Interpreting treatment effect size from single case experimental design data: a preliminary analysis of differential effects of treatments designed to increase or decrease behaviour.

BACKGROUND: Estimates of treatment effect size from single case experimental design (SCED) data may be impacted by the direction for treatment effects (i.e. ascending or descending slope for the dependent variable). Estimating effect sizes for treatments designed to decrease behaviour are potentially more restricted because the intended direction for treatment is zero (i.e. an absolute basal). Conversely, effect sizes for interventions that increase behaviour are less restricted due to a relatively unconstrained ceiling from a pure measurement standpoint (i.e. no absolute ceiling). That is, treatments that increase behaviour have a broader range of possible effect size values as the ceiling is only limited by demand characteristics and the learners' skills and motivation to exhibit the behaviour. METHOD: The current study represents a preliminary analysis of the mean and range of SCED effect sizes for treatments designed to either increase or decrease target behaviour. A within-case Cohen's d measure that was developed for SCED data was used to estimate treatment effect sizes. RESULTS: Results indicated that the mean and range of effect size values for treatments that increased behaviour were significantly greater compared with treatments that decreased behaviour. CONCLUSIONS: Results are discussed in terms of developing standards, or best practices, specific to interpreting effect size values and meeting quality control requirements for inclusion of the data set in future SCED meta-analytic studies estimating treatment effect size. Specifically, preliminary results suggest that benchmarks for low, medium and high SCED effect size values need to be developed separately for treatments that increase or decrease levels of the dependent variable.

Stereotyped behaviours as precursors of self-injurious behaviours: a longitudinal study with infants and toddlers at risk for developmental delay.

BACKGROUND: The notion that stereotypic behaviours may be precursors of self-injurious behaviour (SIB) has been considered in the past, but the available empirical evidence is still inconsistent and ambiguous. METHOD: In a longitudinal study, we collected data on stereotypic behaviour and SIB from 160 infants and toddlers who were at-risk for developmental delay. Interviews were conducted with parents at three time points during a one-year span using the Behaviour Problems Inventory-01 which contains subscales for SIB and stereotyped behaviour. We used growth modelling to estimate linear trends in several models. Model fit was evaluated according to a combination of fit statistics as is recommended in structural equation or latent variable modelling approaches such as latent growth modelling. RESULTS: In examining the relationship between stereotyped behaviours and SIB across time, the model that represented earlier stereotyped behaviour as predicting later SIB fit the data better than the other models. CONCLUSIONS: The findings corroborate the notion that stereotyped behaviour can be a precursor of SIB. If replicated by other studies, it makes a case for considering early intervening with stereotyped behaviour as a SIB prevention strategy.

Predictors of self-injurious behaviour exhibited by individuals with autism spectrum disorder.

BACKGROUND: Presence of an autism spectrum disorder is a risk factor for development of self-injurious behaviour (SIB) exhibited by individuals with developmental disorders. The most salient SIB risk factors historically studied within developmental disorders are level of intellectual disability, communication deficits and presence of specific genetic disorders. Recent SIB research has expanded the search for risk factors to include less commonly studied variables for people with developmental disorders: negative affect, hyperactivity and impulsivity. METHOD: A heterogeneous sample of 617 individuals with autism spectrum disorder diagnoses was derived from the National Database of Autism Research. Latent constructs were estimated from items of the community version of the Aberrant Behaviour Checklist. Structural equation modelling was used to assess whether impulsivity, hyperactivity, negative affect, severity of stereotypy, intellectual functioning or severity of autism symptoms predicted severity of SIB. RESULTS: Impulsivity (ß = 0.46), followed by intellectual functioning (ß = -0.39), and stereotypy (ß = 0.23) were the variables most highly predictive of increased SIB; impulsivity and stereotypy remained significant predictors of SIB after severity of autism symptoms and intelligence quotient (IQ) were controlled for. CONCLUSIONS: High levels of impulsivity and stereotypy were significant predictors of SIB in a large and diverse sample of people with confirmed autism diagnoses. Future research is needed on the effects of reducing impulsivity and stereotypy on the outcomes of treatment, early intervention and attempts to prevent the development of SIB.