Psychometric properties of a sluggish cognitive tempo scale in Japanese adults with and without ADHD

This study examined the psychometric properties, convergent validity, and divergent validity of a Japanese translation of Barkley (The Barkley adult ADHD rating scale-IV, Guilford Press, New York, 2011) rating scale for assessing sluggish cognitive tempo (SCT) in adults. In total, 429 Japanese adults participated across three samples: 26 diagnosed with attention-deficit/hyperactivity disorder (ADHD; ages 19-50), 81 adults without ADHD (ages 22-65), and 322 university students (ages 18-27). All participants completed rating scales of SCT, ADHD, anxiety, and depressive symptoms. A subset of participants completed the SCT measure at two time points two weeks apart. The SCT measure (5 items) showed acceptable levels of internal consistency and test-retest reliability. This scale also demonstrated convergent and discriminant validity, as evidenced by factor analyses between SCT and ADHD inattention (ADHD-IN) symptoms as well as adequate fit of a four-factor model involving SCT, ADHD-IN, ADHD-hyperactivity/impulsivity (ADHD-HI), and internalizing symptoms. Additionally, SCT and ADHD-IN dimensions were differentially associated with ADHD-HI and internalizing factors. The ADHD group scored higher on SCT ratings compared to the student and adult non-ADHD groups even after controlling for the severity of ADHD and internalizing symptoms. The 5-item SCT measure appears reliable and demonstrates preliminary evidence of validity in Japanese adults, providing initial support for the transcultural validity of the SCT construct. Additional studies are needed to further evaluate the SCT items that did not meet criteria for convergent and discriminant validity in the current study, and to examine functional outcomes of individuals recruited based on clinically elevated SCT symptoms.