Since 2008, in the global art market, just five women (Yayoi Kusama, Joan Mitchell, Louise Bourgeois, Georgia O'Keeffe, and Agnes Martin) have accounted for 40% of sales of art by female artists. During the same period, the top five-selling male artists (Pablo Picasso, Andy Warhol, Zhang Daqian, Qi Baishi, and Claude Monet) have accounted for under 10% of sales of art by men. These numbers suggest that _____ is (are) greater in the female art market than the male art market.
a. Efficiency wages
b. Compensating differentials
c. The superstar effect
d. Extrinsic motivation