Kompa, K., and D. Witkowska. “COMPARISON OF THE OPEN INVESTMENT FUNDS EFFICIENCY AT BULL AND BEAR MARKETS”. Acta Scientiarum Polonorum. Oeconomia, Vol. 9, no. 3, Sept. 2010, pp. 169-80, https://js.wne.sggw.pl/index.php/aspe/article/view/3918.