In recent years the characteristic that has strongly correlated with health problems in developed countries is income inequality. Creating an index of "Health and Social Problems" from nine factors, authors Richard Wilkinson and Kate Pickett found health and social problems "more common in countries with bigger income inequalities",Pickett and Wilkinson, The Spirit Level, 2011, pp. 306–9. Figure 2.2 found on p. 20 and this pagethe authors found a Pearson Correlation Coefficient of 0.87 for the index and inequality among 20 developed countries for which data was available. Pickett and Wilkinson, The Spirit Level, 2011, p. 310. and more common among states in the US with larger income inequalities.a coefficient of 0.59 for 40 US states for which data was available (the index for US states did not include a component for mobility in its index). For both populations the statistical significance p-value was >0.01. Pickett and Wilkinson, The Spirit Level, 2011, p. 310. Other studies have confirmed this relationship. The UNICEF index of "child well-being in rich countries", studying 40 indicators in 22 countries, correlates with greater equality but not per capita income.compare figures 2.6 and 2.7 in Pickett and Wilkinson, The Spirit Level, 2011, pp. 23–4. Data from An overview of child well-being in rich countries The United Nations Children's Fund, 2007 Pickett and Wilkinson argue that inequality and social stratification lead to higher levels of psychosocial stress and status anxiety which can lead to depression, chemical dependency, less community life, parenting problems and stress-related diseases.The Spirit Level: how 'ideas wreckers' turned book into political punchbag| Robert Booth| The Guardian| August 13, 2010
