Pro-market policies for developing countries have long been based on the belief that increasing average income is key to improving public health and societal well-being.
But new research on India published in the journal Social Science and Medicine shows that literacy - a non-income good - has a greater impact on public health in India.
While the researchers, based at Cambridge's Department of Sociology, accept it is broadly true that "wealthier is healthier" across the roughly 500 districts in India's 'major states', accounting for 95% of the total population, they find that poverty and, crucially, illiteracy are much stronger predictors of poor public health than low average income.
A poor district can nonetheless enjoy relatively good public health if it has a high literacy rate, say researchers. Literacy acts as a base, enabling populations to understand medicine labeling, access healthcare, and engage with public health programmes.
Using data on income, education, and under-five and infant mortality, the researchers suggest that policymakers concerned with public health should focus on literacy levels rather than average income.*
Models estimate that for the 'typical' Indian district in the early 2000s, the poverty gap would have had to be reduced by 25% to save one child per thousand live births, whereas a mere 4% increase in literacy rate would have had the same effect.+
And at the level of India's 35 states and Union Territories, literacy is the only significant predictor of public health - even poverty gap is not a reliable predictor.
"Economic policies narrowly focused on growth are insufficient when it comes to public health in less developed countries," said Lawrence King, Professor of Sociology and Political Economy and co-author of the study with Cambridge colleagues Keertichandra Rajan and Jonathan Kennedy.
"Higher average income is a statistical red herring: it contributes to better public health mainly to the extent that it reflects high literacy and low poverty."
The researchers also found that although income inequality does not affect under-five and infant mortality rates in India, it does affect other measures of poor societal well-being such as self-reported ailment.
Even after they accounted for differences in individual education and income, along with average district income, people - especially women - living in districts with high levels of income inequality were significantly more likely to report an ailment than those in more equal districts.
A one-unit increase in the Gini co-efficient - the standard measure of inequality - of the 'typical' district makes people living in that district 83% more likely to report an ailment. This is despite the common belief among public health analysts that such effects of inequality are felt only in developed countries with high average incomes.
"Since our models account for differences in individual income and district average income, this is tentative evidence for the psychological and social effects of inequality in a poor country," said Rajan.
"Even if inequality does not lead to more children dying in India, it may generate individual stress and fray social bonds enough to undermine societal well-being."
Overall, researchers feel the study provides support for what its authors call the 'pro-poor position': while economic growth is certainly important, a focus on the most deprived in terms of income as well as other factors such as literacy, may be more effective than improving the average.
"Standard policy prescriptions need revision. Even in developing countries, they must be more subtle. First, non-income goods like literacy may make an important contribution to public health. Second, alleviating poverty may be more effective than raising average income levels. And third, policy should be based on a broader understanding of societal well-being and the factors that promote it."