Ok, I got confused about what studies were being referred to where, so I took some time to go through them all. The study linked in the OP doesn't actually address whether income inequality is related to "social health". It does make the claim that there are countries that are more economically successful with lower income inequality than the UK has. That doesn't really support the title of the thread "Inequality isn't related to economic success". If janitors are paid the same as doctors, who are paid the same as someone who works part time as a wedding photographer, who is paid the same as someone who works 50 hours a week as a garbage collector, who is paid the same as someone who works as a film critic, it should be glaringly obvious that all sorts of nasty effects would happen - for example, you wouldn't have any janitors because they would all want to be film critics.
The second point quoted in the OP "Wide inequalities erode the bonds of common citizenship and recognition of human dignity across economic divides" is not supported by any data or even a reference. It is simply an assertion. The rest of the statement:
A number of analysts have pointed to the ways in which large inequalities in the kinds of economic outcome we look at are associated with societies having lower levels of happiness or well-being in other respects, and to the social problems and economic costs resulting from these
Is supported only by reference to Layard (2005), which amongst other things, says that increasing wealth beyond a minimum doesn't make people happier. It doesn't address income inequality at all. I don't think the study linked in the OP supports the assertions of the poster.
As to the correlation between income inequality and "social health", after looking more closely at the components that the University of Nottingham uses to measure social health, I have low faith that the results tell us anything useful.
There are components that are not really comparable measurements between countries, such as life expectancy and infant mortality. Different countries measure those differently. For example, in the US, any infant that has taken a single breath after being removed from the mother is counted as a live birth for purposes of the infant mortality statistics regardless of birth weight or length of gestation, whereas for many other countries that is not true. The same sort of methodology differences make comparisons of life expentency between different countries problematic.
There are other components added in to the social health index that don't seem to be measures of social health. Obesity doesn't seem to me to be a valid measure of social health. Obesity's impact on health should already be included in life expectancy measures, assuming a good apples to apples life expectancy measurement is used. Homicide rate is included, and that seems to be a very valid inclusion, but then they choose as a component imprisonment. Not
crime rates, but imprisonment rates. They then further mess things up by measuring imprisonment rates differently between the US and the rest of the of the world. For international data they use "
Log of prisoners per 100,000", yet for US data it is "Prisoners per 100,000". They also include mental health as a component, which is problematic due to differing rates of diagnoses - part of which is simply fashion. I'm going to take a wild guess that there is a low rate of ADHD diagnoses in Cote d'Ivoire relative to the US. To make matters even worse, again, the mental health category is measured differently between the US and the rest of the world. I'm not sure how the teenage birth rate is indicative of the health of a society. I can see
unwed teenage births as possibly being something to include as a measure.
Why is homicide rate included but not violent crime? Why is obesity included? Why is imprisonment rate included but not crime rates? Why mental health rates? I notice that there is no category that in any way refers to freedom, nor to civil rights, which would seem to be a glaring omission to me. The idea that happiness and well-being are intertwined with freedom is over
2,000 years old. Which ironically points us back to Layard (2005) referenced in the NEP report, because one of the seven factors that most impact happiness was personal freedom accodring to Layard (2005).
http://www.infed.org/biblio/happiness_and_education.htm
Richard Layard (2005) argued that seven factors are central to happiness. Furthermore, he used research such as the US General Social Survey to establish (for the US at least) five in some sort of order of importance. Two further factors were seen as central, but could not be ranked due to lack of survey evidence.
1.Family relationships.
...
2.Financial situation.
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3.Work.
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4.Community and friends.
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5.Health.
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Also key:
Personal freedom. Happiness also depends upon the quality of the political, economic, legal and social systems in which we operate. There is some evidence that people living in stable and peaceful societies in which they have a voice and an ability to follow their interests (where it does not harm others), and in which institutions are accountable will be happier. (Lane 2000; Layard 2005: 69-70).
If someone wants to determine whether the relationship between income inequality and social health, I think the first thing they need to do is to clearly define social health. They then need to apply a consistent measurement for all subcategories, across all countries, taking care to control for cultural differences between countries (like historical rates of tobacco usage when considering life expectancy, etc).
