Randomization and blinding
The study was triple-blind, meaning that the surgeon, the participant, and the observer were unaware of the materials and grouping: The surgeon administering the botulinum toxin was blinded to the experimental/placebo assignments and the botulinum brands. Although the numbers of units used from the brands differed, their volumes after dilution would be similar and undetectable from each other. The observers were blinded to the treatment/control assignments and to the botulinum brands as well. The patients were blinded to the grouping as well.All documents and questionnaires were coded. The coded documents were kept in sealed envelopes. The person who did the randomization also performed the concealment. She was not involved in any of the examinations.
The participants were randomized using a computer program at two levels (Excel, Microsoft, Redmond, Washington, USA). First, they were randomized into one of the two groups (experimental versus placebo) with a ratio of about 1:2. Since the study was large and multicentered, and since many people could be excluded or lost to follow-up, an exact ratio of 1:2 was not necessitated. After the first randomization, the individuals were randomized into either of the two brands of BTX-A with a ratio similar to the market share and availability of these brands. The syringes were coded and given to the surgeon who injected the botulinum toxin. The surgeon, who was the same person in all groups, performed the injection and completed the form without knowing the botulinum toxin brand and the dilution material.