1. Merlo J. 2002-05-050 Juan Merlo Department of Community Medicine Lund University, Malmö SWEDEN

2. Merlo J. 2002-05-051 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

3. Merlo J. 2002-05-052 Performance Objectives After this lecture the student will be able To recognize multilevel structures To use basic epidemiological multilevel concepts

4. Merlo J. 2002-05-053 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.

5. Merlo J. 2002-05-054 Understanding multilevel analysis

6. Merlo J. 2002-05-055 To understand multilevel analysis let us create an example using -----Places ----People ---Mouths --Teeth -Caries (a demineralization of the tooth surface caused by bacteria.)

7. Merlo J. 2002-05-056 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 failure J Epidemiol Community Health 2001; 55:791- Neighbourhoods and individual use of medication American Journal of Epidemiology 2002

8. Merlo J. 2002-05-057 Something important is being ignored….. Caries The multilevel concept A population of caries

9. Merlo J. 2002-05-058 Something important is being ignored….. The multilevel concept The tooth A population of teeth

10. Merlo J. 2002-05-059 Something important is still being ignored ….. The multilevel concept The mouth A population of mouths

11. Merlo J. 2002-05-0510 Something important is still being ignored ….. The multilevel concept A population of persons

12. Merlo J. 2002-05-0511 ………etc……. The multilevel concept A population of places

13. Merlo J. 2002-05-0512 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

14. Merlo J. 2002-05-0513 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

15. Merlo J. 2002-05-0514 Level 1: Place Level: caries Level: teeth Level: mouth Level: individual ECOLOGICAL ANALYSIS The multilevel concept

16. Merlo J. 2002-05-0515 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

17. Merlo J. 2002-05-0516 ” 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