Displacement of control group policies is the opposite of spillover, since it involves control group members failing to receive services they would have received in the absence of welfare reform. An example of displacement would be reductions in job-training services to control group members because of longer waiting lists arising from welfare reform. Usually, any displacement is the unintentional consequence of administering two welfare systems at the same research site. On rare occasions, however, displacement may arise through the intentional actions of program administrators, who may devote greater attention to ensuring that welfare reform "works" and less attention to maintaining the "old" welfare system.
As with spillover, a certain degree of displacement is likely to occur in an experimental evaluation, since the administration of two programs in the same research site may reduce the resources available for administering services to members of the control group. Nonetheless, the risk of displacement may be reduced by seeking to preserve enough administrative resources for the continuation of control group policies and by maintaining separate staff to administer experimental and control group policies to avoid any manipulation by program administrators.