Statistical Analysis
In most cases, the exact sample size for Dixon’s UDM could not be determined in advance. When 6 crossovers (conversion from successful block to unsuccessful block or vice versa) had occurred, we ceased to recruit patient[16, 17]. We can see that at least 20–40 patients will be required to provide reliable estimates of the target dose in our simulation studies in anesthesia trials using the Dixon’s UDM[18]. Our study recruited 29 patients and achieved this goal.
To explore the target dose ED50, four statistical approaches were used, including 3 parametric estimates of dose responsive curve[18]: linear, linear-logarithmic and exponential regressions, and one nonparametric model: the centered isotonic regression, which was only for assuming a nondecreasing dose and response relationship[19].
Residual standard errors, a statistical tool to determine the goodness of fit, which analyses how well a set of data points fit with the actual model, were calculated for all four statistical approaches.