BACKGROUND: Previous studies using delusion-neutral material have demonstrated that patients with schizophrenia, particularly those with delusions, display a bias against disconfirmatory evidence (BADE). In the current study we investigated the moderating impact of belief strength on this effect. METHODS: Thirty-three schizophrenia patients, 18 patients with obsessive compulsive disorder, and 25 healthy control participants, were consecutively presented with delusion-neutral statements that provided increasingly detailed information about a scenario. They were asked to re-rate the plausibility of four descriptions of the scenario. The correct ("true") interpretation appeared poor on the first statement and then increasingly gained plausibility, whereas "lure" interpretations appeared plausible initially to varying degrees, but became implausible once all information was presented. RESULTS: Schizophrenia patients displayed a BADE for strong beliefs, in that they were biased against revising their ratings of lure items in light of new disconfirming evidence compared to the mixed control group. However, like controls, patients with schizophrenia were willing to revise weak beliefs. CONCLUSION: This confirms that schizophrenia patients are generally impaired in their ability to integrate disconfirmatory evidence, even for material that does not touch on delusional themes. This response pattern was more pronounced for strong beliefs, and this may contribute to the fixation of false ideas (i.e., delusions).
