Does taking ginkgo tablets (i. e., and extract from a tree species) twice a day provide significant improvement in mental performance? To investigate this issue, a researcher conducted a study with 150 adult subjects who took ginkgo tablets twice a day for a period of 6 months. At the end of the study, 200 variables related to the mental performance of the subjects were measured on each subject and the means compared to known means for these variables in the population of all adults. Nine of these variables were significantly better (in the sense of statistical significance) at the 5% level for the group taking the ginkgo tablets as compared to the population as a whole, and one variable was significantly better at the 1% level for the group taking the ginkgo tablets as compared to the population as a whole. Which of the following statements is the correct conclusion?

A. There is good statistical evidence that taking ginkgo tablets twice a day provides some improvement in mental performance.

B.

These results do not provide good statistical evidence that taking ginkgo tablets twice a day provides some improvement in mental performance. If 200 tests are being performed at the 5% significance level, some are bound to show statistically significant results, even if the treatment does not have any effect. It is premature to draw statistical conclusions from this study in which the percentage of significant tests is about 5%.

C.

There is good statistical evidence that taking ginkgo tablets twice a day provides improvement for the variable that was significant at the 1% level. We should be somewhat cautious about making claims for the variables that were significant at the 5% level.

D.

These results would have provided good statistical evidence that taking ginkgo tablets twice a day provides some improvement in mental performance if the number of subjects had been larger. It is premature to draw statistical conclusions from studies in which the number of subjects is less than the number of variables measured.