The linear technical-rational model has been heavily criticised as theoretically, politically and practically inadequate. The example of accommodation needs assessment as evidence for highly contentious decisions on Gypsy and Traveller caravan site provision suggests, however, that the technical-rational model has great value in coping with complexity and tension, although the evidence it provides is likely to be challenged. This paper also argues that the same process can accord to technical-rational, tactical or enlightenment models of the interface between social research and policy-making depending on the viewpoint of different actors; the balance may shift over time.