Controlled Permutations

Controlled random processes are processes which are random but frequency and distribution is controlled. For example, let’s assume three different exposure times should be randomly chosen but have same frequency within one experimental session.

You can define this type of controlled randomization process in form of a block definition that lists all possible outcomes as separate trial specifications. Because trial specifications of a block definition can be executed in random order, the different outcomes appear in random order but at the end of each block all outcomes have been executed a certain number of times.