This article describes a comprehensive meta-analysis that was conducted to estimate the prevalence of attention-deficit/hyperactivity disorder (ADHD), as defined by the
Diagnostic and Statistical ...Manual of Mental Disorders, fourth edition
(DSM-IV). A systematic literature review identified 86 studies of children and adolescents (N = 163,688 individuals) and 11 studies of adults (N = 14,112 individuals) that met inclusion criteria for the meta-analysis, more than half of which were published after the only previous meta-analysis of the prevalence of ADHD was completed. Although prevalence estimates reported by individual studies varied widely, pooled results suggest that the prevalence of DSM-IV ADHD is similar, whether ADHD is defined by parent ratings, teacher ratings, or a best estimate diagnostic procedure in children and adolescents (5.9–7.1 %), or by self-report measures in young adults (5.0 %). Analyses of diagnostic subtypes indicated that the predominantly inattentive type is the most common subtype in the population, but individuals with the combined type are more likely to be referred for clinical services. Additional research is needed to determine the etiology of the higher prevalence of ADHD in males than females and to clarify whether the prevalence of ADHD varies as a function of socioeconomic status or ethnicity. Finally, there were no significant prevalent differences between countries or regions of the world after controlling for differences in the diagnostic algorithms used to define ADHD. These results provide important support for the diagnostic validity of ADHD, and argue against the hypothesis that ADHD is a cultural construct that is restricted to the United States or any other specific culture.
Background: Previous studies have identified significant variability in attention-deficit / hyperactivity disorder (ADHD) prevalence estimates worldwide, largely explained by methodological ...procedures. However, increasing rates of ADHD diagnosis and treatment throughout the past few decades have fuelled concerns about whether the true prevalence of the disorder has increased over time.
Methods: We updated the two most comprehensive systematic reviews on ADHD prevalence available in the literature. Meta-regression analyses were conducted to test the effect of year of study in the context of both methodological variables that determined variability in ADHD prevalence (diagnostic criteria, impairment criterion and source of information), and the geographical location of studies.
Results: We identified 154 original studies and included 135 in the multivariate analysis. Methodological procedures investigated were significantly associated with heterogeneity of studies. Geographical location and year of study were not associated with variability in ADHD prevalence estimates.
Conclusions: Confirming previous findings, variability in ADHD prevalence estimates is mostly explained by methodological characteristics of the studies. In the past three decades, there has been no evidence to suggest an increase in the number of children in the community who meet criteria for ADHD when standardized diagnostic procedures are followed.
Specific learning disabilities (SLDs) are highly relevant to the science and practice of psychology, both historically and currently, exemplifying the integration of interdisciplinary approaches to ...human conditions. They can be manifested as primary conditions-as difficulties in acquiring specific academic skills-or as secondary conditions, comorbid to other developmental disorders such as attention-deficit hyperactivity disorder. In this synthesis of historical and contemporary trends in research and practice, we mark the 50th anniversary of the recognition of SLDs as a disability in the United States. Specifically, we address the manifestations, occurrence, identification, comorbidity, etiology, and treatment of SLDs, emphasizing the integration of information from the interdisciplinary fields of psychology, education, psychiatry, genetics, and cognitive neuroscience. SLDs, exemplified here by specific word reading, reading comprehension, mathematics, and written expression disabilities, represent spectrum disorders, each occurring in approximately 5% to 15% of the school-aged population. In addition to risk for academic deficiencies and related functional social, emotional, and behavioral difficulties, those with SLDs often have poorer long-term social and vocational outcomes. Given the high rate of occurrence of SLDs and their lifelong negative impact on functioning if not treated, it is important to establish and maintain effective prevention, surveillance, and treatment systems involving professionals from various disciplines trained to minimize the risk and maximize the protective factors for SLDs.
One of the most prominent neuropsychologic theories of attention-deficit/hyperactivity disorder (ADHD) suggests that its symptoms arise from a primary deficit in executive functions (EF), defined as ...neurocognitive processes that maintain an appropriate problem-solving set to attain a later goal. To examine the validity of the EF theory, we conducted a meta-analysis of 83 studies that administered EF measures to groups with ADHD (total
N = 3734) and without ADHD (
N = 2969). Groups with ADHD exhibited significant impairment on all EF tasks. Effect sizes for all measures fell in the medium range (.46–.69), but the strongest and most consistent effects were obtained on measures of response inhibition, vigilance, working memory, and planning. Weaknesses in EF were significant in both clinic-referred and community samples and were not explained by group differences in intelligence, academic achievement, or symptoms of other disorders. ADHD is associated with significant weaknesses in several key EF domains. However, moderate effect sizes and lack of universality of EF deficits among individuals with ADHD suggest that EF weaknesses are neither necessary nor sufficient to cause all cases of ADHD. Difficulties with EF appear to be one important component of the complex neuropsychology of ADHD.
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.
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).
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.
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.
Sex differences in ADHD symptom severity Arnett, Anne B.; Pennington, Bruce F.; Willcutt, Erik G. ...
Journal of child psychology and psychiatry,
June 2015, Volume:
56, Issue:
6
Journal Article
Peer reviewed
Open access
Background
Males show higher rates of attention deficit hyperactivity disorder (ADHD) than do females. Potential explanations include genuine etiological differences or artifact.
Methods
2,332 twin ...and sibling youth participated in behavioral and cognitive testing. Partially competing models of symptom severity distribution differences, the mean difference, and variance difference models, were tested within a randomly selected subsample. The Delta method was used to test for mediation of sex differences in ADHD symptom severity by processing speed, inhibition and working memory.
Results
The combined mean difference and variance difference models fully explained the sex difference in ADHD symptom severity. Cognitive endophenotypes mediated 14% of the sex difference effect.
Conclusions
The sex difference in ADHD symptom severity is valid and may be due to differing genetic and cognitive liabilities between the sexes.
Sluggish cognitive tempo (SCT) is separable from attention-deficit/hyperactivity disorder (ADHD) and other psychopathologies, and growing evidence demonstrates SCT to be associated with impairment in ...both children and adults. However, it remains unclear how SCT should optimally be conceptualized. In this article, we argue that multiple models of psychopathology should be leveraged to make substantive advances to our understanding of SCT. Both categorical and dimensional approaches should be used, including the Diagnostic and Statistical Manual of Mental Disorders (DSM) nosology, the Research Domain Criteria (RDoC) initiative, and hierarchical models of psychopathology. Studies are needed to determine whether individuals categorized with SCT can be reliably identified and differentiated from individuals without SCT in pathophysiological, neuropsychological, behavioral, and daily life functioning. Studies are also needed to evaluate the validity and utility of SCT as a transdiagnostic and dimensional construct. In considering SCT as a dimensional and potentially transdiagnostic construct, we describe ways in which SCT might be examined within the RDoC framework, including negative valence systems, cognitive systems, and arousal/regulatory systems, as well as within hierarchical models of psychopathology. Conceptualizing SCT within both categorical and dimensional models of psychopathology will help to better understand the causes, developmental pathways, and clinical implications of SCT, both as a construct in its own right and also in relation to other psychopathologies.
Before assigning full etiologic validity to a psycopathologic disorder, disease theory suggests that a causal dysfunction in a mechanism within the affect individuals must be identified. Existing ...theories on attention-deficit/hyperactivity disorder (ADHD) suggest such dysfunctions in cognitive, neuropsychological, or motivational processes in the child. To date, researchers have tested these theories by comparing groups with DSM-defined ADHD to children without ADHD. Using executive functioning as an illustration of an issue that exists across all such theories, this article describes substantial overlaps in the group performance data. Thus only a subgroup may have executive deficits. Noted are other supportive data suggesting multiple pathways to ADHD. The article explores implications and recommends that future theory and research give more consideration to the probability that only a subset of behaviorally defined children will have a deficit in a given neurocognitive mechanism believed to contribute to the disorder. Creation of a provisional set of criteria in DSM-V for defining an “executive deficit type” could stimulate research to validate the first etiologic subtype of ADHD and spur the development of more sophisticated causal models, which in the longer term may give clinicians ways to target and tailor treatments.
Explaining the sex difference in dyslexia Arnett, Anne B.; Pennington, Bruce F.; Peterson, Robin L. ...
Journal of child psychology and psychiatry,
June 2017, Volume:
58, Issue:
6
Journal Article
Peer reviewed
Open access
Background
Males are diagnosed with dyslexia more frequently than females, even in epidemiological samples. This may be explained by greater variance in males’ reading performance.
Methods
We expand ...on previous research by rigorously testing the variance difference theory, and testing for mediation of the sex difference by cognitive correlates. We developed an analytic framework that can be applied to group differences in any psychiatric disorder.
Results
Males’ overrepresentation in the low performance tail of the reading distribution was accounted for by mean and variance differences across sex. There was no sex difference at the high performance tail. Processing speed (PS) and inhibitory control partially mediated the sex difference. Verbal reasoning emerged as a strength in males.
Conclusions
Our results complement a previous finding that PS partially mediates the sex difference in symptoms of attention deficit/hyperactivity disorder (ADHD), and helps explain the sex difference in both dyslexia and ADHD and their comorbidity.
The aim of this work was 2-fold: (1) to evaluate current knowledge and identify key directions in the study of sluggish cognitive tempo (SCT); and (2) to arrive at a consensus change in terminology ...for the construct that reflects the current science and may be more acceptable to researchers, clinicians, caregivers, and patients.
An international Work Group was convened that, in early 2021, compiled an online archive of all research studies on SCT and summarized the current state of knowledge, noted methodological issues, and highlighted future directions, and met virtually on 10 occasions in 2021 to discuss these topics and terminology.
Major progress has been made over the last decade in advancing our understanding of SCT across the following domains of inquiry: construct measurement and stability; genetic, environmental, pathophysiologic, and neuropsychological correlates; comorbid conditions; functional impairments; and psychosocial and medication interventions. Findings across these domains are summarized, and potential avenues to pursue in the next generation of SCT-related research are proposed. Following repeated discussions on terminology, the Work Group selected “cognitive disengagement syndrome” (CDS) to replace “SCT” as the name for this construct. This term was deemed to best satisfy considerations that should apply when selecting terms for a condition or syndrome, as it does not overlap with established terms for other constructs, is not offensive, and reflects the current state of the science.
It is evident that CDS (SCT) has reached the threshold of recognition as a distinct syndrome. Much work remains to further clarify its nature (eg, transdiagnostic factor, separate disorder, diagnostic specifier), etiologies, demographic factors, relations to other psychopathologies, and linkages to specific domains of functional impairment. Investigators are needed with interests and expertise spanning basic, clinical, and translational research to advance our understanding and to improve the lives of individuals with this unique syndrome.
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