Are the brains of left-handed people anatomically different? To investigate this question, a neuroscientist conducted postmortem brain examinations in 42 people. Each person had been evaluated before death for hand
preference and categorized as consistently right-handed (CRH) or mixed-handed (MH). The table shows the results on the area of the anterior half of the corpus callosum (the structure that links the left and right hemispheres of the brain).27 The MS(within) from the ANOVA was 2,498.
GROUP MEAN SD n
|
1.
|
Males: MH
|
423
|
48
|
5
|
|
2.
|
Males: CRH
|
367
|
49
|
7
|
|
3.
|
Females: MH
|
377
|
63
|
10
|
|
4.
|
Females: CRH
|
345
|
43
|
20
|
(a) The difference between MH and CRH is 56 mm2 for males and 32 mm2 for females. Is this sufficient evidence to conclude that the corresponding population difference is greater for males than for females? Test an appropriate hypothesis. (Use a nondirectional alternative and let a = 0.10.)
(b) As an overall measure of the difference between MH and CRH, one can consider the quantity 0.5(m1 - m2) + 0.5(m3 - m4). Construct a 95% confidence interval for this quantity. (This is a sex-adjusted comparison of MH and CRH, where the reference population is 50% male and 50% female.)