UNDERSTANDING MULTILEVEL ANALYSIS Comic concepts for epidemiologists

Merlo J. 2002-05-05 1

Juan MerloDepartment of Community MedicineLund University, MalmöSWEDEN

Merlo J. 2002-05-05 2

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

Merlo J. 2002-05-05 3

Performance Objectives

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

concepts

Merlo J. 2002-05-05 4

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.

Merlo J. 2002-05-05 5

Understanding multilevel analysis

Juan Merlo

EXAMPLE:In this MULTILEVEL structureBlood pressure measurements are nested within individualsIndividuals are nested within work placesWork places are nested within municipalitiesBlood pressure measurements tend to be similar within an individual !Individuals tend to be similar within a work place !Work places tend to be similar within a municipality !

Merlo J. 2002-05-05 6

To understand multilevel analysis let us create an example using

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

Merlo J. 2002-05-05 7

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

Merlo J. 2002-05-05 8

Something important is being ignored…..

Caries The multilevel concept

A population of caries

Juan Merlo

Something important is being ignored…..We can study “caries” alone as unit of analysis…However, it is intuitive that “caries” are always on a tooth…This is really true !! The same is right regarding several blood pressure measurements performed in an individual

Merlo J. 2002-05-05 9

Something important is being ignored…..

The multilevel concept The tooth

A population of teeth

Juan Merlo

It is intuitive that “caries” are always on a tooth…This is really true !! ..and the structure of the tooth may influence the status of the caries

Merlo J. 2002-05-05 10

Something important is still being ignored …..

The multilevel concept The mouth

A population of mouths

Juan Merlo

However, it is intuitive that “teeth” are always on a moth…This is really true !! ..and the structure of the moth may influence the status of the teeth

Merlo J. 2002-05-05 11

Something important is still being ignored …..

The multilevel concept

A population of persons

Juan Merlo

It is intuitive that “moths” are always in a person…Even if often (always in fact) there is only a month in a person There are variables at both levelsThis is really true !! ..and the structure of the person may influence the status of the month

Merlo J. 2002-05-05 12………etc…….


A population of places

Merlo J. 2002-05-05 13

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)


Merlo J. 2002-05-05 14

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


Merlo J. 2002-05-05 15

Level 1: Place

Level: caries

Level: teeth

Level: mouth

Level: individual

ECOLOGICAL ANALYSISThe multilevel concept

Merlo J. 2002-05-05 16

•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?


Merlo J. 2002-05-05 17

”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

Documents

UNDERSTANDING MULTILEVEL ANALYSIS Comic concepts for epidemiologists