Does ginkgo improve memory? The law allows marketers of herbs and other natural substances to make health claims that are not supported by evidence. Brands of ginkgo extract claim to "improve memory and concentration." A recent experiment found no evidence for such effects. The subjects were 230 healthy people over 60 years old. They were randomly assigned to or a placebo pill (a dummy pill that looks and tastes the same). All of the subject took a battery of tests for learning and memory before treatment started and again after six weeks.
What are the explanatory and responses variables in this experiment?
What is the experiment design in this case?