Turkish reliability and validity study of formal thought disorder applied to patients with schizophrenia and which the observations of the patients' relatives are evaluated also

Objective: Formal thought disorder has long attracted the attention of researchers. The main reasons are that thought disorders are considered one of the core symptoms of psychiatric diseases, as they can directly affect these symptoms, yielding a key effect on the course of the disease. Our aim in the study is to demonstrate the Turkish reliability and validity of Formal Thought Disorder Scale-Self/Other (FTDS-S/O) scales created by Alvaro Barrera to patients with schizophrenia. Method: Our study included 80 patients who met the diagnosis of schizophrenia according to DSM-V criteria, 37 relatives and 40 healthy control participants . A Case Report Form was given to all participants. FTDS-S, SAPS (Scale for Assessment of Positive Symptom) and SANS (Scale for Assessment of Negative Symptom) tests were applied to the patient group. FTDS-O was also applied to the relatives of the patients. Internal consistency, intraclass consistency, test-retest were evaluated as reliability measures, and item-total scores correlation was examined. In the convergent validity analysis, total scores of the SAPS scale, positive formal thought subscale, the SANS scale and alogia subscale were evaluated. In addition, factor analysis was applied to Formal Thought Disorder Scale. 40 healthy volunteers were included in the analyses to evaluate the discriminant validity. In the statistical analysis, the level of significance was set at p <0.05. Results: In the reliability study, the Cronbach's alpha value of the FTD-S was measured as 0.939. The intraclass correlation coefficient of the FTDS-S was 0.975. In the test-retest analysis, the correlation coefficient of the FTDS-S was measured as 0.965. In the item-total score correlation, the inter-item correlation of the FTDS-S varied between 0.266 and 0.757. In the factor analysis the scales demonstrated a two-factor structure. These factors are considered as negative formal thought disorder and positive formal thought disorder. Factor 1 explains 30.0% of the total variance and factor 2 explains 18.0%. In the convergent validity analysis, we compared our scale and subscales (Positive FTD and Negative FTD) with the positive formal thought disorder items as a subscale of SAPS (SAPS-Positive FTD) and the alogia items as a subscale of SANS (SANS-Alogia). The correlation coefficient of FTDS-S with the SAPS-Positive FTD subscale was 0.609, and the correlation coefficient with the SANS-Alogia subscale was measured as 0.548. The correlation coefficient between the Negative FTD subscale of FTDS-S and the SANS-Alogia subscale was 0.523; the correlation coefficient was measured as 0.525 between the Positive FTD subscale of FTDS-S and the SAPS-Positive FTD subscale. In the discriminant validity analysis, the averages of the FTDS-S, the Negative FTD subscale, and the Positive FTD subscale were compared in the patient and healthy groups. Total scores were found statistically significantly higher in the patient group (p <0.001). In ROC analyses, the areas under curve was 0.890 for the total scale score. The cut-off value for total score was determined as ≥16. Conclusion: Formal Thought Disorder Scale-Self/Other scales had good to excellent reliability and validity