Check here to estimate the number of founding populations using the method described by Leek, 20111.
Leek, J. T. 2011. Asymptotic conditional singular value decomposition for high-dimensional genomic data. Biometrics 67: 344–52.Hallin M, Liska R. 2007. Determining the number of factors in the general dynamic factor model. Journal of the American Statistical Association. 102: 603–617.