Should sluggish cognitive tempo symptoms be included in the diagnosis of attention-deficit/hyperactivity disorder?

OBJECTIVE

To determine the impact of including sluggish cognitive tempo items on the factor and latent class structure of attention-deficit/hyperactivity disorder (ADHD) subtypes in boys and girls.

METHOD

Parent report of two sluggish cognitive tempo items on a population-based sample of 1430 female twins and 1414 male twins were analyzed along with parent report of the 18 DSM-IV ADHD items using principal components analysis and latent class analysis.

RESULTS

The inclusion of the two sluggish cognitive tempo items resulted in distinct factor structures for boys and girls. For boys there were separate inattentive, hyperactive/impulsive, and sluggish factors. For girls there were separate inattentive/sluggish, hyperactive, and impulsive factors. In contrast, sluggish cognitive tempo items had minimal impact on the latent class structure of ADHD for both boys and girls.

CONCLUSIONS

The inclusion of sluggish cognitive tempo items markedly changed ADHD symptom associations for boys and girls in a factor analytic framework. In contrast, latent class subtyping of ADHD shows limited impact of the inclusion of sluggish cognitive tempo items, emphasizing the very different assumptions about underlying continua of behavior rather than discrete classes that distinguish the two approaches.