Defining thirds of schooling years in population studies
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When the schooling years are compared between individuals having different birth years, the steep rise in schooling years in the 20th century must be taken into account. The problem has particular importance in large international population studies, such as the WHO MONICA Project and its successor, the MORGAM Project. We present an algorithm that divides the individuals into three groups on the basis of the schooling years while preserving smooth behavior of the cut-points between consecutive birth years. The usage of method is demonstrated with data from Finland, Italy, Lithuania, and Scotland, which have different patterns of the estimated tertiles of schooling years.
KeywordsCategorization Education Population studies Socio-economic risk factors
Multinational MONItoring of trends and determinants in CArdiovascular disease
MOnica Risk Genetics Archiving and Monograph
World Health Organization
The authors thank Prof. Jaakko Tuomilehto, National Public Health Institute, Prof. Abdonas Tamosiunas, Institute of Cardiology, Prof. Hugh Tunstall-Pedoe, University of Dundee, Prof. Giancarlo Cesana, Università degli studi di Milano-Bicocca and Prof. Marco Ferrario, Università degli studi dell’Insubria for making their MONICA data available and commenting the manuscript. This work was supported by the GenomEUtwin Project grant from the European Commission under the programme ‘Quality of Life and Management of the Living Resources’ of 5th Framework Programme (No. QLG2-CT-2002-01254) and by the Academy of Finland via its grant number 53646.
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