Epidemiology Key Terms

1
EpidemiologyKey Terms Measures

• Fran C. Wheeler, Ph.D
• School of Public Health
• University of South Carolina
• Columbia, SC 29208
• [phone]
• Fran.wheeler_at_sc.edu

2
Developed as part of an Enhanced AHEC Community
Partnership for Health Professions Workforce and
Educational Reform project funded by the Health
Resource and Service Administration (HRSA)
3
OBJECTIVES

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

4
Epidemiology

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

5
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

6
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

7
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

8
Three Essential Components

• Disease distribution
• Disease determinants
• Disease frequency

• Expected level
• Endemic
• Sporadic
• Epidemic
• Pandemic

9
Epidemiologic Studies

• Descriptive
• Analytic

10
Descriptive Studies

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

11
Analytic Studies

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

12
Case Control Study
Exposure
Disease
?
?
Key Basis for selection of group for study
present absent
13
Prospective Cohort Study
Exposure
Disease
?
?
Key Basis for selection of group for
study present absent
14
Retrospective Cohort Study
Exposure
Disease
?
?
Key Basis of selection of group for
study present absent
15
Analytic Studies

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

16
Basic Presentation of Results
All rates and ratios discussed can be calculated
from this
17
Smokingand Carcinoma of the Lung
18
Interpreting Results Measurement Errors

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

19
Interpreting Results Cause-Effect Relationship

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

20
Measures of Disease Frequency

• Prevalence
• Incidence

21
Prevalence

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

22
Types of Prevalence Measures
23
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

24
Types of Incidence Measures
25
Rates Commonly Used in Epidemiology

• Crude
• Category specific
• Age adjusted