General Metaanalyses

There have been several general meta-analyses of different kinds of treatment outcome for people with intellectual disabilities. (Three meta-analyses that focused exclusively on behavioural approaches are discussed later in this chapter.) They have necessarily focused on behavioural interventions because of the large number of treatment studies and extensive history of empirical research in this area. However, they have permitted direct comparison of behavioural with other treatment methods.

Scotti et al. (1991) reviewed 403 studies published from 1976 to 1987. The main behaviours of concern were stereotyped behaviour and self-injurious behaviour. Interestingly, they found that medication had the poorest impact on these problems and that interventions conducted in natural, integrated settings were more effective than those conducted when the individual was in a segregated setting. The strongest influence on outcome was whether or not the investigators had performed a functional analysis on the problem behaviour. They concluded that 'the use of functional analysis of multiple responses is perhaps a necessity for adequate treatment design' (Scotti et al., 1991, p. 252).

Didden, Duker & Korzilius (1997) reported a meta-analysis of 482 empirical studies involving 1451 comparisons of treatment with baseline. This meta-analysis included a larger range of years than that reported by Scotti et al. The most common problem behaviours were again stereotyped, self-injury, disruption and aggressive behaviour. The dependent variable for the meta-analysis was the percentage of intervention data points not overlapping with baseline data points. They found that externally directed problems, such as destructiveness and aggression towards others, were more difficult to treat than internally directed and socially disruptive problems. They found that response contingent procedures were more effective than antecedent control procedures; pharmacology; and response non-contingent procedures. Level of disability did not seem to influence either the type of intervention or the effectiveness of the intervention.

Response non-contingent procedures were superior to pharmacology. Combined behavioural treatments were superior to single behavioural treatment procedures. Finally, interventions based on functional assessment and especially functional analysis were associated with the largest effect sizes. The more precise the method used to assess the function of the target behaviour, the larger the effect sizes. Thus, larger effect sizes were associated with experimental functional analyses than with informal, descriptive functional assessment such as ABC charts, interviews and questionnaires. Therefore, the more technically sophisticated the treatment, the greater the therapeutic impact.

These two meta-analyses both reached similar conclusions: there is stronger evidence for the effectiveness of behavioural interventions than other forms of therapies, including pharmacotherapy. It is important to note that many other commonly used therapies, such as counselling, psychotherapy, sensory and dietary treatments receive little mention in these studies. This presumably reflects the absence or very small quantity of good quality evaluations of these interventions.

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