HAVE AN IMPACT
ON BRAIN SIZE?
This study was by Willerman et al., at a large
In 1991, these researchers used Magnetic
Resonance Imaging (MRI) to determine the brain
size of a sample of 40 right-handed 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).
The scans consisted of 18 horizontal MR images.
The computer counted all pixels in each of the 18
images and the total count served as an index for
ASKING “THE” QUESTION…
Does GENDER have an impact on BRAIN SIZE?
NULL: GENDER does not have an impact on
ALTERNATIVE: GENDER does have an impact on
FEMALE AND MALE BRAIN SIZE W/
sample mean 1 862,654.60 Female
stdev 1 55,893.56
pooled sample stdev 55902.456 sample size 1 20
std error 17677.909 sample mean 2 954,855.40 Male
stdev 2 55,911.35
sample size 2 20
NULL: m1 = m2 Gender does not have an impact on brain size.
ALTERNATIVE: m1 < > m2 Gender does have an impact on brain size.
one-tailed or two tailed? 2 enter only 1 or 2
type of test? T test
enter only z or t
test statistic (obs) (5.216)
critical measure 1.960 degrees of freedom 1,817,508.00
|obs| > critical?? YES
a-level 0.050 ←enter alpha level here
p-value < a-level?? YES
REJECT THE NULL!!!
REJECT THE NULL:
GENDER does not have an impact on BRAIN SIZE.
ACCEPT THE ALTERNATIVE:
GENDER does have an impact on BRAIN SIZE.