3.3 Controlled studies and randomised control trials

A controlled study is a more rigorous and formal evaluation of an intervention similar to a research experiment (see Week 1). The study typically involves two groups of participants on the autism spectrum, both larger than those used in pilot and small-scale evaluations. One group (the experimental or intervention group) receives the intervention, and the other (the control group) does not, or they receive another intervention already known to have some effect. The latter procedure is known as ‘treatment as usual’.

Ideally the two participant groups in the study should be matched on criteria such as age, IQ or severity of symptoms, before the intervention begins. After the intervention period, the two groups are compared to see if there are any differences. This comparison requires a specific measure of the skills or behaviours that the intervention is designed to target, known as the outcome measure.

Another ideal procedure for a controlled study is that participants are assigned randomly to treatment and control groups – much like drawing numbers out of a hat. This avoids factors which might bias the outcomes, for instance, that the participants in the intervention group are more high-functioning than those in the control group. The term randomised control trial (RCT) refers to a full-scale controlled evaluation involving random allocation to intervention and ‘treatment as usual’ groups, and a relatively large number of participants. RCTs are widely used to evaluate new medical interventions, and are also considered the ‘gold standard’ in the autism field. But to date, few evaluations of autism interventions have been evaluated as far as the RCT stage. We will consider why next.