The four random-assignment evaluations used different methods of random assignment. Both Colorado's and Minnesota's evaluations performed random assignment using a random number generated by a computer.
California's evaluation assigned cases by sorting them by case number and then using a random start and interval sampling to determine membership in the experimental and control groups. Because case numbers are assigned sequentially in each county, this method ensured that the experimental and control samples of recipient cases had exactly the same proportion of cases of different welfare tenures. If another method of random assignment had been used, there would be no guarantee that the tenure distribution of cases would be identical for the experimental and control groups, although on average the distribution of tenures would be the same for both groups.
Michigan's evaluation assigned recipient cases using the eligibility worker's caseload identification number rather than the case number. As a result, recipient cases were assigned experimental, control, or nonresearch status in groups rather than as individual cases. Caseworkers then specialized in administering the welfare rules to which their clients had been assigned. The main advantage of this method was that it ensured that recipients, and in particular recipients in the control group, did not experience the disruption of having to change caseworkers because of the implementation of the evaluation. Random assignment of applicant cases was performed using the last two digits of the head's SSN.