Ekologi Dan Krosseksional

8/3/2019 Ekologi Dan Krosseksional

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Epidemiology KeptEpidemiology Kept

SimpleSimpleSections 11.1Sections 11.1 11.3:11.3:

Ecological & CrossEcological & Cross--SectionalSectionalStudiesStudies


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IntroductionIntroduction

This presentation covers crossThis presentation covers cross--sectional andsectional andecological studiesecological studies

Ecological studies = data on individuals lackingEcological studies = data on individuals lacking

CrossCross--sectional measurements = cansectional measurements = can notnot establishestablishdefinitive timedefinitive time--sequences in individualssequences in individuals

All ecological studies are crossAll ecological studies are cross--sectionalsectional

But not all crossBut not all cross--sectional studies are ecologicalsectional studies are ecological


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11.2 Ecological Studies11.2 Ecological Studies

Unit of observation often dichotomized as:Unit of observation often dichotomized as: AggregateAggregate--level (e.g., regions)level (e.g., regions)

IndividualIndividual--level (e.g., persons)level (e.g., persons)

Studies which use aggregateStudies which use aggregate--level data are calledlevel data are calledecological studiesecological studies

WarningWarning ecological has a different meaning in otherecological has a different meaning in otheracademic contextsacademic contexts

Units of observation actually form a continuumUnits of observation actually form a continuum

person-time individuals couples families groups neighborhoods regions nations


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Ecological Study Example 1Ecological Study Example 1

Cigarette Smoking & Lung Cancer MortalityCigarette Smoking & Lung Cancer Mortality

Each observation representsaggregate data


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Cigarette Smoking & Lung Cancer MortalityCigarette Smoking & Lung Cancer Mortality

Data may be plotted toshow correlation


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% calories from fat & heart disease% calories from fat & heart disease Studies in the 1950s showedStudies in the 1950s showed

an ecological correlationan ecological correlationbetween diets high in fatsbetween diets high in fatsand cardiovascular mortalityand cardiovascular mortality


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% calories from fat & heart disease% calories from fat & heart disease Ecological studies often have poor control ofEcological studies often have poor control of

confounding variablesconfounding variables

e.g., high fat intake countries also have:e.g., high fat intake countries also have: low rates of physical activitylow rates of physical activity

high prevalence of obesityhigh prevalence of obesity

high prevalence of smokinghigh prevalence of smoking

high cholesterol consumptionhigh cholesterol consumption

yada, yada, yadayada, yada, yada

These lurking variable may explain at leastThese lurking variable may explain at leastpart of observed correlation seen in the priorpart of observed correlation seen in the priorslideslide


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ConfoundingConfounding

Elevation and Cholera Mortality (Farr, 1852)Elevation and Cholera Mortality (Farr, 1852)

William Farr used the ecological data in the data below to supportthe miasma theory and refute contagion

However, low elevation was confounded with the real risk factor:

drinking water from the polluted Thames River


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The Ecological FallacyThe Ecological Fallacy(aggregation bias)(aggregation bias)

The ecological fallacy occurs when anThe ecological fallacy occurs when anassociation seen in aggregate does not holdassociation seen in aggregate does not hold

for individualsfor individuals First documented by Robinson (1950)First documented by Robinson (1950) NegativeNegativeecological association between high % ofecological association between high % of

foreign births and illiteracy rate (foreign births and illiteracy rate (r =r = --0.62)0.62)

When data is disaggregated, there was aWhen data is disaggregated, there was apositivepositiveassociation between these factorsassociation between these factors

Reason: high immigration states in early 20Reason: high immigration states in early 20thth

century (mostly Northeast) also had better publiccentury (mostly Northeast) also had better publiceducationeducation


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Logic of the EcologicalLogic of the Ecological

Renewed interest in ecological measuresRenewed interest in ecological measures

Studies that mix aggregate observations andStudies that mix aggregate observations and

individualindividual--level observations are calledlevel observations are calledmultimulti--level designslevel designs

MultiMulti--level analysis useful in elucidating :level analysis useful in elucidating :

causal webscausal webs

interdependence between upstream factors andinterdependence between upstream factors anddownstream factorsdownstream factors


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Types of aggregateTypes of aggregate--level risklevel risk

factors (Susser, 1994)factors (Susser, 1994) Integral variablesIntegral variables factors that effect allfactors that effect all

community memberscommunity members

e.g., th

e local economye.g., th

e local economy Contextual variablesContextual variables summary ofsummary of

individual attributesindividual attributes e.g., % of calories from fate.g., % of calories from fat

Con

tagion

variablesCon

tagion

variables a property thata property thatinvolves a group outcomeinvolves a group outcome e.g., prevalence of HIV effects risk of exposuree.g., prevalence of HIV effects risk of exposure


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Illustrative ExampleIllustrative Example

Durkheims Rules of Sociologic Method (1895)Durkheims Rules of Sociologic Method (1895)

Social explanationsSocial explanationsrequire comparisonsrequire comparisons

Comparisons requireComparisons requireclassificationclassification

ClassificationClassificationrequires definition ofrequires definition offacts to be classified,facts to be classified,compared, andcompared, andexplainedexplained


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Illustrative ExampleIllustrative ExampleLe SuicideLe Suicide

(Durkheim, 1897)(Durkheim, 1897)

Use of vital statistics toUse of vital statistics toshed light on suicideshed light on suicide

ratesrates Many factors studiedMany factors studied

(age, sex, weather,(age, sex, weather,

religion, marriage,religion, marriage,social alienation, etc.)social alienation, etc.)


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Illustrative ExampleIllustrative ExampleLe SuicideLe Suicide

(Durkheim, 1897)(Durkheim, 1897) Focus in on one element of Table 11.3 (p. 199)Focus in on one element of Table 11.3 (p. 199)

Consider suicide rates (per million personConsider suicide rates (per million person--years) inyears) in7070 80 year old men80 year old men

Unmarried:Unmarried: 1,9831,983 Married:Married: 704704

Widowed:Widowed: 1,2881,288

Last three columns labeled coefficients ofLast three columns labeled coefficients ofpreservation are rate ratios (RRs)preservation are rate ratios (RRs)

RRRR Unmarried (E+) vs. Married (EUnmarried (E+) vs. Married (E--)) = 1,983 / 704 = 2.81= 1,983 / 704 = 2.81 RRRR Widowed (E+) vs. Married (EWidowed (E+) vs. Married (E--)) = 1,288 / 704 = 1.82= 1,288 / 704 = 1.82

RRRR Unmarried (E+) vs. Widowed (EUnmarried (E+) vs. Widowed (E--)) = 1,983 / 1,288 = 1.54= 1,983 / 1,288 = 1.54

Marriage (and widowhood to lesser extent) is suicideMarriage (and widowhood to lesser extent) is suicideprotectiveprotective


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Goldberger on

PellagraGoldberger on

Pellagra

Pellagra epidemics ofPellagra epidemics ofearly 1900s initiallyearly 1900s initially

thought to be ofthought to be ofinfectious origininfectious origin

Joseph Goldberger usedJoseph Goldberger usedepidemiologic studies toepidemiologic studies to

demonstrate nutritionaldemonstrate nutritionalbasis of pellagra (niacinbasis of pellagra (niacindeficiency)deficiency)


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Goldbergers (1918) Field Study of Food IntakeGoldbergers (1918) Field Study of Food Intake(Average Calories by Food Group)(Average Calories by Food Group)pp.200pp.200 -- 201201

Nonpellagrous Households Pellagrous Households

Groups of Foods

With Highest

Income

With Lowest

Income

With Lowest

Income and One orMore Cases

With Two o r MoreCases (Most ly Low

IncomeHouseholds)

Meats (exclusive ofsalt pork), eggs,milk, butter, cheese

762 639 338 270

Dried and cannedpeas and beans(exclusive ofcanned string

beans)

126 113 115 123

Wheaten flour,

bread, cakes andcrackers, cornmeal,grits, canned corn,rice

2162 2082 1752 1840

Salt pork, lard andlard substitutes

741 673 748 745

Green and cannedvegetables(exclusive of corn),

green and cannedstring beans, fruitsof all kinds

131 71 60 69

Irish and sweetpotatoes

55 53 53 46

Sugar, syrup, jelliesand jams

250 205 222 217

All foods . . . . . 4267 3836 3288 3310


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CrossCross--Sectional Survey PopularitySectional Survey Popularity

Field surveys became popular in earlyField surveys became popular in earlyand middle parts of 20and middle parts of 20thth centurycentury

During later half of 20During later half of 20thth

century,century,epidemiologists became increasinglyepidemiologists became increasinglyaware of the limitations of crossaware of the limitations of cross--sectional surveys and thus developedsectional surveys and thus developed

Cohort methodsCohort methods CaseCase--control methodscontrol methods


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Hollin

gshead & Redlich (1964)Hollin

gshead & Redlich (1964)

Prevalence per 100,000Prevalence per 100,000

Social classSocial class PsychosisPsychosis NeurosisNeurosis

HighHigh 188188 349349

ModerateModerate 291291 250250

LowLow 518518 114114Very lowVery low 15051505 9797


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Biases inBiases inHollingshead & RedlichHollingshead & Redlich

(1964)(1964) Detection (diagnostic) biasDetection (diagnostic) bias

Different diagnostic practices create artificial differences inDifferent diagnostic practices create artificial differences inincidence and prevalenceincidence and prevalence

e.g., Poor people labeled psychotic; rich people labelede.g., Poor people labeled psychotic; rich people labeledneuroticneurotic

ReverseReverse--causality biascausality bias Disease causes the exposureDisease causes the exposure

e.g., Psychosis causes low SESe.g., Psychosis causes low SES

PrevalencePrevalence--incidence biasincidence bias Difference in prevalence but not incidenceDifference in prevalence but not incidence Hollingshead later found that wealthy people wereHollingshead later found that wealthy people were nono moremore

likely to be diagnoses with neurosis, but had more persistentlikely to be diagnoses with neurosis, but had more persistentdiagnoses (probably due to different type of health carediagnoses (probably due to different type of health carecoverage)coverage)

Ekologi Dan Krosseksional

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