Application of nonparametric procedure for bioassay data to the evaluation of analgesics in man

Parametric tests for bioassay data are commonly applied to scores of pain intensity and relief for the assessment of potency ratios of analgesic drugs. It has been demonstrated, however, that scores derived from semiquantitative scales often deviate from normal distribution. In addition, when scores decrease as a consequence of analgesic treatment, the variances may be nonhomogenous. Both parametric and nonparametric procedures have been employed in this study for the evaluation of results of a double-blind multicenter trial of the analgesic effect of indoprofen and ASA (both drugs at three dose levels) and placebo in episiotomy pain. There was a good agreement between potency ratios obtained with the two assays. Peak PID appeared a less efficient means of estimating potency ratio than other measurements such as SPID and TOTPAR. The nonparametric test for quantitative bioassay appears to be a valid statistical procedure for evaluating results of clinical trials, and it does not imply any assumptions as to the type of distribution of the data.