Placentation Research - Meng Hu's Blog

CHAPTER 5
acceptable IQ tasks, but some people who can name pictures of
esoteric objects like hygrometer and calyx just can’t put their ideas
into words to describe the meaning of infidelity or petulance.
Or suppose that everyone agrees that defining words is a
good way to test Gc. Which words do you choose? Are some more
important than others? Are you more intelligent if you are able
to define adverbs and adjectives rather than just nouns and
verbs? Abstract concepts versus concrete objects? Practical considerations
mean that only a few words (maybe 25 or 35) can be
included in the vocabulary test (you can’t lock a person in a room
for 48 hours and test him or her until one of you passes out).
Thus, the person’s success or failure on the specific words is only
an estimate of how many words the person knows.
ERRORS OF MEASUREMENT
Sources of error abound when measuring any skill. Sticking with
vocabulary as a measure of Gc as an illustration, people are likely
to get more words right if they are calm, rested, and attentive than
if they are tense, tired, and tuned out. Sometimes they will have
just learned a specific word or two from a recent conversation, TV
show, or school lesson. If you had tested them the previous week,
they wouldn’t have heard of the words; test them next week, and
they might display the T-O-T or tip-of-tongue phenomenon (“It’s
on the tip of my tongue, but I can’t remember it”). An examinee
might narrow down possible responses to two choices (I know a
stalagmite is either on the roof or on the floor of a cave) and have
a 50/50 chance of guessing right on any given day.
Or the same answer might be scored differently by two different
examiners, because no scoring guide, no matter how thorough,
can anticipate all possible definitions that people give
when asked, “What do we mean by obnoxious?” On Wechsler’s
scales, the scoring guide gives samples of 2-point, 1-point (partially
correct), and 0-point responses. So why do so many people
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