Researchers have noted a decline in cognitive functioning as people age. However, the results from other research suggest that the antioxidants in foods such as blueberries can reduce and even reverse these age-related declines, at least in laboratory rats. Based on these results, one might theorise that the same antioxidants might also benefit elderly humans. A researcher is interested in testing this theory. The researcher obtains a sample ofn= 16 adults who are older than 65, and gives each participant a daily dose of a blueberry supplement that is very high in antioxidants. After taking the supplement for six months, the participants are given a standardised cognitive skills test and produce a mean score ofM= 50.2. For the general population of elderlyadults, scores on the test average = 45 and form a normal distribution with = 9.

Use the z-score statistic to answer the questions that follow.

1. State the null and alternate hypotheses for the test in symbols and words.
2. Does this sample provide enough evidence to conclude that cognitive skills scores for these elderly adults are significantly different from those of the general population? Use a two-tailed test with = .05.
3. Compute Cohen's d to measure the size of the difference.
4. Write a sentence describing the outcome of the hypothesis test and the measure of effect size as it would appear in a research report.
5. Why was the z-score the most appropriate test to use for this experiment?