An April 9, 2002, news release from the National Institutes of Health describes a study that investigated whether the herb St. John's worst is effective for treating depression. An excerpt from this press release follows:
An extract of the herb St. John's worst was no more effective for treating major depression of moderate severity than placebo, according to research published in the April 10 issue of the Journal of the American Medical Association. The randomized, double blind trial compared treating major depression of moderate severity. The multi-site trial, involving 340 participants, also compared the FDA approved antidepressant drug sertraline to placebo as a way to measure how sensitive the trial was to detecting antidepressant effects.
A) is this an experiment or an observational study?
B) Explain what it means for this study to be ''double blind'' and also why is this an important component of the study design.