Story Name: Brain Size and Intelligence

Abstract: Are the size and weight of your brain indicators of your mental
capacity? In this study by Willerman et al. (1991) the researchers use Magnetic
Resonance Imaging (MRI) to determine the brain size of the subjects. The
researchers take into account gender and body size to draw conclusions about the
connection between brain size and intelligence.

Willerman et al. (1991) conducted their study at a large southwestern university.
They selected a sample of 40 right-handed Anglo introductory psychology students
who had indicated no history of alcoholism, unconsciousness, brain damage,
epilepsy, or heart disease. These subjects were drawn from a larger pool of
introductory psychology students with total Scholastic Aptitude Test Scores
higher than 1350 or lower than 940 who had agreed to satisfy a course requirement
by allowing the administration of four subtests (Vocabulary, Similarities, Block
Design, and Picture Completion) of the Wechsler (1981) Adult Intelligence
Scale-Revised. With prior approval of the University's research review board,
students selected for MRI were required to obtain prorated full-scale IQs of
greater than 130 or less than 103, and were equally divided by sex and IQ
classification.

The MRI Scans were performed at the same facility for all 40 subjects. The scans
consisted of 18 horizontal MR images. The computer counted all pixels with
non-zero gray scale in each of the 18 images and the total count served as an
index for brain size.

A straightforward method for evaluating the relationship between brain size and
IQ scores is the correllation coefficient. For the 20 men in the study, the
researchers report correlations between IQ scores and brain sizes before and
after controlling for body size of r = 0.51 (p-value less than 0.05) and r = 0.65
(p-value less than 0.01) respectively. For the 20 women in the study, the
researchers report the corresponding correlations to be r = 0.33 (p-value not
significant) and r = 0.35 (p-value not significant). With both genders pooled the
correlation between IQ and adjusted brain size was r = 0.51 (p-value less than
0.05).



Reference: Willerman, L., Schultz, R., Rutledge, J. N., and Bigler, E. (1991),
"In Vivo Brain Size and Intelligence," Intelligence, 15, 223-228. Authorization:
Contact authors Description: Willerman et al. (1991) collected a sample of 40
right-handed Anglo introductory psychology students at a large southwestern
university. Subjects took four subtests (Vocabulary, Similarities, Block Design,
and Picture Completion) of the Wechsler (1981) Adult Intelligence Scale-Revised.
The researchers used Magnetic Resonance Imaging (MRI) to determine the brain size
of the subjects. Information about gender and body size (height and weight) are
also included. The researchers withheld the weights of two subjects and the
height of one subject for reasons of confidentiality. Number of cases: 40
Variable Names:

1.Gender: Male or Female
2.FSIQ: Full Scale IQ scores based on the four Wechsler (1981) subtests
3.VIQ: Verbal IQ scores based on the four Wechsler (1981) subtests
4.PIQ: Performance IQ scores based on the four Wechsler (1981) subtests
5.Weight: body weight in pounds
6.Height: height in inches
7.MRI_Count: total pixel Count from the 18 MRI scans

The Data: Brain Size Data Excel

Gender FSIQ VIQ PIQ Weight Height MRI_Count
Female 133 132 124 118 64.5 816932
Male 140 150 124 ¥ 72.5 1001121
Male 139 123 150 143 73.3 1038437
Male 133 129 128 172 68.8 965353
Female 137 132 134 147 65.0 951545
Female 99 90 110 146 69.0 928799
Female 138 136 131 138 64.5 991305
Female 92 90 98 175 66.0 854258
Male 89 93 84 134 66.3 904858
Male 133 114 147 172 68.8 955466
Female 132 129 124 118 64.5 833868
Male 141 150 128 151 70.0 1079549
Male 135 129 124 155 69.0 924059
Female 140 120 147 155 70.5 856472
Female 96 100 90 146 66.0 878897
Female 83 71 96 135 68.0 865363
Female 132 132 120 127 68.5 852244
Male 100 96 102 178 73.5 945088
Female 101 112 84 136 66.3 808020
Male 80 77 86 180 70.0 889083
Male 83 83 86 ¥ ¥ 892420
Male 97 107 84 186 76.5 905940
Female 135 129 134 122 62.0 790619
Male 139 145 128 132 68.0 955003
Female 91 86 102 114 63.0 831772
Male 141 145 131 171 72.0 935494
Female 85 90 84 140 68.0 798612
Male 103 96 110 187 77.0 1062462
Female 77 83 72 106 63.0 793549
Female 130 126 124 159 66.5 866662
Female 133 126 132 127 62.5 857782
Male 144 145 137 191 67.0 949589
Male 103 96 110 192 75.5 997925
Male 90 96 86 181 69.0 879987
Female 83 90 81 143 66.5 834344
Female 133 129 128 153 66.5 948066
Male 140 150 124 144 70.5 949395
Female 88 86 94 139 64.5 893983
Male 81 90 74 148 74.0 930016
Male 89 91 89 179 75.5 935863