Maximum Likelihood Estimation for Linear Gaussian Covariance Models

We study parameter estimation in linear Gaussian covariance models, which are $p$-dimensional Gaussian models with linear constraints on the covariance matrix. Maximum likelihood estimation for this class of models leads to a non-convex optimization problem which typically has many local maxima. Using recent results on the asymptotic distribution of extreme eigenvalues of the Wishart distribution, we provide sufficient conditions for any hill-climbing method to converge to the global maximum. Although we are primarily interested in the case in which $n>\!\!>p$, the proofs of our results utilize large-sample asymptotic theory under the scheme $n/p \to \gamma > 1$. Remarkably, our numerical simulations indicate that our results remain valid for $p$ as small as $2$. An important consequence of this analysis is that for sample sizes $n \simeq 14 p$, maximum likelihood estimation for linear Gaussian covariance models behaves as if it were a convex optimization problem

Persistence of self-injurious behaviour in autism spectrum disorder over 3 years: a prospective cohort study of risk markers

BACKGROUND: There are few studies documenting the persistence of self-injury in individuals with autism spectrum disorder (ASD) and consequently limited data on behavioural and demographic characteristics associated with persistence. In this longitudinal study, we investigated self-injury in a cohort of individuals with ASD over 3 years to identify behavioural and demographic characteristics associated with persistence. METHODS: Carers of 67 individuals with ASD (Median age of individuals with ASD in years = 13.5, Interquartile Range = 10.00–17.00), completed questionnaires relating to the presence and topography of self-injury at T(1) and three years later at T(2). Analyses were conducted to evaluate the persistence of self-injury and to evaluate the behavioural and demographic characteristics associated with persistence of self-injury. RESULTS: At T(2) self-injurious behaviour had persisted in 77.8 % of individuals. Behavioural correlates of being non-verbal, having lower ability and higher levels of overactivity, impulsivity and repetitive behaviour, were associated with self-injury at both time points. Risk markers of impulsivity (p = 0.021) and deficits in social interaction (p = 0.026) at T(1) were associated with the persistence of self-injury over 3 years. CONCLUSIONS: Impulsivity and deficits in social interaction are associated with persistent self-injury in ASD and thus may act as behavioural risk markers. The identification of these risk markers evidences a role for behaviour dysregulation in the development and maintenance of self-injury. The findings have clinical implications for proactive intervention; these behavioural characteristics may be utilised to identify ‘at risk’ individuals for whom self-injury is likely to be persistent and therefore those individuals for whom early intervention may be most warranted

Measurement properties of tools used to assess self-harm in autistic and general population adults

Autistic people are at increased risk of experiencing self-harm compared to the general population. However, it is unclear which tools are being used to assess self-harm in autistic people, or whether existing tools need to be adapted for this group. This two-stage systematic review aimed to identify tools used to assess self-harm in autistic and general population adults, evaluate these tools on their measurement properties, and make recommendations for their appropriate use in research and clinical practice. Four databases were systematically searched (PsycINFO, Embase, MEDLINE and Web of Science). Eight frequently used self-harm assessment tools were identified and assessed for risk of bias, criteria for good measurement properties, and quality of evidence using the COSMIN checklist. Of these, two tools had sufficient evidence of internal consistency (ISAS, QNSSI), and one had been frequently used with autistic adults (NSSI-AT). These three tools may have potential for use with autistic adults but require further investigation for content validity and measurement properties in the autistic population. More research and potential adaptations to current self-harm assessment tools are recommended in order to better conceptualise and understand self-harm and its measurement in autism.</p

Autism spectrum disorder phenomenology in Phelan-Mcdermid syndrome

Literature Review: Autism spectrum disorder (ASD) phenomenology is reported to be more common in some syndromes, compared to other syndromes. However, no statistical meta-analysis has yet been conducted, synthesising the prevalence data within and between syndromes. A literature search identified research reporting the prevalence of ASD phenomenology in 16 syndromes. Robust pooled prevalence estimates were generated for 12 syndromes. ASD phenomenology was evident in all syndromes and significantly more likely in all syndromes compared to the general population. Empirical Paper: The behavioural phenotype of Phelan-McDermid syndrome (PMS) is relatively unknown, but research has indicated atypically high levels of activity, impulsivity and ASD behaviours. The profile of ASD is also reported to be atypical. Carers of individuals with PMS (N=30; mean age=10.55, SD=7.08) completed questionnaires and these data were compared to data from matched samples with Fragile X and Down syndromes, and idiopathic ASD. The results revealed lower mood in individuals with PMS, but no difference in impulsivity and overactivity compared to the comparison groups. A total of 87% of individuals with PMS met criteria for ASD and 57% met criteria for autism. The profile of those who met clinical threshold for autism was homogenous, and analogous to those with idiopathic ASD