MUMBAI: Internal migration added Rs 15 lakh crore to states' gross domestic product, a report by SBI shows. According to the report, increase in productivity due to redistribution of human resources far outweighs the loss in GDP of states that are seeing people leave. The reportanalyses income tax returns to study the impact of circular migration on the rise of the middle class. The weighted mean income of Rs 4.4 lakh in the assessment year 2014 has increased to Rs 13 lakh. It will increase further to Rs...