Epidemiology Introduction Introduction Types of Studies Types of Studies.

EpidemiologyEpidemiology

IntroductionIntroduction Types of StudiesTypes of Studies

Definition of EpidemiologyDefinition of Epidemiology

RecallRecall

– Epidemiology literally means “the study of what is Epidemiology literally means “the study of what is upon the people.” It puts the individual's condition upon the people.” It puts the individual's condition in a population context and is the path to disease in a population context and is the path to disease prevention. prevention.

Key wordsKey words

StudyStudy DistributionDistribution DeterminantsDeterminants Health-related statesHealth-related states PopulationsPopulations ControlControl

Epidemiology key words:Epidemiology key words:

StudyStudy

– Epidemiology is the basic science of public health.Epidemiology is the basic science of public health.

– It's a highly quantitative discipline based on It's a highly quantitative discipline based on principles of statistics and research principles of statistics and research methodologies.methodologies.


DistributionDistribution– Epidemiologists study the distribution of Epidemiologists study the distribution of

frequencies and patterns of health events within frequencies and patterns of health events within groups in a population.groups in a population.

– They use descriptive epidemiology, which They use descriptive epidemiology, which characterizes health events in terms of time, characterizes health events in terms of time, place, and person.place, and person.

– – Questions: who, what, where, whenQuestions: who, what, where, when


DeterminantsDeterminants

Epidemiologists also attempt to search for causes or Epidemiologists also attempt to search for causes or factors that are associated with increased risk or factors that are associated with increased risk or probability of disease.probability of disease.

This type of epidemiology is referred to as analytical This type of epidemiology is referred to as analytical epidemiologyepidemiology

» Questions: how and whyQuestions: how and why

Virtual Field TripVirtual Field Trip

http://www.whatispublichealth.org/what/index.htmlhttp://www.whatispublichealth.org/what/index.html

Epidemiologic ProcessEpidemiologic Process

WHO WHO was affected?was affected? WHERE WHERE were they affected?were they affected? WHEN WHEN were they affected?were they affected?

HOWHOW

andand WHYWHY??

Why are the who, when, and where Why are the who, when, and where questions useful in determining questions useful in determining

the causes of disease?the causes of disease?

The epidemiologist attempts to determine who is The epidemiologist attempts to determine who is prone to a particular disease; prone to a particular disease;

where risk of the disease is highest; where risk of the disease is highest; when the disease is most likely to occur and its when the disease is most likely to occur and its

trends over time; trends over time; what exposure its victims have in common;what exposure its victims have in common; how much the risk is increased through exposure; how much the risk is increased through exposure; and how many cases of the disease could be avoided and how many cases of the disease could be avoided

by eliminating the exposure.by eliminating the exposure.

Why are the who, when, and where Why are the who, when, and where questions useful in determining questions useful in determining

the causes of disease?the causes of disease?

The study of the distribution of diseases in The study of the distribution of diseases in populations and of factors that influence the populations and of factors that influence the occurrence of disease. Epidemiology examines occurrence of disease. Epidemiology examines epidemic (excess) and endemic (always present) epidemic (excess) and endemic (always present) diseases; it is based on the observation that most diseases; it is based on the observation that most diseases do not occur randomly, but are related to diseases do not occur randomly, but are related to environmental and personal characteristics that vary environmental and personal characteristics that vary by place, time, and subgroup of the populationby place, time, and subgroup of the populationRead more:

WHO WHO was affected?was affected?PersonPerson

AgeAge SexSex Race/EthnicityRace/Ethnicity Socio-Economic StatusSocio-Economic Status BehaviorsBehaviors

WHERE WHERE were they affected?were they affected?PlacePlace

Geographic DistributionGeographic Distribution– Clustering, uniform, scatteredClustering, uniform, scattered

HomeHome WorkWork SchoolSchool Hospital roomHospital room

Geographic Distribution of Geographic Distribution of LaCrosseLaCrosse

ClusteredClustered

ScatteredScattered

WHEN WHEN were they affected?were they affected?TimeTime

Onset of symptomsOnset of symptoms Incubation PeriodIncubation Period Infectious PeriodInfectious Period SeasonalitySeasonality EpidemicEpidemic IntervalInterval

– Long-term trendsLong-term trends– Shorter for environmental exposureShorter for environmental exposure

Health-related statesHealth-related states

Health-related statesHealth-related states Epidemiology is applied to the whole spectrum of Epidemiology is applied to the whole spectrum of

healthrelated events:healthrelated events:

– – chronic diseases,chronic diseases,

– – environmental problems,environmental problems,

– – behavioral problems,behavioral problems,

– – injuries,injuries,

– – infectious diseases.infectious diseases.


PopulationsPopulations

– One of the most important distinguishing One of the most important distinguishing characteristics of epidemiology is that it deals with characteristics of epidemiology is that it deals with groups of people rather than with individual groups of people rather than with individual patients.patients.


ControlControl Epidemiology can be used simply as an analytical Epidemiology can be used simply as an analytical

tool for studying diseases and their determinants.tool for studying diseases and their determinants. Epidemiological data also steers public health Epidemiological data also steers public health

decision making and aids in developing and decision making and aids in developing and evaluating interventions to control and prevent health evaluating interventions to control and prevent health problems.problems.

How is Epidemiology Used?How is Epidemiology Used?

Population/community health assessmentPopulation/community health assessment– Personal decision-makingPersonal decision-making– Complete clinical pictureComplete clinical picture– Evaluate interventionsEvaluate interventions– Search for causeSearch for cause

» Exposure and relationship to diseaseExposure and relationship to disease» Outbreak investigationOutbreak investigation

Aim of Epidemiological studiesAim of Epidemiological studies

To determine distribution of diseaseTo determine distribution of disease

To examine determinants of a diseaseTo examine determinants of a disease

To judge whether a given exposure causes or To judge whether a given exposure causes or prevents disease.prevents disease.

Establishing a cause-and-effectEstablishing a cause-and-effectrelationship: Five criteriarelationship: Five criteria

Strength of associationStrength of association—the relationship must be —the relationship must be clear.clear.

ConsistencyConsistency—observation of the association must —observation of the association must be repeatable in different populations at different be repeatable in different populations at different times.times.

TemporalityTemporality—the cause must precede the effect.—the cause must precede the effect. PlausibilityPlausibility—the explanation must make sense —the explanation must make sense

biologically.biologically. Biological gradientBiological gradient—there must be a dose-—there must be a dose-

response relationshipresponse relationship

Explain the interaction between Explain the interaction between incidence, prevalenceincidence, prevalence

IncidenceIncidence

Number of new events occurring in a defined Number of new events occurring in a defined population during specific period of time population during specific period of time

» Incidence = New cases/ Pop at risk/timeIncidence = New cases/ Pop at risk/time Used to measure current disease activityUsed to measure current disease activity Allows comparison between areas with different Allows comparison between areas with different

populations.populations.

Contrasts with PrevalenceContrasts with Prevalence

Prevalence =Prevalence =– (new cases + existing cases) / Total Population(new cases + existing cases) / Total Population

» Can be expressed as percentCan be expressed as percent» Can give a picture of disease burden within a Can give a picture of disease burden within a

populationpopulation

What has epidemiology contributed to What has epidemiology contributed to people’s understanding of: people’s understanding of:

• Heart disease?Heart disease?• Decline in CVD Death RatesDecline in CVD Death Rates• Advances in PreventionAdvances in Prevention

• Lung cancer? Lung cancer? • Contemporary epidemiologic research on lung Contemporary epidemiologic research on lung

cancer now focuses on a new set of issues, cancer now focuses on a new set of issues,

Heart DiseaseHeart Disease

established the major risk factors ofestablished the major risk factors of high blood cholesterol,high blood cholesterol, high blood pressure, high blood pressure, and smoking and and smoking and dietary factors (particularly dietary cholesterol, fat, dietary factors (particularly dietary cholesterol, fat,

and sodium). and sodium). The risk factor concept--that particular biologic, The risk factor concept--that particular biologic,

lifestyle, and social conditions were associated with lifestyle, and social conditions were associated with increased risk for diseaseincreased risk for disease

Lung CancerLung Cancer

SmokingSmoking changes in tobacco productschanges in tobacco products Diet Diet Questions have also been raised about possible Questions have also been raised about possible

differences in susceptibility to lung cancer by sex and differences in susceptibility to lung cancer by sex and race.race.

Tuskegee Syphilis Study Tuskegee Syphilis Study

A forty year study of syphilis by the US Government A forty year study of syphilis by the US Government that didn't reveal the disease to those infected. In that didn't reveal the disease to those infected. In 1932 the American Government promised 400 men - 1932 the American Government promised 400 men - all residents of Macon County, Alabama, all poor, all all residents of Macon County, Alabama, all poor, all African American - free treatment for Bad Blood, a African American - free treatment for Bad Blood, a euphemism for syphilis which was epidemic in the euphemism for syphilis which was epidemic in the countycounty

. Treatment for syphilis was never given to the men . Treatment for syphilis was never given to the men and was in fact withheld. The men became unwitting and was in fact withheld. The men became unwitting subjects for a government sanctioned medical subjects for a government sanctioned medical investigation, The Tuskegee Study of Untreated investigation, The Tuskegee Study of Untreated Syphilis in the Negro Male. The Tuskegee Study, Syphilis in the Negro Male. The Tuskegee Study, which lasted for 4 decades, until 1972, had nothing to which lasted for 4 decades, until 1972, had nothing to do with treatment. do with treatment.

No new drugs were tested; neither was any effort No new drugs were tested; neither was any effort made to establish the efficacy of old forms of made to establish the efficacy of old forms of treatment. It was a non therapeutic experiment, treatment. It was a non therapeutic experiment, aimed at compiling data on the effects of the aimed at compiling data on the effects of the spontaneous evolution of syphilis on black males. spontaneous evolution of syphilis on black males.

What has become clear since the story was broken What has become clear since the story was broken by Jean Heller in 1972 was that the Public Health by Jean Heller in 1972 was that the Public Health Service (PHS) was interested in using Macon County Service (PHS) was interested in using Macon County and its black inhabitants as a laboratory for studying and its black inhabitants as a laboratory for studying the long term effects of untreated syphilis, not in the long term effects of untreated syphilis, not in treating this deadly disease.treating this deadly disease.

Why was it unethical? Why was it unethical?

The subjects of the study bear witness to the premise The subjects of the study bear witness to the premise that the burden of medical experimentation has that the burden of medical experimentation has historically been borne by those least able to protect historically been borne by those least able to protect themselves.themselves.

The Tuskegee Study symbolizes the medical The Tuskegee Study symbolizes the medical misconduct and blatant disregard for human rights misconduct and blatant disregard for human rights that takes place in the name of science. The studies that takes place in the name of science. The studies principal investigators were not mad scientists, they principal investigators were not mad scientists, they were government physicians, respected men of were government physicians, respected men of science, who published reports on the study in the science, who published reports on the study in the leading medical journalsleading medical journals

Using Human Beings as Using Human Beings as Laboratory AnimalsLaboratory Animals

What has become clear since the story was broken What has become clear since the story was broken by Jean Heller in 1972 was that the Public Health by Jean Heller in 1972 was that the Public Health Service (PHS) was interested in using Macon County Service (PHS) was interested in using Macon County and its black inhabitants as a laboratory for studying and its black inhabitants as a laboratory for studying the long term effects of untreated syphilis, not in the long term effects of untreated syphilis, not in treating this deadly disease. treating this deadly disease.

Daily Ethical Encounters

Participants who are vulnerable Participants who are vulnerable from:from:

Abuse from Doctor-patient Abuse from Doctor-patient relationshiprelationship

““whatever you say, doc” syndromewhatever you say, doc” syndrome

Indigent patientsIndigent patients

Daily Ethical Encounters

Financial Pressures and Conflict of Financial Pressures and Conflict of InterestInterest FinancialFinancial

Income for DepartmentIncome for Department BonusesBonuses Structure of grant (pay per visit or end-loaded)Structure of grant (pay per visit or end-loaded) Pay for screeningPay for screening Pay for quality of data, rather than # of patientsPay for quality of data, rather than # of patients Avoid disincentives for dropping a patient (e.g., Avoid disincentives for dropping a patient (e.g.,

due to adverse reactiondue to adverse reaction Pressure re prestiege, publication, tenurePressure re prestiege, publication, tenure

Tuskegee Syphilis StudyTuskegee Syphilis Study

What influence has it had on the conduct of clinical What influence has it had on the conduct of clinical trials? , and prognosis. trials? , and prognosis.

1932–72 Tuskegee experiment on syphilis1939–45 Nazi experiments1944–74 Human radiation experiments by U.S. government1946 Nuremberg Trial of doctors responsible for the Nazi experiments1947 Nuremberg Code outlining ethical principles required for research1948 United Nations adoption of Universal Declaration of Human Rights

Milestones in Ethical Milestones in Ethical DevelopmentDevelopment


1953 NIH policy, the first U.S. federal policy introducing independent reviewers to

examine research, forerunners of the IRBs 1963–66 Willowbrook Study, involving hepatitis

research on mentally retarded children, raising issues access to care, consent, and coercion 1964 Declaration of Helsinki international

agreement on recommendations for the ethical conduct of medical research 1972 Public exposure of Tuskegee syphilis study 1974 First federal protections for human research

participants


1979 Belmont Report promoting three principles for research

1980 Food and Drug Administration regulations (CFR 21 (50)

1982 Council for the International Organization of Medical Sciences (CIOMS) publication of the International Ethics Guidelines for Biomedical Research Involving Human Subjects

1985 U.S. Public Health Service Task Force on Women’s Health issues report encouraging inclusion of women in research

1990 Society for Women’s Health Research


1993 Public exposure of U.S. human radiation experiments

1993 NIH Revitalization Act mandating inclusion of women and minorities in research

1993 NIH Office of Research on Women’s Health


1997 Food and Drug Modernization Act (FDAMA) requiring the FDA, NIH, and pharmaceutical industry to develop guidance on the inclusion of women and minorities in trials

1998 Pediatric Rule passed by Congress, stipulating that new drugs for children must include specific pediatric labeling information

2000 Further publicized ethical abuses prompting establishment of the Office of Human Research Protections (OHRP)

Belmont ReportBelmont Report

National Commission for the Protection of Human Subjects of Biomedical and Behavioral Research

3 basic principles for research


Respect for persons, or an individual’s autonomy-

elements of the informed consent requiring that: Information necessary to make a decision must

be presented that is,the risks and benefits, if any, of participation.

The information must be presented at a level that can be understood by the patient or study subject.

Participation must be voluntary.


Benificience, or benefit to the Benificience, or benefit to the participantparticipant

Who decides whether there is Who decides whether there is benefit?benefit?

Belmont-BeneficenceBelmont-Beneficence

Loss of substantial benefits that might be gained from research

PaternalismPregnancyLife-threatening illness

(AIDS/Cancer)

Belmont-JusticeBelmont-Justice

Risks and benefits should be Risks and benefits should be equitably distributed among different populations “Do onto others…” rather than taking

advantage of

Vulnerable populations

Vulnerable Populations

Military Military 1944-1979: radiation, chemical,1944-1979: radiation, chemical,

Mustard gas, lewisiteMustard gas, lewisite Venezuelan equine encephalitis virus and the nervegas agent VX Operation Whitecoat (tularemia, anthrax, Q fever)

1994 Congressional review: the Department of Defense

“has demonstrated a pattern of misrepresenting the danger of various military exposures that continues today”

Vulnerable Populations

Unsuspecting civiliansUnsuspecting civilians Radiation experiments: atomic weapons Radiation experiments: atomic weapons

testing intesting in South PacificSouth Pacific Oak RidgeOak Ridge Los AlamosLos Alamos Hanford, WashingtonHanford, Washington Plutoniaum injections (ACHRE report)Plutoniaum injections (ACHRE report)

Vulnerable PopulationsVulnerable Populations

What studies are being done now under the guise of counter terrorism, hidden from the public by the “Patriot Act?”

Vulnerable Populations-Children

Pint-size people vs. real dataPint-size people vs. real data 10 drugs most commonly prescribed for

children that lacked pediatric labeling—drugs were prescribed more than 5 million times

HIV studies in foster children Too vulnerable? vs denying access to Too vulnerable? vs denying access to

potentially life-saving drugspotentially life-saving drugs (all HIV + kids were being offered the trials)(all HIV + kids were being offered the trials)

Vulnerable Populations-Women

PregnancyPregnancy PaternalismPaternalism Woman vs FetusWoman vs Fetus

Explain the three major types of Explain the three major types of epidemiologic studies.epidemiologic studies.

Qualitative Qualitative QuantitativeQuantitative

–ExperimentalExperimental–ObservationalObservational

»BasicBasic»HybridHybrid»IncompleteIncomplete

Comparison (I)Comparison (I)

QualitativeQualitative UnderstandingUnderstanding Interview/observationInterview/observation Discovering frameworksDiscovering frameworks Textual (words)Textual (words) Theory generatingTheory generating Quality of informant more important Quality of informant more important

than sample sizethan sample size SubjectiveSubjective Embedded knowledgeEmbedded knowledge Models of analysis: fidelity to text or Models of analysis: fidelity to text or

words of intervieweeswords of interviewees

QuantitativeQuantitative PredictionPrediction Survey/questionnairesSurvey/questionnaires Existing frameworksExisting frameworks NumericalNumerical Theory testing (experimental)Theory testing (experimental) Sample size core issue in reliability of Sample size core issue in reliability of

data data ObjectiveObjective PublicPublic Model of analysis:parametric, non-Model of analysis:parametric, non-

parametricparametric

Comparison (II)Comparison (II)

QuantitativeQuantitative MethodsMethods

– ObservationalObservational– ExperimentalExperimental– Mixed Mixed – SamplingSampling: Random : Random

(simple, stratified, cluster, (simple, stratified, cluster, etc) or purposive etc) or purposive

Quality AssuranceQuality Assurance::– Reliability:Reliability: Internal and Internal and

ExternalExternal– ValidityValidity: Construct, : Construct,

Content, Face Content, Face

QualitativeQualitative MethodsMethods

– Focus Groups Focus Groups – InterviewsInterviews– Surveys Surveys – Self-reports Self-reports – Observations Observations – Document analysisDocument analysis– SamplingSampling: Purposive: Purposive

Quality Assurance:Quality Assurance:– TrustworthinessTrustworthiness: Credibility, : Credibility,

Confirmability, Dependability, Confirmability, Dependability, Transferability Transferability

– Authenticity:Authenticity: Fairness, Fairness, Ontological, Educative, Ontological, Educative, Tactical, Catalytic Tactical, Catalytic

Qualitative Research TechniquesQualitative Research Techniques

Participant observation (field notes)Participant observation (field notes) Interviews / Focus group discussions Interviews / Focus group discussions

with key infomantswith key infomants Video / Text and Image analysis Video / Text and Image analysis

(documents, media data)(documents, media data) SurveysSurveys User testingUser testing

Involves Skills ofInvolves Skills of

ObservingObserving

ConversingConversing

ParticipatingParticipating

InterpretingInterpreting

Qualitative Techniques (I)Qualitative Techniques (I)

Participant observation Participant observation – Gains insight into understanding cultural patterns to Gains insight into understanding cultural patterns to

determine what’s necessary and needed in tool determine what’s necessary and needed in tool development (complementary to interviews)development (complementary to interviews)

Interviews/Focus groups with stakeholdersInterviews/Focus groups with stakeholders– Explores how tools are used and could be used in a novice Explores how tools are used and could be used in a novice

programming courseprogramming course– Gains insight into the meaning of tools for students for Gains insight into the meaning of tools for students for

learning to programlearning to program

Qualitative Techniques: (II)Qualitative Techniques: (II)

Data analysisData analysis– Themes arising from data would provide insight into current Themes arising from data would provide insight into current

“learning to program” issues and see what is important to “learning to program” issues and see what is important to students / teachers / administrators students / teachers / administrators

Survey Survey – Useful for verifying results on a larger scaleUseful for verifying results on a larger scale

User TestingUser Testing– Useful for triangulating results Useful for triangulating results

Rigor in Qualitative ResearchRigor in Qualitative Research

DependabilitDependabilityy

CredibilityCredibility TransferabilitTransferabilit

yy ConfirmabilitConfirmabilit

yy

Quantitative DesignsQuantitative Designs

Quantitative designsQuantitative designs

ObservationalObservational: studies that do not : studies that do not involve any intervention or involve any intervention or experiment. experiment.

ExperimentalExperimental: studies that entail : studies that entail manipulationmanipulation of the study factor of the study factor (exposure) and (exposure) and randomizationrandomization of of subjects to treatment (exposure) subjects to treatment (exposure) groupsgroups

Observational DesignsObservational Designs

Observation MethodsObservation Methods

Selected UnitsSelected Units: individuals, groups : individuals, groups Study PopulationsStudy Populations: cross-sectional, : cross-sectional,

longitudinal longitudinal Data collection timingData collection timing: prospectively, : prospectively,

retrospectively, combinationretrospectively, combination Data collection typesData collection types: primary, : primary,

secondarysecondary

Study populationsStudy populations

Cross-sectionalCross-sectional:: where only where only ONEONE set of set of observations is collected for every unit in the study, at observations is collected for every unit in the study, at a certain point in time, disregarding the length of time a certain point in time, disregarding the length of time of the study as a wholeof the study as a whole

LongitudinalLongitudinal:: where where TWO or MORETWO or MORE sets of sets of observations are collected for every unit in the study, observations are collected for every unit in the study, i.e. follow-up is involved in order to allow monitoring i.e. follow-up is involved in order to allow monitoring of a certain population (cohort) over a specified of a certain population (cohort) over a specified period of time. Such populations are AT RISK period of time. Such populations are AT RISK (disease-free) at the start of the study.(disease-free) at the start of the study.

Observational Designs Observational Designs (Classification I)(Classification I)

ExploratoryExploratory: used when the state of : used when the state of knowledge about the phenomenon is poor: knowledge about the phenomenon is poor: small scale; of limited duration.small scale; of limited duration.

DescriptiveDescriptive: used to formulate a certain : used to formulate a certain hypothesis: small / large scale. Examples: hypothesis: small / large scale. Examples: case-studies; cross-sectional studies case-studies; cross-sectional studies

AnalyticalAnalytical: used to test hypotheses: small / : used to test hypotheses: small / large scale. Examples: case-control, cross-large scale. Examples: case-control, cross-sectional, cohortsectional, cohort..

Observational DesignsObservational Designs (Classification II) (Classification II)

PreliminaryPreliminary (case-reports, case-series) (case-reports, case-series) Basic Basic (cross-sectional, case-control, (cross-sectional, case-control,

cohort [prospective, retrospective] )cohort [prospective, retrospective] ) HybridHybrid (two or more of the above, (two or more of the above,

nested case-control within cohort, etc)nested case-control within cohort, etc) IncompleteIncomplete (ecological, PMR, etc) (ecological, PMR, etc) OthersOthers (repeated, case cross-over, (repeated, case cross-over,

migrant, twin, etc)migrant, twin, etc)

Case-series: Case-series: Clinical case seriesClinical case series

Clinical case-series:Clinical case-series: usually a coherent and usually a coherent and consecutive set of cases of a disease (or similar consecutive set of cases of a disease (or similar problem) which derive from either the practice of problem) which derive from either the practice of one or more health care professionals or a defined one or more health care professionals or a defined health care setting, e.g. a hospital or family practice. health care setting, e.g. a hospital or family practice.

A case-series is, effectively, a A case-series is, effectively, a registerregister of cases. of cases. Analyse cases together to learn about the diseaseAnalyse cases together to learn about the disease. . Clinical case-series are of value in epidemiology for:Clinical case-series are of value in epidemiology for:

– Studying symptoms and signs Studying symptoms and signs – Creating case definitions Creating case definitions – Clinical education, audit and research Clinical education, audit and research

Case series: Case series: PPopulation basedopulation based

When a When a clinical case-seriesclinical case-series is complete is complete for a defined geographical area for which for a defined geographical area for which the population is known, it is, effectively, the population is known, it is, effectively, a a population based case-seriespopulation based case-series consisting consisting of a population register of cases. of a population register of cases.

Epidemiologically the most important Epidemiologically the most important case-series are registers of serious case-series are registers of serious diseases or deaths (usually NCDs), and of diseases or deaths (usually NCDs), and of health service utilisation, e.g. hospital health service utilisation, e.g. hospital admissions. admissions.

Usually compiled for administrative and Usually compiled for administrative and legal reasons. legal reasons.

Case series: Case series: Natural history and spectrumNatural history and spectrum

By delving into the past circumstances of By delving into the past circumstances of these patients, including examination of these patients, including examination of past medical records, and by continuing past medical records, and by continuing to observe them to death (and necropsy to observe them to death (and necropsy as appropriate), health professionals can as appropriate), health professionals can build up a picture of the build up a picture of the natural history natural history of a diseaseof a disease. .

Population case-series is a systematic Population case-series is a systematic extension of this series but which extension of this series but which includes additional cases, e.g. those includes additional cases, e.g. those dying without being seen by the dying without being seen by the clinicians. clinicians.

Add breadth to the understanding of the Add breadth to the understanding of the spectrum and natural history of disease. spectrum and natural history of disease.

Case series: PopulationCase series: Population

Full epidemiological use of case-series data Full epidemiological use of case-series data needs information on the population to needs information on the population to permit calculation of permit calculation of ratesrates

Key to understanding the distribution of Key to understanding the distribution of disease in populations and to the study of disease in populations and to the study of variations over time, between places and by variations over time, between places and by population characteristics population characteristics

Case-series Case-series can provide the key to sound can provide the key to sound case control and cohort studies and trialscase control and cohort studies and trials

Design of a case-series is conceptually simpleDesign of a case-series is conceptually simple Defines a disease or health problem to be Defines a disease or health problem to be

studied and sets up a studied and sets up a system for capturing system for capturing data on the health status and related factors data on the health status and related factors in consecutive cases in consecutive cases

Case series: Case series: Requirements for interpretationRequirements for interpretation

To make sense of case-series data the key To make sense of case-series data the key requirements are:requirements are:

The diagnosis (case definition) or, for mortality, the The diagnosis (case definition) or, for mortality, the cause of deathcause of death

The date when the disease or death occurred The date when the disease or death occurred (time)(time) The place where the person lived, worked etc The place where the person lived, worked etc (place)(place) The characteristics of the person The characteristics of the person (person)(person) The opportunity to collect additional data from The opportunity to collect additional data from

medical records (possibly by electronic data linkage) medical records (possibly by electronic data linkage) or the person directlyor the person directly

The size and characteristics of the The size and characteristics of the population at riskpopulation at risk

Case series: Additional dataCase series: Additional data

Case-series data can be Case-series data can be linked to other health datalinked to other health data either in the past or the future, e.g. mortality data either in the past or the future, e.g. mortality data can be linked to hospital admissions including at can be linked to hospital admissions including at birth and childhood, cancer registrations and other birth and childhood, cancer registrations and other records to obtain information on exposures and records to obtain information on exposures and disease. disease.

Cases may also be Cases may also be contactedcontacted for additional for additional information. information.

This type of action This type of action may turn a case-series design may turn a case-series design into a cohort designinto a cohort design..

Case series: StrengthsCase series: Strengths

Population case-series permit two arguably Population case-series permit two arguably unique forms of epidemiological analysis unique forms of epidemiological analysis and insight. and insight.

Paint a truly national and even international Paint a truly national and even international population perspective on diseasepopulation perspective on disease. .

The disease patterns can be The disease patterns can be related to related to aspects of society or the environmentaspects of society or the environment that that affect the population but have no sensible affect the population but have no sensible measure at the individual level e.g. ozone measure at the individual level e.g. ozone concentration at ground level and the concentration at ground level and the thickness of the ozone layer in the earth's thickness of the ozone layer in the earth's atmosphere. atmosphere.

Cross-sectional StudiesCross-sectional Studies(Community health studies, surveys) (Community health studies, surveys)

CharacteristicsCharacteristics:: detects point prevalence; relative detects point prevalence; relative conditions; allows for stratificationconditions; allows for stratification

MeritsMerits:: feasible; quick; economic; allows study of feasible; quick; economic; allows study of several diseases / exposures; useful for estimation of several diseases / exposures; useful for estimation of the population burden, health planning and priority the population burden, health planning and priority setting of health problemssetting of health problems

LimitationsLimitations:: temporal ambiguity (cannot determine temporal ambiguity (cannot determine whether the exposure preceded outcome); possible whether the exposure preceded outcome); possible measurement error; not suitable for rare conditions; measurement error; not suitable for rare conditions; liable to survivor biasliable to survivor bias

Effect measure:Effect measure: Odds Ratio Odds Ratio

Case - Control StudiesCase - Control Studies

CharacteristicsCharacteristics: two source populations; assumption : two source populations; assumption that non-cases are representative of the source that non-cases are representative of the source population of cases.population of cases.

MeritsMerits:: least expensive; least time-consuming; least expensive; least time-consuming; suitable for study of rare diseases (especially NCDs)suitable for study of rare diseases (especially NCDs)

LimitationsLimitations: not suitable for rare exposures; liable to : not suitable for rare exposures; liable to selection bias and recall bias; not suitable for selection bias and recall bias; not suitable for calculation of frequency measures.calculation of frequency measures.

Effect measure:Effect measure: Odds Ratio Odds Ratio

Cohort StudiesCohort Studies

CharacteristicsCharacteristics: follow-up period (prospective; : follow-up period (prospective; retrospective) retrospective)

Merits:Merits: no temporal ambiguity; several no temporal ambiguity; several outcomes could be studied at the same time; outcomes could be studied at the same time; suitable for incidence estimationsuitable for incidence estimation

Limitations (of prospective type):Limitations (of prospective type): expensive; expensive; time-consuming; inefficient for rare diseases; time-consuming; inefficient for rare diseases; may not be feasiblemay not be feasible

Effect measure:Effect measure: Risk Ratio (Relative Risk) Risk Ratio (Relative Risk)

Coh

ort D

esig

nC

ohor

t Des

ign

time

Study begins here

Studypopulation

free ofdisease

Factorpresent

Factorabsent

disease

no disease

disease

no disease

presentfuture

Ecological studies (I)Ecological studies (I)

These are studies where exposure data relating These are studies where exposure data relating to a place (say hardness of water, which could be to a place (say hardness of water, which could be collected on individuals) are correlated with collected on individuals) are correlated with health data collected on individuals but health data collected on individuals but summarised by place (say CHD rates). summarised by place (say CHD rates).

Conceptually, the ecological component in this Conceptually, the ecological component in this kind of study is an issue of data analysis and not kind of study is an issue of data analysis and not study designstudy design. .

What is missing: relationship between exposure and What is missing: relationship between exposure and outcome at the individual level (incomplete design)outcome at the individual level (incomplete design)

Ecological studies (II)Ecological studies (II)

Cross-sectional, case-control and cohort studies Cross-sectional, case-control and cohort studies and trials (and not just population case-series) and trials (and not just population case-series) could also be analysed in relation to such could also be analysed in relation to such "ecological" variables and such units of analysis."ecological" variables and such units of analysis.

Most ecological analyses are based on Most ecological analyses are based on population population case-series. case-series.

Ecological analyses are subject to the ecological Ecological analyses are subject to the ecological fallacy.fallacy.

Ecological fallacy: exampleEcological fallacy: example

Imagine a study of the rate of coronary heart disease in the Imagine a study of the rate of coronary heart disease in the capital cities of the world relating the rate to average capital cities of the world relating the rate to average income. income.

Within the cities studied, coronary heart disease is higher in Within the cities studied, coronary heart disease is higher in the richer cities than in the poorer ones. the richer cities than in the poorer ones.

We might predict from such a finding that being rich We might predict from such a finding that being rich increases your risk of heart disease. increases your risk of heart disease.

In the industrialised world the opposite is the case - within In the industrialised world the opposite is the case - within cities such as London, Washington and Stockholm, poor cities such as London, Washington and Stockholm, poor people have higher CHD rates than rich ones. people have higher CHD rates than rich ones.

The ecological fallacy is usually interpreted as a major The ecological fallacy is usually interpreted as a major weakness of ecological analyses. weakness of ecological analyses.

Ecological analyses, however, informs us about forces Ecological analyses, however, informs us about forces which act on whole populations. which act on whole populations.

Experimental DesignsExperimental Designs

Experimental Study DesignExperimental Study Design

A study in which a population is selected A study in which a population is selected for a planned trial of a regimen, whose for a planned trial of a regimen, whose effects are measured by comparing the effects are measured by comparing the outcome of the regimen in the outcome of the regimen in the experimentalexperimental group versus the outcome of group versus the outcome of another regimen in the another regimen in the controlcontrol group. group. Such designs are differentiated from Such designs are differentiated from observational designs by the fact that observational designs by the fact that there is there is manipulation of the studymanipulation of the study factor factor (exposure), and (exposure), and randomization (randomization (random random allocation) of subjects to treatment allocation) of subjects to treatment (exposure) groups. (exposure) groups.

Why Performed ?Why Performed ?

1.1. Provide stronger Provide stronger evidenceevidence of the effect of the effect (outcome) compared to observational designs, (outcome) compared to observational designs, with maximum confidence and assurancewith maximum confidence and assurance

2.2. Yield more Yield more valid resultsvalid results, as variation is , as variation is minimized and bias controlledminimized and bias controlled

3.3. Determine whether experimental treatments Determine whether experimental treatments are safe and effective under are safe and effective under “controlled “controlled environments”environments” (as opposed to “natural (as opposed to “natural settings” in observational designs), especiallysettings” in observational designs), especially

when the margin of expected benefit is doubtful when the margin of expected benefit is doubtful / narrow (10 - 30%)/ narrow (10 - 30%)

Exp

erim

enta

l Des

ign

Exp

erim

enta

l Des

ign

timeStudy begins here (baseline point)

Studypopulation

Intervention

Control

outcome

no outcome

outcome

no outcome

baselinefuture

RANDOMIZATION

Types of trialsTypes of trials

B lind ed N o t b lind ed

R a nd o m ised N o t ran d om ised

C o n tro lled N o t co n tro lled

T ria l

Choice of DesignChoice of Design

• Which is most likely to yield a valid result? Why?

• Which is likely to yield an answer in the shortest period of time? Why?

Choice of Design (I)Choice of Design (I)

Depends on: Depends on:

– Research QuestionsResearch Questions

– Research GoalsResearch Goals

– Researcher Beliefs and ValuesResearcher Beliefs and Values

– Researcher SkillsResearcher Skills

– Time and FundsTime and Funds

Choice of design (II)Choice of design (II)

It is also related to:It is also related to: Status of existent knowledgeStatus of existent knowledge Occurrence of diseaseOccurrence of disease Duration of latent periodDuration of latent period Nature and availability of informationNature and availability of information Available resourcesAvailable resources

Comparing study designsComparing study designs

ThemeTheme EaseEase TimingTiming Maintenance and continuityMaintenance and continuity CostsCosts EthicsEthics Data utilisationData utilisation Main contributionMain contribution Observer biasObserver bias Selection biasSelection bias Analytic output Analytic output

Conclusion (I)Conclusion (I)

Qualitative designs are complementary to Qualitative designs are complementary to quantitative designs, are important in study of social quantitative designs, are important in study of social determinants of health problemsdeterminants of health problems

Quantitative designs have a common goal to Quantitative designs have a common goal to understand the frequency and causes of health-understand the frequency and causes of health-related phenomenarelated phenomena

Seeking causes starts by describing associations Seeking causes starts by describing associations between exposures (causes) and outcomes between exposures (causes) and outcomes

Conclusion (II)Conclusion (II)

Case-series is a coherent set of cases of a disease (or Case-series is a coherent set of cases of a disease (or similar problem). similar problem).

Cases are compared with reference group, we have a Cases are compared with reference group, we have a case control study case control study

In a population studied at a specific time and place (a In a population studied at a specific time and place (a cross-section) the primary output is prevalence data, cross-section) the primary output is prevalence data, though association between risk factors and disease can though association between risk factors and disease can be generated.be generated.

In cross-sectional studies, we are looking for both In cross-sectional studies, we are looking for both exposure and outcomeexposure and outcome

In case-control studies, we know the outcome, looking In case-control studies, we know the outcome, looking for the exposurefor the exposure

In cohort studies, we know the outcome, following up In cohort studies, we know the outcome, following up looking for the outcome in question looking for the outcome in question

Conclusion (III)Conclusion (III)

If the population in a cross-sectional survey is followed up to If the population in a cross-sectional survey is followed up to measure health outcomes, this study design is a cohort study. measure health outcomes, this study design is a cohort study.

If the population of such a study are, at baseline, divided into two If the population of such a study are, at baseline, divided into two groups, and the investigators impose a health intervention upon groups, and the investigators impose a health intervention upon one of the groups the design is that of a trial. one of the groups the design is that of a trial.

Studies based on aggregated data are commonly referred to as Studies based on aggregated data are commonly referred to as ecological studies. ecological studies.

Mostly, ecological studies are mode of analysis, rather than a Mostly, ecological studies are mode of analysis, rather than a design. design.

Interpretation and application of data are easier when the Interpretation and application of data are easier when the relationship between the population observed and the target relationship between the population observed and the target population is understoodpopulation is understood

RCTs represent the “gold standard” of research designs. They RCTs represent the “gold standard” of research designs. They thus provide the most convincing evidence of relationship thus provide the most convincing evidence of relationship between exposure and effectbetween exposure and effect....

ReferencesReferences

1.1. Porta M. Porta M. A dictionary of epidemiologyA dictionary of epidemiology. 5. 5thth edition. Oxford, New York: Oxford University Press, edition. Oxford, New York: Oxford University Press, 2008. 2008.

2.2. Rothman J, Greenland S. Rothman J, Greenland S. Modern Modern epidemiologyepidemiology. Second edition. Lippincott - . Second edition. Lippincott - Raven Publishers, 1998.Raven Publishers, 1998.

3.3. Bhopal R. Bhopal R. Study designStudy design. University of Edinburgh.. University of Edinburgh.4.4. NLM. NLM. An introduction to Clinical trialsAn introduction to Clinical trials. U.S. . U.S.

National Library of Medicine, 2004National Library of Medicine, 20045.5. Songer T. Songer T. Study designs in epidemiological Study designs in epidemiological

researchresearch. In: South Asian Cardiovascular Research . In: South Asian Cardiovascular Research Methodology Workshop. Aga-Khan and Pittsburgh Methodology Workshop. Aga-Khan and Pittsburgh universities.universities.

The Tuskegee SyphilisThe Tuskegee Syphilis ExperimentExperiment (2003) (2003) http://www.thetalkingdrum.com/tus.html

http://www.cdc.gov/mmwr/preview/mmwrhtml/http://www.cdc.gov/mmwr/preview/mmwrhtml/mm4830a1.htmmm4830a1.htm

Thanks for your kind Thanks for your kind attention attention

and listeningand listening

Epidemiology Introduction Introduction Types of Studies Types of Studies.

Documents

Transcript of Epidemiology Introduction Introduction Types of Studies Types of Studies.