Table 3.

Spearman's correlations between the discount rates in delay discounting (k_d), probability discounting (k_p), and decay rate of SP (k_sp)

	Probability discounting (kp)	Decay rate of SP (ksp)
Delay discounting (kd)	rho(27) = 0.20, p = 0.30	rho(24) = 0.467*, p = 0.016
Probability discounting (kp)		rho(25) = -0.01, p = 0.976

A significant correlation between delay discounting and decay rate of SP was observed (Spearman's rank-order correlation, *:p < 0.05). Note that a (hyperbolic) decay rate of SP (subjective probability of obtaining a delayed reward) as a function of delay (k_sp) is defined in SP(D) = 1/(1+k_spD) (see [13]).