Psychometric properties of a similarity task for measuring jumping to conclusion bias in patient with Schizophrenia

Recent cognitive theories of delusions postulate that patients with schizophrenia develop delusions due to a jumping to conclusion bias. Therefore, the aim of this study was to develop a reliable and valid task (similarity task) for measuring the jumping to conclusion bias.

The method of the present study was correlational and included a number of test development procedures. The sample consisted of 45 patients with schizophrenia who were selected from about 1500 Razi and Ebnesina Hospital's inpatients during a 6 month period via convenience sampling method. Measures included similarity (Safarian, 2010) and beads tasks (Garety, 1991) and two scales for assessment of positive and negative symptoms (Andreason, 1984). The similarity task consists of 17 groups of pictures that rotate on a computer monitor with different speeds. In each trial, a picture model and three other pictures similar to picture model are presented and the subjects are asked to select the most similar picture to the picture model. Cronbach's alpha was used to indicate consistency reliability of the task. Concurrent validity was examined by correlating the scores of the new task with the scores of an established task of jumping to conclusion bias (the beads task) (Garety, 1991). Predictive validity was determined by examining the ability of the new task to predict the severity of delusions of patients with schizophrenia. Discriminative validity was determined by examining the ability of the new task to differentiate between patients with and without delusions

The similarity task showed satisfactory internal consistency, concurrent reliability, predictive and discriminative validity.

Similarity task is a reliable and valid measure of jumping to conclusion bias and can be used in future research to examine theories on delusions and hallucinations.