Epidemiology

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Epidemiology
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Epidemiology

• Improve health of populations
• frequencies of diseases health states (trends)
• factors that cause
• predicting occurrence distribution
• factors that prevent, prolong life, improve health

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Epidemiology

• Identify / Explain causal factors (exposures)
• epidemics
• epi - above/around
• dem - people

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Epidemiology

• Distribution and determinants
• disease, injury, or dysfunction

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Epidemiology

• Exposures ? risk (causal) factors
• lifestyle
• occupational hazards
• environmental influences
• interventions

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Epidemiology

• Descriptive
• distributions / patterns
• Analytic
• cause and effect
• make inferences

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Epidemiology
Exploratory
Experimental
Descriptive
Cause and Effect
Describe Populations
Identify Relationships
Clinical Trials
Cohort/Case-Control Studies
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Descriptive Epidemiology

• Who
• Where
• When

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Descriptive Epidemiology - Research Designs

• Case report/series
• Correlational studies
• Cross-sectional surveys
• NO Causality

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Measures of Disease Frequency

• Prevalence
• Point Prevalence

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Point Prevalence

• 1,000 therapists in NYS during 1999 had LBP
• 10,000 therapists in NYS
• P 1000/10,000 10

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Measures of Disease Frequency

• Incidence
• Cumulative Incidence

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Cumulative Incidence

• 500 therapists in NYS developed LBP in 1999
• 10,000 total therapists
• CI 500/10,000 5

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Measures of Disease Frequency

• Incidence Rate

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Incident Rate

• Of the 10,000 therapists in 1999 - 2,000 worked
  for only six months
• 8,000 therapists contributed 8,000 person-years
• 2,000 therapists contributed 1,000 person-years
• IR 500/9,000 5.6

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Descriptive EpidemiologyVital Statistics

• Birth rate
• Mortality rate
• total mortality - all causes
• crude mortality - total mortality / avg. midyear
  population

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Descriptive EpidemiologyVital Statistics

• Mortality rate
• cause-specific - specific disease / avg.
  midyear population (AIDS, CAD, etc.)
• case-fatality - deaths / individuals with
  disease
• Age-specific rates

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Analytic Epidemiology

• Observational Studies
• Case-Control
• Cohort
• Clinical Trials
• Intervention Study

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Observational Analytic Designs

• Objective
• Test hypotheses about association/relationship of
  risk factors and disease

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Case-Control Studies

• Case Definition
• Case Selection
• population-based general population of those w/
  disorder
• hospital-based patients in medical institution

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Case-Control Studies

• Analysis Issues
• Selection bias
• Misclassified
• Observation/Interviewer bias
• Extraneous variables

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Cohort (follow-up) Studies

• Cohort group of individuals followed over time
• Temporal component
• Limited use w/ rare disorders

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Cohort Studies

• Prospective
• Control and monitor data collection
• Subjects readily available
• Retrospective
• Inexpensive and faster
• Incomplete/inadequate data

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Cohort Studies

• representative sample ? generalize
• group identification
• internal comparison
• external comparison

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Cohort Studies

• Analysis Issues
• Misclassification -
• Attrition -

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Clinical Trials (RCT)

• Intervention Study
• Causality
• Rigorous - Gold standard
• Prospective - intervention vs. control

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Clinical Trials

• Therapeutic
• Effect of rx or intervention
• Preventative
• Agent/procedure reduce risk of developing a
  disease

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Clinical Trials

• Subject Selection
• Target/Reference
• Experimental/accessible population

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Clinical Trials

• Validity
• sample size
• achievable
• attrition

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Clinical Trials

• Analysis
• randomization
• blinding
• bias
• ethics

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Clinical Trials

• Analysis
• tests of statistical significance (difference)
• t-tests, ANOVA, etc.
• causality
• inferences about the population

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Measures of Association - Observational Studies

• Test Hypotheses
• Relationships
• Association ? Exposure represents a risk factor

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Measures of Association

• Relative Effect
• ExposedUnexposed
• Absolute Effect
• Disease Rateexposed - Disease Rateunexposed

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Relative Risk
Disease
No
Yes
a b
Yes
Exposure
No
c d
N
b d
a c
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Relative Risk

• Cumulative Incidence Estimate Exposed (CIE)
• Unexposed (CIO)

RR
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Relative Risk
Disease
Yes
No
Yes
a b
c d
No
Exposure
a c
b d
N
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Relative Risk
RR

• CIE 50/83 0.602
• CIO 19/278 0.068
• RR 0.602/0.068 8.9

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Relative Risk

• Odds Ratio Case-control

OR
(50)(259) / (33)(19) 20.6
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Attributable Risk

• Risk Difference AR IE - EO

AR
CIE - CIO
AR 0.602 - 0.068 0.534 AR 534/1,000
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Attributable Proportion
AR
AR 0.534/(50/83) 88.7
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Attributable Proportion
For case-control (Odds Ratio)
AR
AR 19.6/20.6 95.1
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Confounding

• Extraneous (interfering) variable
• associated w/ exposure
• considered a risk factor - independently of the
  exposure
• NOT part of the causal link

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Causality

• Inherent to interventional research but not
  observation research ? subject to interpretation
• Time sequence
• Strength of association
• Biologic credibility
• Consistency
• Dose-Response

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Other Research Approaches

• Historical
• Evaluation
• Methodological
• Secondary Analysis

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Historical Research

• To determine
• how present conditions evolved
• anticipate future events

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Historical Research

• Incorporates
• judgements
• analyses
• inferences
• Establish relationships thru
• organizing
• synthesizing

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Historical Research

• Critical Review of
• events
• documents
• literature
• other

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Sources of Historical Data

• Primary
• original documents
• letters, videotapes, photographs, minutes
• eyewitness accounts

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Sources of Historical Data

• Secondary
• biographies
• textbooks
• encyclopedias
• literature reviews
• newspaper
• summaries

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Historical Research

• Reliability and Validity
• External Criticism
• authenticity
• Internal Criticism
• content within context of question

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Historical Research

• After data is collected
• establish relationships
• no cause and effect

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Evaluation Research

• Systematic approach to evaluating programs
• clinical
• academic
• Effectiveness

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Evaluation Research

• Establish questions/hypotheses
• Choosing variables
• sensitive
• Methodology and design

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Evaluation Research

• Data Collection and analysis
• Evaluations
• Formative performed as part of program planning
  or during implementation
• Summative assesses outcomes after program is
  implemented

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Evaluation Research

• Evaluation of Program Objectives (measurable)
• Quantitative
• Qualitative/Behavioral

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Evaluation Research

• Goal-Free Evaluation
• evaluating predetermined goals vs.
• overall effect of program

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Evaluation Research

• Limitations
• Bias
• Complex
• Long term
• Usefulness

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Methodological Research

• Development and testing of new instruments/measure
  ment tools
• Reliability and Validity
• applications to various patient populations
• sensitivity
• conditions
• gold standard

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Methodological Research

• Only the beginning

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Secondary Analysis

• Analyzing previously collected data
• subsets of original data
• new statistical techniques
• test different hypotheses

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Secondary Analysis

• Advantages
• Low cost
• Little wait for data
• Learn from predecessors
• Disadvantages
• Lack of control of data collection