The Turkish Adaptation, Validity, and Reliability of the Internal States Scale

The Internal State Scale (ISS) was developed to simultaneously assess manic and depressive symptoms in bipolar disorder. In the present study, the validity and reliability of the Turkish version of ISS (ISS-TR) were examined. The present study aimed to present the psychometric properties of this scale.

The sample consisted of 200 outpatients with bipolar disorder and 49 healthy controls. Participants completed the Turkish Internal State Scale (ISS-TR), the Brief Psychiatric Rating Scale (BPRS), the Hamilton Depression Rating Scale (HDRS), and the Young Mania Rating Scale (YMRS).

Reliability analyses revealed that the Cronbach alfa coefficient of ISS was 0.88 for the whole sample. Item-total correlations ranged from 0.15 to 0.78. Two factors emerged as a result of factor analysis: "mania" and "depression-well-being." Test-retest correlations were determined for the mania subscale as r=0.654, p<0.01 and for the depression-well-being subscale as r=0.356, p<0.01. The correlations between BPRS and both subscales were quite high. The correlation between HDRS and the depression-well-being subscale was higher (r=0.475) than that between HDRS and the mania subscale, whereas the correlation between YMRS and the mania subscale was higher (r=0.818) than that between YMRS and the depression-well-being subscale. It was seen that ISS could discriminate between the clinical and healthy control samples. In addition, it was observed that the mania subscale predicted a manic period more strongly, while the depression-well-being subscale predicted a depressive period better.

ISS is a valid and reliable scale that can be used to simultaneously assess manic and depressive symptoms. It is thought that ISS will be useful in the recognition of prodromal symptoms and in the process of maintenance treatment.