Tag Archives: Intelligence quotient

Was Cyril Burt guilty of fraud?

28 Feb

The British psychologist Cyril Burt is probably most know today for having published faked data that purported to demonstrate the central role of heredity in human affairs. Most people probably know of about this case from the account in Steven Jay Gould‘s book The Mismeasure of Man. Unfortunately, Gould’s book, which includes a useful account of the distorting effects of racism on science, is marred by a number of scholarly errors.

The argument against Burt was largely based on an analysis of his data, suggesting that his results were statistically impossible. However, in a paper published in the journal Intelligence,  Gavan Tredoux has reanalyzed the data and reached different conclusions:

“In the last comprehensive review by Mackintosh et al. Cyril Burt, Fraud or Framed? (London: Oxford University Press, 1995) of the fraud charges posthumously leveled against the once eminent psychologist Sir Cyril Burt, Mackintosh and Mascie-Taylor asserted that statistical anomalies they detected in his social mobility data of 1961 provided crucial evidence of guilt. The anomalies included apparent departures from normality in some parts of the data, incommensurate cell totals, and suspicious uniformity within IQ bands across fathers and sons. It is shown here that the departures from normality were a natural consequence of unavoidable rounding when inverting the cumulative normal distribution to construct the class IQ bands used in the tables. Elementary procedures are given, known since at least the 1930s, which could have been used by Burt to simultaneously preserve both the normality of his IQ data and the desired population proportions of occupational classes. Other anomalies first noticed by the statistician Donald Rubin are explainable as artifacts produced by fixing marginal totals in the presence of rounding to IQ scores, then using the same weighting procedures to conform to margins. The grounds given by Mackintosh and Mascie-Taylor for finding fraud in Burt’s social mobility data are therefore dismissed.’

Note even if Burt’s data turns out to have been accurate there is still room for very different interpretations of these results.


Developmental changes in cognitive ability: Implications for value added measures

2 Jan

A paper published in the most recent issue of the journal Intelligence has important implications for value added measures of teaching. Here is the abstract, I have underlined the relevant sentences:

“Low socioeconomic status (SES) children perform on average worse on intelligence tests than children from higher SES backgrounds, but the developmental relationship between intelligence and SES has not been adequately investigated. Here, we use latent growth curve (LGC) models to assess associations between SES and individual differences in the intelligence starting point (intercept) and in the rate and direction of change in scores (slope and quadratic term) from infancy through adolescence in 14,853 children from the Twins Early Development Study (TEDS), assessed 9 times on IQ between the ages of 2 and 16 years. SES was significantly associated with intelligence growth factors: higher SES was related both to a higher starting point in infancy and to greater gains in intelligence over time. Specifically, children from low SES families scored on average 6 IQ points lower at age 2 than children from high SES backgrounds; by age 16, this difference had almost tripled. Although these key results did not vary across girls and boys, we observed gender differences in the development of intelligence in early childhood. Overall, SES was shown to be associated with individual differences in intercepts as well as slopes of intelligence. However, this finding does not warrant causal interpretations of the relationship between SES and the development of intelligence.”

It is well understood that children in a classroom start at different levels, valued added assessment attempts to control for this by comparing gain scores. In other words, the child’s test score at the beginning of the school year is subtracted from the child’s score at the end of year. The increase is assumed to be the value added to the student by the teacher.

However, this stands on the assumption that children learn at the same rate. This paper (“Socioeconomic status and the growth of intelligence from infancy through adolescence”) tells us that the slope of of the line between beginning and end of year test scores is related to social class. For our purposes here we need not concern ourselves with the direction of causality or why this correlation exists. All we need to know is that scores on intelligence tests are strong predictors of academic achievement. Thus, we can predict that, in general, students from higher socioeconomic backgrounds will show greater value added and these measures will be unfair to teachers who teach children who live in poverty. Overtime, this will create a disincentive for our best teachers to work with the children who most need their help.


Atlantic: The toxins that threaten our brains

12 Aug

From James Hamblin at The Atlantic, The Toxins that Threaten our Brains.”

“Forty-one million IQ points. That’s what Dr. David Bellinger determined Americans have collectively forfeited as a result of exposure to lead, mercury, and organophosphate pesticides.”

From Bellinger’s paper:

“Based on the estimated number of FSIQ (Full-Scale IQ) points lost, the population burdens associated with environmental chemical exposures of children are surprisingly large.”


Risk factors for early-onset dementia

17 Mar

A paper “Cardiovascular and cognitive fitness at age 18 and risk of early-onset dementia” in the journal Brain, reports:

 “lower cardiovascular fitness and cognitive performance in early adulthood were associated with an increased risk of early-onset dementia and mild cognitive impairment later in life, and the greatest risks were observed for individuals with a combination of low cardiovascular fitness and low cognitive performance.”

Here is a good summary in Science Daily.

As always, we must remember that correlation is not causation and we cannot directly infer from this study that exercise and better diet will prevent early-onset dementia. One website reported the study this way: “Physical Fitness During Teens Prevents Early Onset of Dementia: Study,” a claim that, while plausible, goes beyond the evidence actually reported in the study.


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James Flynn: Are we getting smarter?

25 Sep

Here is an interview with James Flynn as part of the promotion for his book Are We Getting Smarter?: Rising IQ in the Twenty-First Century. Flynn is most famous for his discovery of what is now called the Flynn Effect, the observed substantial increase in IQ scores over time.


[Full disclosure: My research is cited on page 15 of this book]

Blood vessels in eye may indicate brain health

25 Jul

The retina is the thin layer of sensory neurons that line the back of the inside of the eye ball.


These sensory neurons are photoreceptors that convert photons to nerve signals and are the basis for our ability to see. In embryonic development the retina originates in the brain and migrates to the eye. It maintains connection to the brain via the optic never.

The close connection between the brain and the retina has led some to speculate that the retina might give indications about the health of the brain. If true, this could have important clinical consequences since, unlike the brain, the retina can be examined by looking though the eye.

A study published in the most recent issue of the journal Psychological Science has found evidence to support this speculation. The researches found correlations between the caliber of retinal blood vessels and psychological function. Wide venules (small blood vessels that carry blood back to the heart) were associated with poorer cognitive performance.

This research suggest that it may be possible to assess the circulatory health of the brain through an non-invasive technique. The authors point out:

“The findings indicate that retinal venular caliber may be an indicator of neuropsychological health years before the onset of dementing diseases and suggest that digital retinal imaging may be a useful investigative tool for psychological science.”

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