Figure 4.
Mean breakpoints for drug and money as a function of dose condition, with filled squares representing mean drug breakpoints and open circles representing mean money breakpoints (n=9, ±1 SEM). A main effect of dose (F[6,48]=5.2, p<.001) was detected on drug breakpoints and all breakpoints except those under the low dose of tramadol and the high dose of codeine were significantly different from placebo (Dunnett post-hoc, p <.05). A main effect of dose was also detected on money breakpoints (F[6,48]=4.8, p<.001) and all money breakpoints were significantly different from placebo (Dunnett post-hoc, p<.05).