Sznajder, M., and G. Adamczyk. “EVALUATION METHODS OF IDENTIFICATION INCOME DEMAND ELASTICITY COEFFICIENTS”. Acta Scientiarum Polonorum. Oeconomia, Vol. 2, no. 1, June 2003, pp. 25-42, https://js.wne.sggw.pl/index.php/aspe/article/view/3568.