Study designs of evaluations included in the review
Placebo-controlled randomised controlled trials (RCTs) and controlled clinical trials (CCTs) were eligible. The majority of the included trials were RCTs. The duration of follow-up ranged from 3 to 61 weeks (median 13).
Specific interventions included in the review
Studies of any intervention aimed at treating CFS compared with placebo were eligible. Placebo was defined as 'any therapeutic procedure which has an effect on a patient, symptom, syndrome or disease, but which is objectively without specific activity for the condition being treated'. In the analysis, interventions were classified according to the hypothesised degree of placebo response (i.e. low, medium or high) with which they were believed to be associated. Interventions based on infectious or immunological assumptions, or alternative therapies, were deemed to have a high placebo effect; interventions based on psychological or psychiatric assumptions, a low effect; and interventions with an obscure or neutral theory base (e.g. neuroendocrinological agents), a medium effect.
Participants included in the review
Adults and children diagnosed with CFS or any similar condition (e.g. myalgic encephalomyelitis, chronic fatigue immune deficiency syndrome, or chronic mononucleosis) based on any criteria were eligible. Studies focusing only on fibromyalgia were excluded. Patients from primary, secondary and tertiary care, along with those recruited through advertisements and from patient organisations, were included. The majority of the participants were female (mean age 38 years) with poor baseline functioning due to a perceived physical cause, and a mean illness duration of 62 months.
Outcomes assessed in the review
The primary outcomes of interest were categorised as either physical (e.g. fatigue, pain, sleep and functional ability) or general (e.g. quality of life, well-being, clinical improvement, and overall symptom measure) outcomes using a binary measure (e.g. improved or not, response or non-response). The majority of the included studies reported general outcomes, while all categorised the data into response and non-response. Given the heterogeneity of the measurement systems, these criteria were classified as strict or loose for the purposes of data extraction.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.