Population Health for Health Professionals

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Population HealthforHealth Professionals
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Module 2

• Epidemiology
• The Basic Science
• of Public Health

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OBJECTIVES

• epidemiology and role as foundation for public
  health
• common measures of disease frequency
• strengths and weaknesses of study designs
• applications of epidemiologic method

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Part I

• Key Terms and Measures

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Epidemiology

• Study of distribution of determinants and
  antecedents of health and disease in human
  populations
• Application of results to control of health
  problems

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From Hippocratesto John Graunt

• Fifth century BCE, Hippocrates pointed to the
  need to understand the environment and the risks
  it posed to understand the experience of disease
• 1662, John Graunt analyzed weekly reports of
  births and deaths in London, quantifying patterns
  of disease in the population

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From William Farrto John Snow

• 200 years later, Dr. William Farr was made
  responsible for medical statistics in the Office
  of the Registrar General for England and Wales
• A mere 20 years later, John Snow completed his
  study of cholera

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Modern Experiences

• Evaluation of risk factors for chronic diseases
  using case controls
• Long term population studies using cohorts
• Design of clinical trials to evaluate
  interventions

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Three Essential Components

• Disease distribution
• Disease determinants
• Disease frequency

• Expected level
• Endemic
• Sporadic
• Epidemic
• Pandemic

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Epidemiologic Studies

• Descriptive
• Analytic

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Descriptive Studies

• Frequency of occurrence of particular condition
• Patterns of occurrence according to person, place
  and time

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Analytic Studies

• Observational studies
• case-control studies
• cohort studies
• prospective
• retrospective
• Experimental studies

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Case Control Study
Exposure
Disease
?
?
Key Basis for selection of group for study
present absent
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Prospective Cohort Study
Exposure
Disease
?
?
Key Basis for selection of group for
study present absent
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Retrospective Cohort Study
Exposure
Disease
?
?
Key Basis of selection of group for
study present absent
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Analytic Studies

• Observational studies
• Experimental studies
• Intervention studies
• Clinical trials

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Basic Presentation of Results
All rates and ratios discussed can be calculated
from this.
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Smokingand Carcinoma of the Lung
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Interpreting Results Measurement Errors

• Bias
• information
• selection
• Confounding
• extraneous factors
• Effect modification
• statistical interaction

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Interpreting Results Cause-Effect Relationship

• Strength of the association
• Consistency
• Temporality
• Plausibility
• Biological gradient

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Measures of Disease Frequency

• Prevalence
• Incidence

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Prevalence

• Prevalence number of existing cases divided by
  total population
• Visual examination survey
• 310 X 100 12.5
• 2477

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Types of Prevalence Measures
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Incidence

• Incidence number of new cases in a given period
  of time divided by the total population at risk
• Bacteremia among contraceptive users
• 27/483 X 100 5.6

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Types of Incidence Measures
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Rates Commonly Used in Epidemiology

• Crude
• Category specific
• Age adjusted

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Module Author
Fran C. Wheeler, Ph.D School of Public
Health University of South Carolina