Obsessive-compulsive-like reasoning makes an unlikely catastrophe more credible.

When obsessive-compulsive (OC) patients are confronted with disorder-relevant situations, they tend to reason in chains of small steps between the current situation and a highly improbable catastrophe. It was hypothesized that this type of "perseverative reasoning" would increase the subjective likelihood of the feared catastrophe. In an experiment with 63 healthy undergraduates, we tested whether OC-like perseverative reasoning induces feelings of uncertainty about a harmful outcome and makes this outcome more credible. Furthermore, we explored whether making multiple series of events increases these effects. Participants were administered a neutral situation with a catastrophic improbable outcome. In a pre- and post-test, they rated the credibility of this outcome and feelings of uncertainty about the outcome. In between, two experimental groups were instructed to generate respectively one or five series of intermediate steps between the situation and the harmful outcome, while a control group carried out a filler task. Consistent with the predictions, perseverative reasoning enhanced the credibility of a negative, improbable outcome. However, there were no differences between the two experimental conditions (one or five reasoning chains), and perseverative reasoning did not increase uncertainty about the outcome. The OC-like generation of small steps between an innocuous situation and a negative outcome increases the credibility of a feared outcome, potentially serving to maintain obsessive-compulsive disorder (OCD) problems.