title: The Internal, External, and Diagnostic Validity of Sluggish Cognitive Tempo: A Meta-Analysis and Critical Review.
abstract: OBJECTIVE
  To conduct the first meta-analysis evaluating the internal and external validity of the sluggish cognitive tempo (SCT) construct as related to or distinct from attention-deficit/hyperactivity disorder (ADHD) and as associated with functional impairment and neuropsychological functioning.
  
  
  METHODS
  Electronic databases were searched through September 2015 for studies examining the factor structure and/or correlates of SCT in children or adults. The search procedures identified 73 papers. The core SCT behaviors included across studies, as well as factor loadings and reliability estimates, were reviewed to evaluate internal validity. Pooled correlation effect sizes using random effects models were used to evaluate SCT in relation to external validity domains (i.e., demographics, other psychopathologies, functional impairment, and neuropsychological functioning).
  
  
  RESULTS
  Strong support was found for the internal validity of the SCT construct. Specifically, across factor analytic studies including more than 19,000 individuals, 13 SCT items loaded consistently on an SCT factor as opposed to an ADHD factor. Findings also support the reliability (i.e., internal consistency, test-retest reliability, interrater reliability) of SCT. In terms of external validity, there is some indication that SCT may increase with age (r = 0.11) and be associated with lower socioeconomic status (r = 0.10). Modest (potentially negligible) support was found for SCT symptoms being higher in males than females in children (r = 0.05) but not in adults. SCT is more strongly associated with ADHD inattention (r = 0.63 in children, r = 0.72 in adults) than with ADHD hyperactivity-impulsivity (r = 0.32 in children, r = 0.46 in adults), and it likewise appears that SCT is more strongly associated with internalizing symptoms than with externalizing symptoms. SCT is associated with significant global, social, and academic impairment (r = 0.38-0.44). Effects for neuropsychological functioning are mixed, although there is initial support for SCT being associated with processing speed, sustained attention, and metacognitive deficits.
  
  
  CONCLUSIONS
  This meta-analytic review provides strong support for the internal validity of SCT and preliminary support for the external validity of SCT. In terms of diagnostic validity, there is currently not enough evidence to describe SCT in diagnostic terms. Key directions for future research are discussed, including evaluating the conceptualization of SCT as a transdiagnostic construct and the need for longitudinal research.
authors.affiliation: Division of Behavioral Medicine and Clinical Psychology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, and University of Cincinnati College of Medicine. Electronic address: stephen.becker@cchmc.org.
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Becker
authors.affiliation: University of Colorado Boulder.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Leopold
authors.affiliation: Washington State University, Pullman.
authors.forename: G Leonard
authors.initials: GL
authors.lastname: Burns
authors.affiliation: University of Alabama, Tuscaloosa.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Jarrett
authors.affiliation: Virginia Commonwealth University, Richmond.
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Langberg
authors.affiliation: Ohio University, Athens, OH.
authors.forename: Stephen A
authors.initials: SA
authors.lastname: Marshall
authors.affiliation: University of California San Francisco.
authors.forename: Keith
authors.initials: K
authors.lastname: McBurnett
authors.affiliation: Penn State Milton S. Hershey Medical Center, Hershey, PA.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Waschbusch
authors.affiliation: University of Colorado Boulder.
authors.forename: Erik G
authors.initials: EG
authors.lastname: Willcutt
mesh_terms: D000293:Adolescent; D000328:Adult; D001289:Attention Deficit Disorder with Hyperactivity / Q000175:diagnosis; D002648:Child; D002665:Child Psychiatry / Q000379:methods; D002675:Child, Preschool; D003072:Cognition Disorders / Q000175:diagnosis* / Q000523:psychology; D005260:Female; D006801:Humans; D007175:Impulsive Behavior; D008297:Male; D009483:Neuropsychological Tests; D011569:Psychiatric Status Rating Scales; D015203:Reproducibility of Results
keywords: attention-deficit/hyperactivity disorder; diagnosis; nosology; sluggish cognitive tempo; systematic review