Intended for healthcare professionals

Endgames Statistical Question

Ecological studies: advantages and disadvantages

BMJ 2014; 348 doi: (Published 02 May 2014) Cite this as: BMJ 2014;348:g2979
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}

Researchers examined the association between child wellbeing and economic status in rich developed societies. An ecological cross sectional study design was used, with 23 of the richest 50 countries in the world included in the analysis. Child wellbeing was measured by the Unicef index of child wellbeing. Three macro-economic measures were used—material living standards (average income), the scale of differentiation in social status (income inequality), and social exclusion (children in relative poverty).1

The overall Unicef index has 40 items that measure six dimensions—material wellbeing, health and safety, education, peer and family relationships, behaviours and risks, and young people’s own subjective sense of wellbeing. An item measuring relative poverty was removed before calculating the index of child wellbeing. Low scores indicated worse outcomes. Income inequality was measured as the ratio of the total annual household income received by the richest 20% of the population to that received by the poorest 20%. Therefore, larger values indicated greater inequality between the richest and poorest within a country. Child relative poverty was measured as the proportion of children aged 0-17 years in households with an income equivalent to less than the national median.

It was reported that the overall …

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