Randomization and Masking
migraine, type headache, headache
MIGRAINE, MEDICATION OVERUSE HEADACHE
We used block minimization to randomize individual participants in batches of approximately 20 to ensure we could populate the self-management groups in a timely manner. We stratified by geographical locality (Midlands and Greater London) and 6 headache types (chronic migraine, chronic tension–type headache and episodic migraine, and chronic tension–type headache; each with or without medication overuse headache). The randomization program was written specifically for this trial by Warwick Clinical Trials Unit programming team. The algorithm minimized the imbalance between the 2 trial arms using the stratifying groups and ensuring the allocation ratio fidelity. Randomization was performed by a member of staff independent of the CHESS research team. We maintained strict allocation concealment and all baseline data were collected prior to randomization. It was not possible to mask the study team and participants from the treatment allocation.