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. Based on past research, there is ample evidence suggesting that dementia in seniors is related to
a reduction in the volume of the hippocampus (a critical brain structure involved in memory
formation). For seniors without dementia, their average hippocampal volume is 2,556 mm3 (st
dev = 722); in contrast, for seniors with dementia, their hippocampal volume is only 2,234 mm3.
In stage one of your research, you wish to first replicate this well-established result. If you recruit
20 seniors with dementia, what is your power?
2. After replicating the previous result (question 1) and finding that seniors with dementia had
significantly smaller hippocampal volume, you wish to examine whether a new cognitive-
behavioral training program may slow down the atrophy (shrinking) of the hippocampal structure
in seniors with dementia. Recall that the hippocampal volume of those with dementia was 2,234
mm3(st dev = 722). The program is easy to administer and costs much less than other programs
currently in practice. After providing this new cognitive-behavioral training program to 50
seniors with dementia, you found that their hippocampal volume was 2455 mm3 (st dev = 675).
What do you conclude based on your data? Do the seniors with dementia enrolled in your
training program differ in terms of the size of their hippocampus compared to those with
3. You see the following in a journal article. Two equally sized groups of old and young people
were tested and young people (mean = 26.2, st dev = 2.7157) had significantly higher scores than
older people (mean = 24.05, st dev = 2.8795), (t(48)=2.71, p<.05).
a) How many people were in each group? _______
b) Calculate the effect size, using Cohen’s d?
note/hint: this can be done at least two ways, rearrange the formulas for t and d, or use the
information to calculate SS1 and SS2 to determine the weighted estimate of the variance before
calculating Cohen's d.

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