ÖйúAƬ

The question of what constitutes evidence clearly presents major problems of positioning for academics and their work ("I can't hear you ...", 26 March). The field of psychological therapies is a major site of such difficulties.

For example, the National Institute for Health and Clinical Excellence's guidelines assert that therapies for which the positivistic methodological underpinnings are at best contestable and at worst fallacious are in fact "evidence-based". And the Department of Health is moving to regulate such therapies, although the evidence that does exist indicates that such regulation will cause the field harm.

What is not clear is whether policymakers realise that they are paying lip service to the totem of putatively objective evidence, while deliberately pursuing expediency and partiality in what they choose to embrace as evidence. Perhaps the very definition of "evidence" is intrinsically malleable and open to socially and politically constructed interpretation.

If the latter, then purist rationality simply won't be enough for academics to make an impact. They may have to join the growing number of committed "activist academics" who are prepared to draw on ideology-critique, rhetoric and even polemic to make their case in a media-driven world that impacts directly, and sometimes decisively, on the policymaking process.

Richard House, Research Centre for Therapeutic Education Roehampton University.