Comment on: Chronic fatigue in general practice: is counselling as good as cognitive behaviour therapy? A UK randomised trial. [Br J Gen Pract. 2001]
Ridsdale and colleagues are to be congratulated on performing a randomised controlled trial of different treatments for chronic fatigue. However, their data do not substantiate their conclusions.
The trial was set up to demonstrate that cognitive behavioural therapy was better than counselling for patients seen in general practice with fatigue symptoms. No difference in the main outcome measures was found between the intervention and control groups. This has been interpreted as showing that the two treatments are equivalent. The sample size required for, and analysis of, equivalence studies are different than those required for trials designed to show differences,2 not least the requirement that equivalence be defined before the trial starts. This trial was not designed to show equivalence. Thus, although the results for the main outcome measures are similar they should not be reported as being equivalent. Without a definition of equivalence, calculating the study’s power to show equivalence is not possible. Also, part of the conclusions depend on a sub-group analysis which, while acknowledged as being underpowered, is given more weight than is justified. If equivalence is defined as six points on the fatigue score then, in this subgroup, the trial only has a power of 36% to show equivalence based on a 95% confidence interval. With a more conservative definition of equivalence even the main study lacks power.
You can read the rest of this comment here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1313987/pdf/11458490.pdf
Source: Underwood M, Eldridge S. Chronic fatigue in general practice. Br J Gen Pract. 2001 Apr;51(465):317-8. http://www.ncbi.nlm.nih.gov/pubmed/11458490