understanding multilevel analysis comic concepts for epidemiologists

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Juan MerloDepartment of Community MedicineLund University, MalmöSWEDEN

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Learning Objectives• To understand the concept of levels of

analysis• To intuitively understand the principles of

multilevel regression techniques • To intuitively understand multilevel

epidemiological concepts like– Different levels of variation– Intra-class correlation– Fixed and random effects– Compositional and contextual factors

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Performance Objectives

After this lecture the student will be able • To recognize multilevel structures • To use basic epidemiological multilevel

concepts

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Multilevel modelling is a statistical technique for the analysis of hierarchical (MULTILEVEL) data.

Many hierarchical (MULTILEVEL) data structures exist which are relevant to Public Health, in which more than one level may influence individual health.

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Understanding multilevel analysis

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To understand multilevel analysis let us create an example using

-----Places----People---Mouths --Teeth-Caries (a demineralization of the tooth surface caused by bacteria.)

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Other multilevel examples could be:

• City areas and individual blood pressure level

J Epidemiol Community Health 2001; 55: 323-.• Hospitals and individual survival after heart

failureJ Epidemiol Community Health 2001; 55:791-• Neighbourhoods and individual use of

medicationAmerican Journal of Epidemiology 2002

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Something important is being ignored…..

Caries The multilevel concept

A population of caries

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Something important is being ignored…..

The multilevel concept The tooth

A population of teeth

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Something important is still being ignored …..

The multilevel concept The mouth

A population of mouths

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Something important is still being ignored …..

The multilevel concept

A population of persons

Merlo J. 2002-05-05 12………etc…….

The multilevel concept

A population of places

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Level 1: caries Level 2: tooth Level 3: mouth Level 4: individual Level 5: Place

AT EACH LEVEL THERE ARE•Differences (random effects)•Mean characteristics (fixed effects)

The multilevel concept

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Level: mouth

•DIFFERENT LEVELS OF AGGREGATION•RELEVANT LEVELS OF ANALYSIS?•AGGREGATION /DISAGREGATION BIAS

Level: teeth

Level: individual

Level: Place

Level 1: teeth

Level 2: mouth

Level: caries

The multilevel concept

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Level 1: Place

Level: caries

Level: teeth

Level: mouth

Level: individual

ECOLOGICAL ANALYSISThe multilevel concept

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•The multilevel way of thinking is an old way in epidemiology

•Multilevel regression techniques (Hierarchic regression, mixed models)

are only a propper procedure to analyse multilevel questions

Why do we need multilevel regression techniques?

The multilevel concept

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”CLUSTERING”

If mouths have effect on teeth health, the health of the teeth in the same mouth would be similar…also

teeth’s health would be

CLUSTERED INSIDE THE MOUTHS

If there is a ”CLUSTERING” of individual in areas (teeth’s health in mounths)….we need multilevel

regression techniques