Читать книгу Health Psychology - Michael Murray - Страница 108

A between groups design allocates matched groups to different treatments. If the measures are taken at one time, this is called a cross-sectional design, in contrast to a longitudinal design where the groups are tested at two or more time points. When we are comparing only treatment groups, a failure to find a difference between them on the outcome measure(s) might be for one of three reasons: they are equally effective; they are equally ineffective; they are equally harmful. For this reason, one of the groups should be a control group that will enable us to discover whether the treatment(s) show a different effect from no treatment.

Ethical issues arise over the use of control groups. Not treating someone in need of treatment is unacceptable. However, if there is genuine uncertainty about what works best, it is better to compare the treatments with a control condition than to continue forever applying a treatment that may be less effective than another. Once it has been determined which therapy is the most effective, this can be offered to the control group and to all future patients (Clark-Carter and Marks, 2004).

The choice of the control condition is important. The group should receive the same amount of attention as those in the treatment condition(s). This type of control is known as a placebo control (see below) as treatment itself could have a non-specific effect to ‘please’ the client and enhance his/her well-being.

If all of the various groups’ responses are measured only after an intervention, then we haven’t really measured change. All groups, including the control group, could have changed, but from different starting positions, and failing to find a difference between the groups after the treatment could miss this. We can help to deal with this problem by using a mixed design when we measure all groups before and after the treatment. However, we would be introducing some of the difficulties mentioned above for a cross-over or within-subjects design (Clark-Carter, 1997).