Moorjani et al., Genetic Evidence for Recent Population Mixture in India, The American Journal of Human Genetics (2013), http://dx.doi.org/10.1016/j.ajhg.2013.07.006
Here's the abstract:
Most Indian groups descend from a mixture of two genetically divergent populations: Ancestral North Indians (ANI) related to Central Asians, Middle Easterners, Caucasians, and Europeans; and Ancestral South Indians (ASI) not closely related to groups outside the subcontinent. The date of mixture is unknown but has implications for understanding Indian history. We report genome-wide data from 73 groups from the Indian subcontinent and analyze linkage disequilibrium to estimate ANI-ASI mixture dates ranging from about 1,900 to 4,200 years ago. In a subset of groups, 100% of the mixture is consistent with having occurred during this period. These results show that India experienced a demographic transformation several thousand years ago, from a region in which major population mixture was common to one in which mixture even between closely related groups became rare because of a shift to endogamy.
In this paper, Moorjani et al calculate ANI (Ancestral North Indian) percentage as:
From Reich et al, they changed the outgroup from Papuan to Yoruba and the ANI clade group from CEU (Utahn Whites) to Georgians. I think both are much better choices. Looking at the D-statistics in Table S2, Georgians are definitely an appropriate choice for forming a clade with ANI.
Another important result from the paper is the difference in the date of admixture for Dravidians (108 generations or 3,132 years) and Indo-Europeans (72 generations = 2,088 years).