In this study, randomly permuted blocks of size 6 are used to assign participants into two groups (treatment and placebo groups). There are 108 participants in this study and as a result, 18 blocks of size 6 is considered.
With blocks of size six, for example the order in which the integers 1,2,3,4, 5, 6 appear in a random permutation determines which patients receive the treatment (those whose numbers appear first, second and third) and which receive the placebo (those whose numbers appear fourth, fifth and sixth). For example, if numbers appear in the order of 4, 1, 6, 3, 2 and 5, the assignment of participants to the study groups will be as follows: Placebo, Treatment, Placebo, Treatment, Treatment, and Placebo. This procedure will be performed to obtain all 18 blocks of size six (1).
Fleiss JL. Design and analysis of clinical experiments: John Wiley & Sons; 2011.