Wiśniewska, J., and R. Ryś-Jurek. “Income Aggregates in Private Farms in Poland in the Years 1990-2008”. Journal of Agribusiness and Rural Development, Vol. 18, no. 4, Dec. 2010, pp. 107-18, http://www1.up.poznan.pl/jard/index.php/jard/article/view/846.