Fig. 5. The relation between measured propofol concentration, bispectral index (BIS), Pa amplitude, Nb amplitude, Pa latency, Nb latency, and probability of a positive response (0–100% probability) to verbal command were determined using logistic regression analysis of a quantal endpoint (conscious–unconscious) for all volunteers receiving either propofol alone (solid line) or propofol and alfentanil 100 ng/ml (dotted line).