“If you have borderline high blood pressure, taking magnesium supplements may help Japanese researchers report. Blood pressure fell significantly in subjects who got 400–500 milligrams of magnesium a day for four weeks, but not in those getting a placebo” (USA Weekend, 22–24 May 1998, p. 11).
a. Do you think this was a randomized experiment or an observational study? Explain.
b. Do you think the relationship found in this study is a causal one, in which taking magnesium actually causes blood pressure to be lowered? Explain.