European Journal of Epidemiology

, Volume 30, Issue 6, pp 473–483 | Cite as

An anatomy of the way composite scores work

  • Christina BamiaEmail author
  • Dimitrios Trichopoulos


Recently, epidemiologists tend to focus on the association of health outcomes with combinations of exposures (composites), defined a-priori or a-posteriori. Such composites appear often in nutritional (dietary patterns) and genetic (genetic scores) epidemiology. The estimated associations, however, have not been linked to those of the components of the composite, at least in a systematic way. We considered composites (X) which are linear combinations of more than one exposures (components of the composite) and explored the association of X with a linear heath outcome (Y) in terms of the associations of its individual components with Y. We showed that: (1) the association of X with Y is a weighted average of the associations of the components of X with Y; (2) the weights depend on the estimated covariance matrix of the components, and on the scalar used for the linear combination, and; (3) when components are binary variables and X is a simple sum of its components, the weights depend solely on the proportion of “1”s that are present in each component and are common with the others. Using data from a cohort study in Greece we illustrated these properties for: (1) the a-priori Mediterranean diet score; (2) an a-priori genetic predisposition score, and; (3) an a-posteriori dietary pattern. Our findings may be important in interpreting estimated associations of composites with health outcomes, or, in designing composites that are expected to capture most of the associations of their components with health outcomes (new genetic scores, or composites of biomarkers).


Composite scores Dietary patterns Genetic scores A-posteriori patterns 



European Union Seventh Framework Program (FP7/2007–2013) under CHANCES Project (Grant Agreement No. HEALTH–F3-2010–242244); Hellenic Health Foundation. We thank Antonia Trichopoulou for making available EPIC-Greece data for this study.

Conflict of interest



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Copyright information

© Springer Science+Business Media Dordrecht 2015

Authors and Affiliations

  1. 1.Department of Hygiene, Epidemiology and Medical StatisticsUniversity of Athens Medical SchoolGoudi, AthensGreece
  2. 2.Hellenic Health FoundationAthensGreece
  3. 3.Department of EpidemiologyHarvard School of Public HealthBostonUSA
  4. 4.Bureau of Epidemiologic ResearchAcademy of AthensAthensGreece

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