A large part of the variability in rates of autism spectrum disorders (ASD) across studies is non-aetiologic, and can be explained by differences in diagnostic criteria, case-finding method, and other issues of study design.
To investigate the effects on ASD prevalence of two methodological issues; non-response bias and case ascertainment. We compared the findings of using a semi-structured parent interview versus in-depth clinical assessment, including an ASD specific interview. We further explored whether including information on non-responders affected the ASD prevalence estimate.
A total population of 7- to 9-year olds (N = 9,430) was screened for ASD with the autism spectrum screening questionnaire (ASSQ) in the Bergen Child Study (BCS). Children scoring above the 98th percentile on parent and/or teacher ASSQ were invited to participate in the second and subsequently in the third phase of the BCS where they were assessed for ASD using the Development and Well-Being Assessment (DAWBA), and the Diagnostic Interview for Social and Communication disorders (DISCO), respectively.
Clinical assessment using DISCO confirmed all DAWBA ASD cases, but also diagnosed additional cases. DISCO-generated minimum prevalence for ASD was 0.21%, whereas estimated prevalence was 0.72%, increasing to 0.87% when adjusting for non-responders. The DAWBA estimate for the same population was 0.44%.
Large variances in prevalence rates across studies can be explained by methodological differences. Both information about assessment method and non-response are crucial when interpreting prevalence rates of ASD.
"The concept of autism has evolved from the description of severe cases of infantile autism affecting about 0.02% (Kanner, 1943), to the modern day autism spectrum disorder (ASD) encompassing an estimated 1% of the population (Baird et al., 2006; Brugha et al., 2011; Posserud, Lundervold, Lie, & Gillberg, 2010). Needless to say, the ''1% ASD'' is not the same as ''0.02% infantile autism''. "
[Show abstract][Hide abstract] ABSTRACT: With a view to developing a brief screening instrument for autism symptoms in a general population of adolescents, seven items from the Asperger syndrome (and high-functioning autism) diagnostic interview were adapted for use as self-report in an online questionnaire for youths aged 16-19 years (N=10,220). The selected items target lack of social understanding (4 items) and rigid and repetitive behavior and interests (RRBI; 3 items). Factor analyses were performed, and the seven items were also validated against self-reported ASD diagnosis. Best statistical model fit was found for a bifactor model with one general factor and two domain specific factors tied to social difficulties and RRBI. Both the general and the domain specific factors were associated with self-reported ASD diagnoses. The scale (referred to as the Autism Symptom SElf-ReporT for Adolescents and Adults - ASSERT) had good screening properties with a receiver operating curve-area under the curve (ROC-AUC) of 0.87 and a diagnostic odds ratio (DOR) of 15.8. Applying a modified scoring of the scale further improved the screening properties leading to a ROC-AUC of 0.89 and a DOR of 24.9. The ASSERT holds promise as a brief self-report screen for autism symptoms in adolescents, and further studies should explore its usefulness for adults.
Research in developmental disabilities 10/2013; 34(12). DOI:10.1016/j.ridd.2013.09.032 · 4.41 Impact Factor
"The prevalence of ASD has dramatically increased to as high as approximately 9 and 11.3 per 1,000 in the US in most recent surveys in 2006 [report, 2009] and 2008 [report, 2012], respectively, and males are more often affected than females with a ratio of 4:1 [Kogan et al., 2009; Brugha et al., 2011; Chien et al., 2011b; Kim et al., 2011]. There is a large variation in the prevalence rates between studies [Brugha et al., 2011; Kim et al., 2011] explained by varied diagnostic and methodological approaches employed as well as different levels of awareness about ASD [Posserud et al., 2010]. Due to its high prevalence, long-term impairment, high genetic component, and lack of effective prevention and treatment, ASD has been prioritized for genetic studies [Merikangas and Risch, 2003]. "
"Several reasons have been proposed to the current high prevalence, aside from a real increase: 1. the definition of autism has become broader ; 2. changes in diagnostic criteria and possible diagnostic substitution ; 3. changes in screening and diagnostic instruments for case ascertainment ; 4. changes in research methodology ; and 5. greater awareness and recognition of ASC . "
[Show abstract][Hide abstract] ABSTRACT: Background
The prevalence of autism spectrum conditions (ASC) is 1% in developed countries, but little data are available from mainland China, Hong Kong and Taiwan. This study synthesizes evidence relating to the prevalence of ASC in these areas and assesses the effects of research methodology on prevalence estimates.
Systematic literature searches were conducted in PubMed, Web of Knowledge, China Web of Knowledge and Weipu databases, as well as relevant papers published from 1987 to 2011, reporting prevalence estimates of ASC or childhood autism in mainland China, Hong Kong and Taiwan. Summary estimates of prevalence were calculated with a random effects model. The effects of research methodology on the prevalence estimates were assessed using a meta-regression model.
There were 25 studies eligible for review, 18 of which were suitable for inclusion in a meta-analysis. Pooled prevalence of childhood autism was 11.8 per 10,000 individuals (95% confidence interval (CI): 8.2, 15.3) in mainland China. Pooled prevalence of ASC was 26.6 per 10,000 (95% CI: 18.5, 34.6) in three areas. Substantial heterogeneity was identified between studies (I2>75%). The prevalence estimate of childhood autism was most strongly associated with the choice of screening instrument. After adjustment for age group, the odds ratio for prevalence estimates when using the Autism Behavior Checklist (ABC) as the screening instrument compared with those using the Clancy Autism Behavior Scale (CABS) was 0.29 (95% CI: 0.12, 0.69), and 1.79 (95% CI: 0.70, 4.55; P= 0.20) when using the Checklist for Autism in Toddlers (CHAT) compared to the CABS.
The available studies investigating the prevalence of ASC in China, Hong Kong and Taiwan have focused mainly on childhood autism rather than the whole spectrum. The prevalence estimates are lower than estimates from developed countries. Studies using more recently developed screening instruments reported higher prevalence than older ones. However, available studies have methodological weaknesses and therefore these results lack comparability with those from developed countries. Our findings indicate a potential under-diagnosis and under-detection of ASC in mainland China, Hong Kong and Taiwan, and a need to adopt more advanced methods for research of ASC in these areas.
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