Claims arrive randomly to the phone bank of the company.
We assigned them to treatments in two stages: first, by day of arrival and, second, by repair ID.
(1) Because of limitations in the operating system of the company we had to assign all the repairs of one day either to the control group or to the treatment groups. We flipped a coin to decide on the assignment for the first day. Then we switch daily between treatment and control so there was an even distribution among both groups in terms of day of the week, beginning and end of the month, and seasonality.
(2) All repairs were assigned an ID number. The days of treatment repairs were assigned to treatment a or b as a function of whether the repair ID number was even or odd.