Determination of Ratings

Studies that had a serious flaw were rated poor in quality, studies that met all criteria were rated good in quality, and the remainder of the studies were rated fair in quality. As the fair quality category is broad, studies with this rating vary in their strengths and weaknesses. The results of some fair quality studies are likely to be valid, while others are only possibly valid. A poor quality study is not valid as the results are at least as likely to reflect flaws in the study design as a true difference between the compared interventions. A serious flaw is reflected by failure to meet combinations of items on the quality assessment checklist; for example, unclear randomization and allocation concealment methods combined with differences between randomized groups at baseline in potentially prognostic characteristics and either high attrition or lack of an intention to treat analysis. Quality assessments of studies included in this review are included in the following evidence tables.