A comparison of crossover versus parallel-group design in the evaluation of analgesic efficacy after molar extraction.

This study compares the analgesic effects of two standard combinations (Empirin with codeine versus Mersyndol) and placebo as measured by crossover versus parallel-group design. The analgesic results obtained with three groups of 12 to 13 crossed over subjects with two extractions divided into six subgroups of five to seven subjects for each sequence were qualitatively the same and statistically at least as strong as those obtained by analysis of parallel groups of 38 to 42 extractions per group. By both methods the analgesics were statistically significantly more effective than placebo. The difference between the two products was not statistically significant, although the score for Mersyndol was somewhat better by both methods of study. The crossover data did not allow judgments concerning side effects in spite of its greater efficiency in quantifying pain relief.