Interpreting treatment effects in randomised trials

A moderate difference corresponds to a change of approximately 1.0 per question, and changes of greater than 1.5 can be considered large. [...]in a domain with four items, patients will consider a 1 point change in two or more items as important. Each patient received all three regimens and used the questionnaire to rate their quality of life in relation to their asthma at the end of each study period. 10 Difference between treatments Asthma quality of life questionnaire domains Mean P value Proportion better on salmeterol Proportion better on salbutamol or placebo Proportion who benefited No needed to treat for a single patient to benefit Salmeterol v salbutamol Symptoms 0.50