Research Letter: From stress to paranoia: an experimental investigation of the moderating and mediating role of reasoning biases

The threat anticipation model by Freeman et al. (2002) proposes two pathways for the development of persecutory beliefs. In one, stress-induced arousal produces an increase of negative affect which the individual misinterprets as evidence for objective threat. The other pathway proposes an increase in reasoning biases as a reaction to stress which then entails delusional interpretations of ambiguous information. Two prominent reasoning biases that have been associated with paranoid delusions are jumping-toconclusions andpersonalizing attributions for negative events (Kinderman & Bentall, 1997 ; Freeman, 2007). Both biases have occasionally been demonstrated in psychosis-prone healthy individuals (Colbert & Peters, 2002 ; Freeman et al. 2008 ; Ziegler et al. 2008) and might represent vulnerability factors for the development of paranoia. We hypothesized that reasoning biases mediate the relationship between stress and paranoia and that individualswith pronounced reasoning biases will show a stronger increase of paranoia under stress. The sample consisted of 64 undergraduate students who took part in a stress or a non-stress condition in random order. Both conditions required the completion of reasoning tasks and symptom ratings. The conditions only differed in that for the stress condition annoying building site noise (75 dB) was induced along with some difficult knowledge questions. The time interval between conditions was 4–6 days. Details on the sample and the design have been reported (Lincoln et al. 2009). Baseline vulnerability was assessed with the 42item Community Assessment of Psychic Experiences (CAPE; Stefanis et al. 2002). Paranoia was assessed with an adapted version of the 18-item self-report Paranoia Checklist (Freeman et al. 2005). Jumpingto-conclusions was assessed using a computerized version of the beads task developed by Todd S. Woodward. Participants were shown two lakes with coloured fishes in opposing ratios (80% red and 20% grey, and vice versa). Fish were caught one by one from one lake and participants were asked to decide fromwhich lake the fish were caught, being allowed to request as many fish as they wanted before deciding. Two parallel versions of the task were employed. Outcome measures for this task were presence of Jumping to Conclusions (JTC=decision after the first or second fish) and Draws to Decision (DTD=number of fish required before deciding). Attributional style was assessed using a modified version of the Internal, Personal and Situational Attributions Questionnaire (IPSAQ; Kinderman & Bentall, 1996; modification : S.M.). The score calculated for this study was the sum of percentage estimates of external personal attributions for negative events (PANE). The 32 original items were split into two parallel 16-item versions. Paired t tests with Bonferroni correction were used to test for differences in reasoning biases and paranoia within subjects (stress v. non-stress) and multilevel linear modelling (MLM) to test for interaction effects. MLM was implemented through SPSS Mixed Models, version 15 (SPSS Inc., USA) and conducted according to established guidelines (Hox, 2002). A mediation effect occurs when (1) the independent variable (IV) significantly affects the dependent variable (DV) in the absence of the mediator, (2) the IV significantly affects the mediator, (3) the mediator has a significant effect on the DV, and (4) the effect of the IV on the DV shrinks or disappears when the mediator is added to the model (Muller et al. 2005). In Table 1 it can be seen that the score for paranoia was significantly higher in the stress condition than in the nonstress condition. Thus, condition (1) was fulfilled. However, there was no significant difference between the stress and non-stress conditions for attribution and even a trend towards less DTD in the non-stress condition. Thus, condition (2) was not fulfilled and the mediation hypothesis must be discarded. To test for the moderating effect of reasoning biases we disaggregated the scores, using the mean score of each individual in reasoning tasks across the two conditions. Stress was entered as fixed and as a random predictor in Model 1 and then reasoning biases and interaction terms of reasoning biases x stress were added in separate models. Neither DTD or JTC, nor their interactions with stress, were significant predictors of paranoia. PANE was negatively related to paranoia (coefficient=x0.02, S.E.=0.01, p<0.01), indicating that persons with more personal attributions for negative events showed higher paranoia scores, but the interaction PANErstress was not negatively related. Thus, neither the mediation nor the moderation hypotheses were confirmed. Stress did not impact on Psychological Medicine (2010), 40, 169–173. f Cambridge University Press 2009