Fig. 9. A possible explanation of how the estimate of steepness of the concentration–effect relation (γ) may be biased when data from multiple patients is pooled for analysis. In this example, single data points are taken from each of nine different patients, each of whom have a steep concentration–effect relation (–) but different values of drug concentration associated with a 50% probability of drug effect (C⁵⁰). The resultant pooled concentration–effect curve (-▪-) appears flat (i.e. , the apparent value of γ is lower than the true value).