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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)