Study designs of evaluations included in the review
The review only included randomised controlled trials (RCTs; parallel or crossover design).
Specific interventions included in the review
Studies were included if the relaxation therapy involved regular self practice of a psychophysiological technique, which promotes primarily physical or mental relaxation without suggestion or repetition of phrases aimed at a specific effect on asthma. The interventions included in the review were: progressive muscle relaxation, mental and muscular relaxation, hypnotherapy, autogenic training, biofeedback training and transcendental meditation. The interventions based on yoga and breathing techniques were excluded as they had been described elsewhere.
Participants included in the review
Asthma. Studies were included if they defined asthmatic patients by American Thoracic Society (ATS) criteria or specified reversible airway constriction. Any studies involving experimentally-induced asthma, or patients suffering from other medical conditions in addition to their asthma, were excluded. Some studies focused on children, others on adults, and the remainder were mixed groups.
Outcomes assessed in the review
The inclusion criteria relating to the outcomes were not specified. The outcome measures included lung function parameters, symptom diaries, medication usage and asthma events. Lung function tests included the airway resistance, forced expiratory volume in 1 second and peak expiratory flow rate; the latter two are commonly used despite known limitations. A change in lung function of 15% or more was considered clinically relevant. Asthma events included unscheduled visits to doctors, prescriptions of antibiotics or prednisolone, and days missed from school or work.
How were decisions on the relevance of primary studies made?
The studies were included by agreement between two reviewers.