a technique to assign units of analysis (e.g., learners) to different conditions randomly – that is without any systematic basis
"Research reports from small-scale studies…rarely inform readers how the randomisation was achieved, and it has been reported that authors sometimes seem unable to provide such information when asked (by journal editors, for example). It has therefore been recommended that the technique for making a random selection should be briefly reported in methodology sections of reports along with other details of techniques used in the study" (Taber, 2019, pp.73-74)
