Trial participant representativeness compared to ordinary service users in a work rehabilitation setting

Study representativeness is a major concern for generalizations from trials. The extent of the problem varies with study design and context. There is a strong emphasis on developing interventions to help people remain in the work force despite mental illness. We need to know if results from upcoming trials in this area are valid for those that later might receive the services.

The AWaC trial was a multicenter RCT conducted at six different treatment centers (n = 1193). After the trial was over, the centers were upheld and run as ordinary services. At that time, we surveyed 80 ordinary service users with the same baseline questionnaire as used in the trial, and compared them with those who participated in the trial.

There were a higher proportion of people with the highest level of education (4 years or more at university/college) in the post-trial comparison sample. This sample also reported to be "dissatisfied" with their job more often, but rated their chances for return to work as "bad" less often than the ordinary trial participants. No further significant differences between the two samples in any of the other education categories, or for any of the other demographic, health or work related comparisons were found.

Participation bias is likely to depend on study context, but in the setting of a trial to help improve work participation among people who struggle with common mental disorders, the trial participants were overall very similar to those who sought the same services as ordinary practice.