Clinical trials in acute severe asthma: are type II errors important?

Many studies in acute severe asthma have had low power. Fifteen randomised double blind studies investigating the treatment of acute severe asthma published during 1974-84 were analysed for power and 95% confidence limits. Twelve studies failed to detect a significant difference in bronchodilatation produced by two treatments and reported the treatments to produce equal effect. Each study had, however, less than a 60% probability of detecting a true 25% difference in bronchodilatation.