Cross-national comparisons of non-harmonized indicators may lead to more confusion than clarification

A newly published study showed that the life expectancy for Danes was below the European Union (EU) average. Furthermore, the study showed that healthy life years (HLYs) at 50 years of age were much higher in Denmark than in the other EU countries in 2005. However, the results of this study should be interpreted with caution.

The analyses regarding HLYs were based on the global long-term activity limitation index as a measure of disability and were included in the EU Survey on Income and Living Condition (EU-SILC). In Denmark two response categories were used to asses long-term activity limitation (yes; no) compared to three levels in all other countries (severely limited; limited but not severely; none). In addition, the wording of the question in Denmark makes cross-national comparisons even more inadequate. The questions and the response categories were revised in the Danish SILC-2008.

A comparison of the previous and the revised indicator shows that the estimated number of HLYs at 50 years of age is approximately three years lower for both men and women in 2008 than in 2005. Furthermore, in Denmark data was collected via telephone interviews or postal questionnaires. However, in almost all other countries data was collected via face-to-face interviews. It is well known that the mode of data collection may affect response distributions.

Results based on non-harmonized indicators should always be interpreted cautiously to avoid policy-makers and others reaching erroneous conclusions.