Researchers wanted to compare the effectiveness and safety of an extract of St. John’s wort with placebo in outpatients with major depression. To do this, they recruited 200 adult outpatients diagnosed as having major depression and having a baseline Hamilton Rating Scale for Depression (HAM-D) score of at least 20. Participants were randomly assigned to receive either St. John’s wort extract, 900 milligrams per day (mg/d) for 4 weeks, increased to 1200 mg/d in the absence of an adequate response thereafter, or a placebo for 8 weeks. The response variable was the change on the HAM-D over the treatment period. After analysis of the data, it was concluded that St. John’s wort was not effective for treatment of major depression.
(a) What type of experimental design is this?
(b) What is the population that is being studied?
(c) What is the response variable in this study?
(d) What are the treatments?
(e) Identify the experimental units.
(f ) What is the control group in this study?
(g) Draw a diagram similar to Figure 7 or 8 to illustrate the design.