Authors' reply

We differ in our approach from that taken by Shepherd, in that we are advocating an empirical approach which posits hypotheses that can be and are tested. Our review of over 200 studies demonstrates how much has been learned by testing hypotheses, amassing evidence and replicating findings. ¹ Thus there is now strong and consistent evidence that delusions are associated with biases in reasoning, such as are assessed by experimental tasks and reliable interviews. These findings are important and provide an explanation of the failure to take on board all the evidence - or a failure of reality testing, as Shepherd puts it. We now therefore have secure knowledge of specific reasoning processes which may be targeted in treatment. ²

We do not agree that world beliefs are fundamentally rearranged in people with delusions. Rather, the person’s delusions can be shown to build on the pre-existing thoughts about self and world, and are actually typically preceded by periods of anxious worry. ³ Traditional views of sudden dramatic changes are not in general supported by the evidence. Although we show that there is clear evidence of the importance of emotional processes - and in some cases this can be linked to childhood trauma - we do not conclude that the delusion represents a defence. The psychoanalytic defence accounts are not supported by the evidence. Rather, anxiety and depression - and negative views of self and others - are risk factors for and commonly expressed by patients with delusions. ⁴ We consider that these research findings render delusions explicable, and may have implications for the way all clinicians engage with people with delusions.

We advocate that there is now enough certainty in the evidence base for concerted efforts to translate them into targeted treatments for delusions. It is through further trials, drawing on the evidence base which identifies mechanisms underpinning delusions, and with change in delusions as the primary outcome, that we will make progress towards alleviating the distress at the heart of delusional experience.