11. 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 randomized comparative experiment found no statistically significant evidence for such
effects. The subjects were 350 healthy volunteers over 60 years old. They were randomly assigned to
ginkgo or a placebo pill (a dummy pill that looks and tastes the same). All the subjects took a battery of
tests for learning and memory before treatment started and again after six weeks.
(a) The study was double-blind. Why is this important?
(b) If the results were statistically significant, can the results of this study be generalized to a larger
population? Can cause-and-effect be inferred? Explain.
(0) Explain why it is advantageous to use 350 volunteers in this study, rather than, say, 30 volunteers.
(d) Name two variables that were controlled in this experiment and why was it beneficial to control these
variables?
