PSYC 2P25 Lecture Notes - Lecture 10: Intelligence Quotient, Magnetic Resonance Imaging, Smart People
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March 14th, 2016
IQ tests and Subtests:
measure a variety of mental abilities
report scores for overall IQ (which mainly reflects g)and for parts of the test (each of which
corresponds to a group factor)
IQ scores usually have mean of 100 and SD of 15 (calculate for a group)
IQ from intelligence quotient used to be calculated as “mental age” divided by chronological age
IQ and Brain Volume:
biological basis of IQ? Do smarter people have larger brains?
indirect evidence: head circumference has oldest link with IQ (r~.20) but head circumference
gives only a rough estimate of brain volume
brain volume measured by MRI scan gives r=.33 on average IQ
McDaniel 2005 completed 37 studies where N>1500
so, higher IQ is (moderately) related to larger brain volume
Potential Reasons for Relation Between IQ and Brain Volume:
more brain cells allow better thinking and higher IQ?
brain size and IQ both influences independently by general development and health?
brain size as a result of high IQ? (unlikely)
Note about recent MRI work on brain structure and IQ (Penke et al., 2012)
IQ correlate about .30 with brain “white matter tract integrity”
o ex. quality of neural connections between different parts of the brain
less deterioration of “wiring” makes brain work better
IQ and Life Outcomes
IQ tests contain school-like and/or puzzle/riddle-like tasks
Do IQ scores predict anything beyond academic or test-taking performance?
School Achievement has r> . 50 with IQ (this is what most people would assume-high correlation
o additionally, higher r in lower grades because of less selection (IQ tests more accurate in
elementary and high school than post secondary)
o everybody goes to elementary school so there is huge variation in how smart or not
smart people are
o in university, most people are smart (to get into post-secondary and stay there you must
be somewhat intelligent)
o therefore, not as much variability in smartness so IQ has less variability to predict
higher r for achievement tests than for course grades
o with standardized tests, there is a correct and incorrect answer
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