Stratification, blinding and placebo effect in a clinical trial of gold bead implantation in canine Hip Dysplasia

Stratification, blinding and placebo effect in a randomised, double blind placebo-controlled clinical trial of gold bead implantation in dogs with Hip Dysplasia.The purpose of this study was to investigate the need for and choice of stratifi cation factors, and the effects of blinding and placebo in a clinical experiment. Eighty dogs with canine hip dysplasia (CHD) were included in a randomized, placebo-controlled and double blind clinical trial with stratifi ed parallel group design, in which body weight and degree of CHD were used as stratifi cation factors. Thirty-eight dogs were allocated to gold bead implantation and 42 to placebo. After six months, 33 of the 42 placebo-treated dogs received gold bead implantation in an open study lasting a further 18 months. The main outcome variable in the study was change in pain signs of CHD as assessed by the owner.No signifi cant difference in the main outcome variable, regardless of the treatment given, could be detected in the two chosen stratifi cation factors. The only factor to infl uence the main outcome variable signifi cantly was age. The blinding procedure used in the study, in which 60% of the owners correctly guessed the treatment given, was found suffi cient. Of those who guessed the treatment erroneously, 88% believed the treatment given was gold bead implantation. The treatment effi cacy after six months in the blinded treatment group was found to be signifi cantly larger compared to the effi cacy obtained in the open study. A signifi cant placebo effect was therefore detected. Conclusion and clinical relevance: The age of the dogs infl uenced the outcome of the CHD treatment, and is recommended as a stratifi cation factor. A signifi cant placebo effect has to be expected and an optimal blinding procedure is necessary in similar clinical studies.