The interesting fact, however, is that the placebo itself can have a measurable positive impact on the patient. It can also APPEAR to have such an effect while, in fact, nothing has changed.
How is this possible? In some cases, patients improve because they expect to improve, regardless of medical treatment. This is an example of the healing power of the mind -- and it can be real.
Patients with autism, however, tend to be young children who are unaware of the intended purpose of their treatments. So here, any improvement is observed by the caregiver, not the patient. Patients may seem to improve simply because their caregiver expects improvement.
Talk with parents of children with autism, and you may hear something like, "We tried that treatment, and it seemed to work for a while, but then it seemed to stop working." Most likely, the parent was watching extremely closely for signs of improvement immediately after the treatment was given, and saw what looked like improvements caused by the treatment. But after a while, it may have become clear that the treatment and the improvement were not, in fact, linked.
In addition to the placebo effect itself, parents of children with autism are also coping with other factors. For example, children with autism generally develop and grow. It can be hard to tell the effect of a treatment from a naturally occurring developmental step forward. What's more, most children with autism are involved with more than one treatment. It can hard to know whether improved speech is the result of speech therapy, a new diet, sensory integration therapy, or just the result of a child developing and maturing.