Monday, 11 March 2013

Measuring social inequality

Some time ago I decided I would write something short and sweet about different ways of measuring social inequality. There is a chapter on this in my book on health inequality and although the book is now 10 years old in this respect little has changed. Rather disappointing in fact as we had hoped that work by us and others would soon change the ways in which inequality was measured in health studies. Not to be!

I and my colleagues still get endless papers to review that use the term 'SES' ('socio-economic status') despite this practice having been soundly criticised by Nancy Kreiger in the 1990s, and despite having taken this critique forward in our own empirical research.

What was Nancy's main point? Very simple: it is not helpful in aetiological research to mix up 3 different types of exposure: the social (class) the economic (income) and the cultural (prestige or status). It is a bit like constructing a latent variable made up of smoking, high fat diet and hours of TV watching. These factors will be found to correlate well and to predict health outcomes, but in terms of understanding how the social becomes the biological we will not be any further forward. Rather as if public health had stopped with John Snow and not bothered with microbes, or then had a category 'microbe' covering all different kinds.

What we have tried to do is use the term 'socio-economic position' (SEP) as the most general term to refer to measures of social inequality. And lets be clear here that I mean inequality between individuals not between regions, nations etc. I also get not a negligible number of papers to review that actually think Richard Wilkinson's work is something to do with health inequality (as opposed to health differences between geo-political units with different levels of income inequality). The next level down from SEP is made up of three measures: occupational social class, income, and prestige. The most carefully constructed and well validated measure of social class in use in the UK at present is known as the NS-SEC (National Statistics Socio-Economic Classification). This schema classifies occupations according to clear criteria such as whether a person is self employed or an employee, if self employed how many people they employ, if an employee the presence or absence of career opportunities, discretion over ones own work pattern, responsibility for other people's work content, and job security, summed up as "Employment relations and conditions".

Employment relations and conditions can be classified in the same way in all societies, they do not depend on local cultures. Prestige scales differ between societies and cultures. The Hindu caste system is often taught (or it was when I studied sociology) as the clearest case of a prestige system. Only people of similar caste may worship together, eat together and inter-marry. In the USA occupations have been ranked by prestige by presenting a panel of citizens with a list of occupations and asking them to assign a rank. One obvious difference between caste and the US prestige ratings is that in a caste system your prestige can emanate from your parents, caste is inherited regardless of one's occupation. So someone born into a scheduled caste (the lowest prestige) will have trouble being accepted even if they become a millionaire factory owner. I saw a similar phenomenon here in the UK when it was remarked disparageingly that the mother of Catherine Middleton had been an air stewardess. Of course we do not have caste in the UK! It is just that you can joke about the wife of the future king by calling her mother  'doors to manual', and most people will get it.

One of the sad things about mixing these dimensions on inequlity up (income is obvious so I wont elaborate) is that employment relations and prestige are accompanied by aspects of daily life that have very plausible pathways to health. Castes have different practices in terms of diet for example. Smoking has become a prestige marker in UK but not in Italy or Greece. And so on. I also wonder whether the present debate on 'micro-classes' mixes up these dimensions to some extent and creates problems for research that we don't really need to have if we just keep dimensions separate in the first place.

But this has gone on quite long enough and I will leave it to other people to let me know what they think.