Causation applied to Myocardial Infarction

Wider Application of the Web

Epidemiologic Triad (devised to enhance search for understanding communicable disease)

Web of Causation (devised to address chronic disease – can also be applied to communicable disease)

DATA SOURCES DATA SOURCES

and and DEVELOPMENT DEVELOPMENT

of of INFORMATION INFORMATION

Natural History of Disease/Injury and Related Data Sources

HEALTH OUTCOMES

CureControl

DisabilityDeath

Disease Onset

Symptoms Diagnosis TherapyCare Seeking

Good Health

Interviews

Medical Records

Hospital/ED Records

SELECTED DATA

SOURCES

Death CertificatesMedical Examiner aaaaRecords

Screening Test Results

Mortality (Death) Records

Source: Leon Gordis, Epidemiology, 2d edition; Philadelphia, PA: Saunders, 2000: 50.

Uncertainty in Reported Cause of Death

Michael Alderson (1988) identified four areas where uncertainties or inaccuracies can arise in reporting causes of death:

1) incorrect diagnosis (last attending physician and/or autopsy)

2) incorrect completion of death certificate3) inaccurate processing and publication of

the mortality statistics4) invalid classification of diseases/injuries

Multiple Cause-of-Death

Analysis

Distinguishing Natural from Other Causes of

Death

Use of Medical Examiner and Coroner Records to

supplement Death Certificate Data

Need to rule out homicide, suicide or “accident” , i.e., unintentional injury, before a death can be validly attributed to natural causes.

Homicide or SIDS?

Disease and Injury Mortality are only the Tip of the Iceberg

Morbidity Data Sources

General Sources of Morbidity Data1. Disease reporting -- communicable diseases, cancer registries

2. Data accumulated as a by-product of insurance and prepaid medical care plansa. Group health and accident insuranceb. Prepaid medical care plansc. State disability insurance plansd. Life insurance companiese. Hospital insurance plansf. Railroad Retirement Board

3. Tax-financed public assistance and medical care plansa. Public assistance, aid to the blind, aid to the disabledb. State or federal medical care plansc. Armed Forcesd. Veterans Administration

General Sources of Morbidity Data continued. . .

4. Hospitals and clinics

5. Absenteeism records -- industry and schools

6. Pre-employment and periodic physical examinations in industry and schools

7. Case-finding programs

8. Selective service records

9. Morbidity surveys on population samples (e.g., National Health Survey, National Cancer Surveys)

Source: Leon Gordis. Epidemiology. Third edition. Philadelphia, PA, 2004: 37.

ICD and ICD-CM

The International Statistical Classification of Diseases and Related Health Problems (ICD) can be used for coding and classifying mortality data from death certificates

The International Classification of Diseases Clinical Modification (ICD-CM) can be used to code and classify disease and injury morbidity data from inpatient and outpatient records

Dynamic Classification

Causes of disease, injury and disability may wax and wane. ICD needs to be flexible, especially in responding to new circumstances:

e.g. SARS, terrorism attributable health outcomes as from such varied causes as asphyxiation, chemical burns, falls and jumping from buildings, and suicide and suicide attempts

Primary data are new data collected by or for the

investigator

Secondary data refer to existing data

Stages of Development of Information

1) Public health surveillance – development and refinement of data systems for the ongoing and systematic collection, analysis, interpretation and dissemination of information

Stages of Development of Information

2) Risk group identification – identification of persons at greatest risk of disease or injury and the places, times, and other circumstances that are associated with elevated risks

Stages of Development of Information

3) Risk factor identification – analytic exploration of potentially causative risk factors for disease, injury or death as suggested by the high risk population and other research

Stages of Development of Information

4) Program development, implementation, and evaluation – design, implementation and evaluation of preventive interventions based on degree of understanding of the population-at-risk and the risk factors for the outcome of interest

A Caveat on Data Quality(“garbage in - garbage out”)

The government is very keen on amassing statistics. They collect them, add them,

raise them to the nth power, take the cube root and prepare wonderful diagrams. But

you must never forget that every one of these figures comes in the first instance from the village watchman, who just puts

down what he damn well pleases.

Sir Josiah Stamp, British

Economist (1880-1941)