Abstract
The purpose of this study was to investigate the need for and choice of stratification 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 stratified parallel group design, in which body weight and degree of CHD were used as stratification 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 significant difference in the main outcome variable, regardless of the treatment given, could be detected in the two chosen stratification factors. The only factor to influence the main outcome variable significantly was age. The blinding procedure used in the study, in which 60% of the owners correctly guessed the treatment given, was found sufficient. Of those who guessed the treatment erroneously, 88% believed the treatment given was gold bead implantation. The treatment efficacy after six months in the blinded treatment group was found to be significantly larger compared to the efficacy obtained in the open study. A significant placebo effect was therefore detected. Conclusion and Clinical Relevance: The age of the dogs influenced the outcome of the CHD treatment, and is recommended as a stratification factor. A significant placebo effect has to be expected and an optimal blinding procedure is necessary in similar clinical studies.
Highlights
Different treatments for canine hip dysplasia (CHD) have been described, with variable success
Methods of statistical analysis exist to compensate for unequal treatment groups, it is more convincing to present data from equivalent groups, and stratification is a method for equalizing treatment groups (Meinert 1986, Pocock 1983)
Former treatment trials of CHD with published stratification factors were not found, a related study of risk factors for degenerative joint disease associated with hip dysplasia found that body weight and hip joint laxity were such risk factors (Smith et al 2001)
Summary
Different treatments for canine hip dysplasia (CHD) have been described, with variable success. Former treatment trials of CHD with published stratification factors were not found, a related study of risk factors for degenerative joint disease associated with hip dysplasia found that body weight and hip joint laxity were such risk factors (Smith et al 2001) It may be of psychological benefit if the person reporting the treatment effect knows that the animal is receiving a new treatment. A placebo effect in companion animals that resembles those reported in human CCTs, where treatment efficacy is assessed by the dog owner several months after the treatment had been given to the dog, seems not to have been shown in veterinary clinical studies The aim of this methodology study was to examine the need for and choice of stratification factors in the treatment of canine hip dysplasia, and to investigate the effect of blinding and placebo in a controlled clinical trial of pain treatment in CHD
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