Study designs of evaluations included in the review
With the exception of expert opinion and descriptive studies, which were excluded, all study designs were eligible for inclusion.
Specific interventions included in the review
Studies of verbal interventions designed to influence perception of a painful stimulus were eligible for inclusion. Studies of medication or surgical interventions were excluded. The included studies used information before the painful stimulus, reinforcement with feedback between each stimulus, and coping statements. All but one of the included studies were conducted in a laboratory; the remaining study was conducted in a hospital.
Participants included in the review
Studies of adults aged 18 years or older who were able to communicate fully and had no cognitive impairment were eligible for inclusion. The pain investigated in the study had to have a clear and well-accepted pathophysiology or aetiology. Studies of patients with psychogenic or psychological pain were excluded, as were studies of terminally ill patients or patients receiving palliative or end of life care, or patients with neurological conditions.
The majority of the participants in the included studies were undergraduate students. A minority of the participants were already experiencing pain (chronic back pain). Other participants included patients requiring arteriotomies, employees of a psychiatric hospital and 'healthy' volunteers. In the included studies, pain was induced using various techniques such as electrical stimulation, a blood-pressure cuff, arteriotomy and the cold pressor test.
Outcomes assessed in the review
Studies that measured changes in the patients' perception of musculoskeletal pain, either subjectively or objectively, were eligible for inclusion. All but one of the included studies measured pain using a visual analogue scale. The studies also assessed pain threshold and pain tolerance.
How were decisions on the relevance of primary studies made?
One reviewer screened abstracts, while a second reviewer independently screened a random selection of abstracts. Inter-reviewer agreement was 100%.