Study designs of evaluations included in the review
Placebo-controlled studies were included in the review.
Specific interventions included in the review
Studies that compared the use of echinacea with a placebo that used inactive ingredients only were included in the review. Studies that included another active treatment in addition to echinacea were excluded, as were studies looking at the use of echinacea for the prevention of the common cold. Dosages of echinacea, number of doses per day, and the form in which echinacea was administered varied across the studies.
Participants included in the review
Studies of individuals with the common cold were included. The definitions of a cold varied considerably across the included studies. Studies of both adults and of children appear to have been included.
Outcomes assessed in the review
No inclusion criteria for the outcomes were stated. The outcomes in the included studies related to the symptoms, severity and duration of the common cold.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.