A researcher wants to determine if an antioxidant supplement made from blueberries affects the cognitive functioning of elderly adults.  A sample of n = 16 adults between the ages of 65 and 75 is obtained.  The researcher uses a standardized test to measure cognitive performance for each individual.  The participants then begin a two-month program in which they receive daily doses of the blueberry supplement.  At the end of the two-month period, the researcher again measures cognitive performance for each participant.  The results show an average increase in performance of M_D = 7.4 with SS_D = 240.

Using a two-tailed test with a = .01, determine whether the supplement caused a significant difference in the participants’ performance on the standardized cognitive test.

 

Compute Cohen’s d to measure the effect size of the treatment.

 

Summarize the results of the study in one or more complete sentences, including an APA-style statistical statement at the end.