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Epidemiology
Epidemiology
Improve health of populations
frequencies of diseases & health states (trends)
factors that causepredicting occurrence & distributionfactors that prevent, prolong life,
improve health
Epidemiology
Identify / Explain causal factors (exposures)
epidemics
epi - above/arounddem - people
Epidemiology
Distribution and determinants
disease, injury, or dysfunction
Epidemiology
Exposures risk (causal) factors
lifestyleoccupational hazardsenvironmental influencesinterventions
Epidemiology
Descriptivedistributions / patterns
Analyticcause and effectmake inferences
Epidemiology
DescriptiveDescriptive ExploratoryExploratory ExperimentalExperimental
DescribePopulations
IdentifyRelationships
Cause and Effect
Clinical TrialsClinical Trials
Cohort/Case-ControlCohort/Case-ControlStudiesStudies
Descriptive Epidemiology
Who
Where
When
Descriptive Epidemiology - Research Designs
Case report/series
Correlational studies
Cross-sectional surveys
NO Causality
Measures of Disease Frequency
Prevalence
Point Prevalence
# of existing cases
total population at risk
Point Prevalence
1,000 therapists in NYS during 1999 had LBP10,000 therapists in NYS
P = 1000/10,000 = 10%
Measures of Disease Frequency
IncidenceCumulative Incidence
# of new cases
total population at risk
Cumulative Incidence
500 therapists in NYS developed LBP in 199910,000 total therapists
CI = 500/10,000 = 5%
Measures of Disease Frequency
Incidence Rate
# of new cases
total person-time
Incident Rate
Of the 10,000 therapists in 1999 - 2,000 worked for only six months8,000 therapists contributed 8,000 person-years2,000 therapists contributed 1,000 person-yearsIR = 500/9,000 = 5.6%
Descriptive EpidemiologyVital Statistics
Birth rateMortality rate:
total mortality - all causes
crude mortality - total mortality / avg. midyear population
Descriptive EpidemiologyVital Statistics
Mortality rate“cause-specific” - specific disease /
avg. midyear population (AIDS, CAD, etc.)
“case-fatality” - deaths / individuals with disease
Age-specific rates
Analytic EpidemiologyObservational Studies Case-Control CohortClinical Trials Intervention Study
DescriptiveDescriptive ExploratoryExploratory ExperimentalExperimental
IdentifyRelationships
Cause and Effect
Clinical TrialsClinical Trials
Cohort/Case-ControlCohort/Case-ControlStudiesStudies
Observational Analytic Designs
Objective:Test hypotheses about
association/relationship of risk factors and disease
Case-Control Studies
Case DefinitionCase Selectionpopulation-based – general
population of those w/ disorder
hospital-based – patients in medical institution
Case-Control Studies
Analysis IssuesSelection bias
Misclassified
Observation/Interviewer bias
Extraneous variables
Cohort (follow-up) Studies
Cohort – group of individuals followed over time
Temporal component
Limited use w/ rare disorders
Cohort Studies
ProspectiveControl and monitor data collectionSubjects readily availableRetrospectiveInexpensive and fasterIncomplete/inadequate data
Cohort Studies
representative sample generalize
group identification
internal comparison
external comparison
Cohort Studies
Analysis Issues
Misclassification -
Attrition -
Clinical Trials (RCT)
Intervention Study
Causality
Rigorous - Gold standard
Prospective - intervention vs. control
Clinical Trials
TherapeuticEffect of rx or intervention
PreventativeAgent/procedure reduce risk of
developing a disease
Clinical Trials
Subject SelectionTarget/Reference
Experimental/accessible population
Clinical Trials
Validitysample size
achievable
attrition
Clinical Trials
Analysisrandomizationblindingbiasethics
Clinical Trials
Analysistests of statistical significance
(difference)t-tests, ANOVA, etc.causalityinferences about the population
Measures of Association - Observational Studies
Test Hypotheses
Relationships
Association Exposure represents a risk factor
Measures of Association
Relative EffectExposed:Unexposed
Absolute EffectDisease Rateexposed - Disease
Rateunexposed
Relative Risk
a bc d
DiseaseYes No
Exp
osur
e
Yes
No
a + b
c + d
a + c b + d N
Relative Risk
Cumulative Incidence Estimate Exposed (CIE)
Unexposed (CIO)
RR = CIE
CIO
= a / (a + b)
c / (c + d)
Relative Risk
50 3319 259
Disease
Yes No
Exp
osur
e Yes
No
a + bc + d
a + c b + d N
Relative Risk
CIE = 50/83 = 0.602
CIO = 19/278 = 0.068
RR = 0.602/0.068 = 8.9
RR = CIE
CIO
= a / (a + b)
c / (c + d)
Relative Risk
Odds Ratio – Case-control
OR = a / cb / d
=adbc
= (50)(259) / (33)(19)
= 20.6
Attributable Risk
Risk Difference = AR = IE - EO
AR = a
a + b - cc+ d
CIE - CIO =
AR = 0.602 - 0.068 = 0.534
AR = 534/1,000
Attributable Proportion
AR% = ARIE
x 100IE -IO
IE
x 100=
AR% =0.534/(50/83) = 88.7%
Attributable Proportion
AR% = OR-1OR
x 100
AR% = 19.6/20.6 = 95.1%
For case-control (Odds Ratio)
Confounding
Extraneous (interfering) variable
associated w/ exposureconsidered a risk factor -
independently of the exposureNOT part of the causal link
Causality
Inherent to interventional research but not observation research subject to interpretation:
Time sequenceStrength of associationBiologic credibilityConsistencyDose-Response
Other Research Approaches
Historical
Evaluation
Methodological
Secondary Analysis
Historical Research
To determine:
how present conditions evolved
anticipate future events
Historical Research
Incorporates:judgementsanalysesinferencesEstablish relationships thru:organizingsynthesizing
Historical Research
Critical Review of:eventsdocumentsliteratureother
Sources of Historical Data
Primaryoriginal documents
letters, videotapes, photographs, minutes
eyewitness accounts
Sources of Historical Data
Secondarybiographiestextbooksencyclopediasliterature reviewsnewspapersummaries
Historical Research
Reliability and Validity
External Criticism authenticity
Internal Criticism content within context of question
Historical Research
After data is collected:
establish relationships
no cause and effect
Evaluation Research
Systematic approach to evaluating programs
clinicalacademic
Effectiveness
Evaluation Research
Establish questions/hypotheses
Choosing variables sensitive
Methodology and design
Evaluation Research
Data Collection and analysis
EvaluationsFormative – performed as part of
program planning or during implementation
Summative – assesses outcomes after program is implemented
Evaluation Research
Evaluation of Program Objectives (measurable)
Quantitative
Qualitative/Behavioral
Evaluation Research
Goal-Free Evaluation
evaluating predetermined goals vs.overall effect of program
Evaluation Research
LimitationsBiasComplexLong termUsefulness
Methodological Research
Development and testing of new instruments/measurement tools
Reliability and Validity applications to various patient populations sensitivity conditions “gold standard”
Methodological Research
Only the beginning
Secondary Analysis
Analyzing previously collected data
subsets of original datanew statistical techniquestest different hypotheses
Secondary Analysis
Advantages:Low costLittle wait for dataLearn from predecessorsDisadvantages:Lack of control of data collection