This design is based on the assumption that those who are currently at the termination stage of an intervention are similar in terms of the nature and extent of the problem to those who are currently at the intake stage.In order to ascertain the change that can be attributed to an intervention, a sample at the intake and termination stages of the programme is selected, so that information can be collected pertaining to pre-situations and post-situations with respect to the problem for which the intervention is being sought.To evaluate the pattern of impact, sometimes researchers collect data at one or more intermediary stages.