s St. John's wort effective in treating attention-deficit/hyperactivity disorder (ADHD) in hildren and adolescents? A report in a recent issue of the Journal of the American Medical Association describes a study to answer this question. A randomized, double-blind, placebo-controlled trial was conducted involving 54 children aged 6 to 17 years. Participants were randomly assigned to receive 300 mg of St. John's wort (27 subjects) or a matched placebo (27 subjects) 3 times daily for 8 weeks. Results. ADHD rating scale scores were measured. Inattentiveness improved 2.6 points with St. John's wort vs. 3.2 points with the placebo. 12. The response variable in this experiment is A) the placebo. B) the 54 children and adolescents in the study. C) St. John's wort. D) the ADHD rating scale scores.