Longitudinal Trajectory Studies of Children with Autism Spectrum Disorder: A Scoping Review

Background: Longitudinal trajectory studies are well suited for generating new knowledge about developmental conditions such as autism spectrum disorder (ASD), where variation over time is known to be an important characteristic. To more clearly understand the value of such studies, there is a need for a broad exploration and mapping of the literature that produces systematic knowledge regarding 1) where and how such research has been used to date, and 2) to inform where (i.e., research gaps) and how (i.e., methodologically) future research using this design can be conducted to optimize potential for producing clinically relevant, stakeholder-informed knowledge about ASD.

Objectives: The primary objective of this scoping review is to identify, summarize and describe the breadth and characteristics of research employing a longitudinal trajectory study design (cohorts followed for three or more timepoints) to study children (0-18 years) with a confirmed diagnosis of ASD. A secondary objective is to summarize methodological strengths, challenges, and innovations. This is an exploratory study, consistent with scoping study methodology.

Methods: Following published guidance for scoping reviews, we 1) identified relevant literature through librarian-assisted searches of multiple databases (MEDLINE, EMBASE, CINAHL, PSYCInfo, ERIC, Cochrane; combining terms for ASD, pediatric age, and trajectory study design) and by reviewing full text bibliographies; 2) conducted initial title and abstract screening, and planned aspects of data extraction, in duplicate; 3) iteratively developed the extraction form and planned results summaries to address review objectives according to emergent understanding of the literature; and 4) involved stakeholders to select relevant data presentations and inform interpretations of findings.

Results: The search yielded 12,325 records after removing duplicates; initial title and abstract screening yielded 263 articles for full text retrieval. Final eligibility screening of full text is proceeding in parallel with iterative data extraction, which has yielded the preliminary findings reported here. Growth in the use of trajectory study design is recent, with approximately two-thirds of studies published since 2009. Trajectory studies vary in important respects such as how they define trajectory groups (e.g., latent statistical categories, clustered endpoints), measures used in follow-up assessments, number of data timepoints, representativeness of sampling, covariates measured (including predictors, final outcomes), and statistical power to detect covariate effects. Opportunities and challenges discussed by authors of primary studies include the ability to characterize the complexity and heterogeneity of ASD along the dimensions of age and development, the potential to account for intervention, services and other contextual effects, and the need for sampling strategies that allow for generalizing (e.g., inception cohorts, complete consecutive samples).

Conclusions: Findings from this scoping review will provide wide-ranging information about the actual and potential uses and utility of trajectory studies for producing actionable knowledge about ASD—including by identifying opportunities for addressing outcomes and research questions most relevant to stakeholders (families, self-advocates, and care professionals). They will also produce a preliminary survey of existing methodological approaches , providing a basis for future efforts to discuss and describe best practices for longitudinal research in ASD.