A stream of qualitative research during the trial preparation and development is important to ensure that a trial is balanced.
The randomisation will be performed by dynamic allocation to protect against subversion while ensuring that each arm of the trial is balanced for the stratification variables.
Third, we tested whether the four conditions (no incentive; chance of winning one of 25 Kingfisher vouchers; chance of winning one £500 Kingfisher voucher; offer of £10 Kingfisher voucher contingent on return of a completed questionnaire) of the trial were balanced across the most powerful predictors of non-response.
After matching, the sample, when measured across trials, was balanced on baseline characteristics (table 2), although there was weak evidence that mental health differed between groups (p=0.07).
The order of playback trials was balanced across conditions, and to avoid habituation effects, playback experiments were carried out on one group with a minimum separation of 6 days.
Numbers of trials were balanced for successful and unsuccessful encoding.
Even here, where most trials are balanced, the treat-as-one-trial approach gives an incorrect answer.
Repetition- and switch-trials were balanced per block, one occurring at most 5%% more often than the other.
Target trials were balanced across positions in the mini-sequences and were equally likely to involve a gender change or not when occurring at the beginning of the mini-sequence.
Comparing, for example, the power of the test for the balanced scenario KAB = 4, KAC = 4, KBC = 4 and the imbalanced scenario KAB = 1, KAC = 4, KBC = 7 (each with 12 trials in the loop), power is higher when the distribution of trials is balanced across comparisons (ranges from 0.23 to 0.79) rather than imbalanced (ranges from 0.16 to 0.49) (see Table 2).
A key methodological issue in pragmatic trials is balancing internal and external validity[ 30].
