Every time I use the WORDSUM variable from the GSS people will complain that a score on a 10-question vocabulary test is not a good measure of intelligence. The reality is that “good” is too imprecise a term. The correlation between adult IQ and WORDSUM = 0.71. The source for this number is a 1980 paper, The Enduring Effects of Education on Verbal Skills. I’ve reproduced the relevant table…
| Estimated Correlations for Variables in a Model of Enduring Effects of Education for White, Native-Born People 25 to 72 Years Old in the Contemporary [1970s] United States | ||||||||
| Child IQ | Age | Sex | Father’s Educ | Father’s SEI | Educ | Adult IQ | WORDSUM | |
| Child IQ | - | 0 | 0 | 0.31 | 0.30 | 0.51 | 0.80 | - |
| Age | - | - | 0.026 | -0.304 | -0.130 | -0.304 | -0.42 | -0.005 |
| Sex | - | - | - | -0.054 | 0.058 | 0.050 | 0 | -0.121 |
| Father’s Educ | - | - | - | - | 0.488 | 0.469 | 0.30 | 0.302 |
| Father’s SEI | - | - | - | - | - | 0.347 | 0.31 | 0.285 |
| Educ | - | - | - | - | - | - | 0.66 | 0.511 |
| Adult IQ | - | - | - | - | - | - | - | 0.71 |
| WORDSUM | - | - | - | - | - | - | - | |
Obviously since the WORDSUM test was not given to those under 18 you can’t calculate the correlation between childhood IQ and WORDSUM score. Additionally, I suspect since 1980 there’s been a bit more cognitive stratification by education. I notice in the GSS sample that there are many older people, especially women, who have high WORDSUM scores but no college education. In the younger age cohorts this pattern is not as evident because if you are intelligent the probability is much higher that you’ll obtain a university education.
A correlation of 0.71 is not mind-blowing, there’s a significant difference between IQ and WORDSUM as they relate to each other linearly. But I think it’s good enough to get a sense that WORDSUM is a serviceable substitute for a more rigorous measure of g in lieu of any alternatives, and not so clumsy a proxy so as to be useless. Though that call is up to you, and readers are free to disagree with the methodology of the model used to obtain this correlation. Additionally, I would point out that WORDSUM is a subset of the vocabulary subsection of the Wechsler Adult Intelligence Scale. WORDSUM is in effect a slice of an IQ test.
I am bookmarking this post so that in the future I can simply place a link in the comment threads in response to objections to WORDSUM.
Note: Thanks to Bryan Caplan for pointing me to this paper.
Citation: Lee M. Wolfle, Sociology of Education, Vol. 53, No. 2 (Apr., 1980), pp. 104-114
Razib Khan’s degrees are in biochemistry and biology. He has blogged about genetics since 2002, previously worked in software development, is an Unz Foundation Junior Fellow and lives in the western US. He loves habaneros.
May 4th, 2010 at 4:06 pm
I’ve linked this paper before as well. The WORDSUM is an IQ test, and not simply a “proxy” for IQ, as many have called it. This is determined by its construct validity.
It’s clearly tapping a cognitive dimension; vocabulary strongly correlates (.83) with the general intelligence factor: content validity. The WORDSUM correlation with the AGCT is within the range that IQ tests correlate with each other: concurrent validity. It is a reliable independent predictor and predicts external outcomes in a similar manner as other IQ tests: criterion validity.
I wouldn’t recommend it for clinical or admissions purposes, but the GSS is an adequate cognitive test for the purposes of the GSS.
May 4th, 2010 at 4:14 pm
I would say that WORDSUM is useful but very limited. I easily scored 10 of 10 on it. My IQ, estimated from GRE scores, is probably in the 125 to 130 range. WORDSUM is crude. It shows that I am above average, but no more than that. Averaged across groups it gives a measure of their group intelligence. I wouldn’t want to rely on it to judge an individual.
May 4th, 2010 at 4:32 pm
tom, wordsum obviously sucks at the tails of the distribution.
May 4th, 2010 at 5:25 pm
Wordsum as a rough correlation seems ok but it has other problems. In particular, wordsum score is very highly correlated with maternal education levels (this is straight from the GSS data) . This is a serious potential confounding issue.
May 4th, 2010 at 5:39 pm
IQ tests in general are just as correlated with maternal education levels. I can’t think of a scenario where they wouldn’t be, given that a) intelligence is heritable, and b) intelligence correlates with education level.
wordsum-degree = .44
wordsum-ma degree = .24
wordsum-pa degree = .24
wordsum-spouse dg = .35
May 4th, 2010 at 7:19 pm
Is it possible to get the Wordsum test somewhere online?
May 4th, 2010 at 9:04 pm
“Obviously since the WORDSUM test was not given to those under 18 you can’t calculate the correlation between childhood IQ and WORDSUM score.”
Why not? You don’t give the WORDSUM test to children, you give it to an adult, then correlate to their childhood IQ. (Just like when you examine the correlation between Adult IQ and Childhood IQ). Or am I missing something here?
May 4th, 2010 at 10:13 pm
[...] may have seen it yourself, but wondered why people believe there is a correlation between the two. Razib Khan wrote up a nice post that explains it. Every time I use the WORDSUM variable from the GSS people will [...]
May 5th, 2010 at 3:02 am
Apparently the ten WORDSUM words have always been the same. The list of words and the six options for each can easily be found with Google. I got 10/10, even though I am not a native English speaker, and my IQ is not off the charts by any means.
May 8th, 2010 at 9:12 pm
That correlation figure (0.71) has a suspiciously high precision given that it came from a 10 question test. I’m no statistician, and I’m only browsing through, but I’d approach this whole matter with a healthy dose of scepticism.