A Cochrane review included 12 studies with a total of 588 subjects. Study quality was poor, sample sizes were frequently small, there was a diversity of interventions and outcomes, and many studies reported insufficient data. A meta-analysis was possible on two studies only examining the effects of relaxation therapy on PEFR which favoured the treatment group (32 l/min, 95% CI 13 to 50 l/min).
Comment: The quality of evidence is downgraded by limitations in study quality, by indirectness (differences in the interventions and the reported outcomes) and by imprecise results (limited study size for each comparison).