Question 13

Although there is a popular belief that herbal remedies such as Gingko biloba and Ginseng may improve learning and memory in healthy adults, these effects are usually not supported by well-controlled research (Persson, Bringlov, Nilsson, & Nyberg, 2004). In a recent study, a researcher obtained a sample ofn = 16 participants and had each person take the herbal supplement every day for 90 days. At the end of the 90 days, each person took a standardized memory test. For the general population, the scores on this memory test form a normal distribution with a = 50 and = 12. The sample of research participants had an average score of M = 54.

Research Question

Did the use of herbal supplements lead to improvements in memory?

H₀: = 50

H₁: > 50

Null Hypothesis : The use of herbal supplements has no effect on memory in healthy adults.

Alternative Hypothesis : The use of herbal supplements improve memory in healthy adults.

Alpha level of = .0

Critical value = +2.57 or -2.57

Test Statistic

54-50

z _test = 12 = 1.33

16

If the researchers calculated Cohen's d for this study and found it to bed = 0.33, what size effect did they find?

1. Very small

2. Small

3. Medium

4. Large

5. Very Large