The data set used by Paul and Sridhar starts with the year 1960, when per capita income in Tamil Nadu was 51 per cent higher than UP’s. In the early 1980s, this difference had narrowed to 39 per cent. However, over the following decades the gap began to rapidly grow, and in 2005 an average resident of Tamil Nadu earned 128 per cent more than an average resident of Uttar Pradesh. (Statistics available online suggest that by 2021 the gap has increased to almost 300 per cent.)
Taking the South as a whole and the North as a whole, the book found that while the two regions differed only by 39 per cent in terms of per capita income in 1960-61, forty years later the gap had widened to 101 per cent. Now, in 2021, the gap has widened much further. Currently, the average annual per capita income of the four northern states profiled by Paul and Sridhar is about US $4,000, and of the four southern states, in excess of US $10,000, or roughly 250 per cent higher.
The data analysed by Paul and Sridhar show that there are two areas in which the South has done much better than the North. First, with regard to human development indicators such as female literacy rate, infant mortality and life expectancy. Second, in areas critical to economic development such as technical education, electricity generation, and quality and extent of roads. The first set of factors prepares healthier and better educated citizens to participate in the modern economy, while the second set enables much higher rates of productivity and efficiency in manufacturing and services.
Paul and Sridhar also found that the South fares substantially better than the North on governance indicators.