R-dihydroetorphine response surface; continuum of probabilities of R-dihydroetorphine–induced analgesia and respiratory depression as function of time after 12.5 ng/kg (A), 75 ng/kg (B), 125 ng/kg (C), and 150 ng/kg (D) R-dihydroetorphine. The color shading (green to yellow and red to orange) represents the context dependency of the utility functions on the postulated threshold for analgesia: deep green equals A++/R− or at least 50% analgesia/no respiratory depression; green equals A+/R− or at least 25% analgesia/no respiratory depression; yellow equals A−/R− or no analgesia/no respiratory depression; deep red equals A−/R+ or no analgesia/serious respiratory depression); dark orange equals A+/R+ or at least 25% analgesia/serious respiratory depression; orange equals A++/R+ or at least 50% analgesia/serious respiratory depression. The ratio between green and orange surfaces is 469% (12.5 ng/kg), 205% (75 ng/kg), 151% (125 ng/kg), and 133% (150 ng/kg).