Tag Archives: Intelligence quotient

tDCS, reason to reserve judgement

6 May

Many of the articles I read on transcranial direct current stimulation follow a similar pattern. The intrepid reporter is strapped with electrodes to the skull and, after reporting a tingling feeling, describes some cognitive benefit from the procedure.

A good piece by Kira Peikoff in The New York Times breaks that pattern and acknowledges the limits of our knowledge about tDCS:

“In January, the journal Brain Stimulation published the largest meta-analysis of tDCS to date. After examining every finding replicated by at least two research groups, leading to 59 analyses, the authors reported that one session of tDCS failed to show any significant benefit for users.”



“Cognitive Abilities Across the Life Span”

2 Apr

An important paper published in Psychological Science: “When Does Cognitive Functioning Peak? The Asynchronous Rise and Fall of Different Cognitive Abilities Across the Life Span” Here is the abstract (emphasis added):

“Understanding how and when cognitive change occurs over the life span is a prerequisite for understanding normal and abnormal development and aging. Most studies of cognitive change are constrained, however, in their ability to detect subtle, but theoretically informative life-span changes, as they rely on either comparing broad age groups or sparse sampling across the age range. Here, we present convergent evidence from 48,537 online participants and a comprehensive analysis of normative data from standardized IQ and memory tests. Our results reveal considerable heterogeneity in when cognitive abilities peak: Some abilities peak and begin to decline around high school graduation; some abilities plateau in early adulthood, beginning to decline in subjects’ 30s; and still others do not peak until subjects reach their 40s or later. These findings motivate a nuanced theory of maturation and age-related decline, in which multiple, dissociable factors differentially affect different domains of cognition.”

Definitely look at Figure 1 in the pdf.

IQ and Alcohol Consumption

1 Mar

A paper published in Alcoholism: Clinical and Experimental Research:

Studies of the association between IQ and alcohol consumption have shown conflicting results. The aim of this study was to investigate the association between IQ test results and alcohol consumption, measured as both total alcohol intake and pattern of alcohol use.

The study population consists of 49,321 Swedish males born 1949 to 1951 who were conscripted for Swedish military service 1969 to 1970. IQ test results were available from tests performed at conscription. Questionnaires performed at conscription provided data on total alcohol intake (consumed grams of alcohol/wk) and pattern of drinking. Multinomial and binomial logistic regressions were performed on the cross-sectional data to estimate odds ratios (ORs) with 95% confidence intervals (CIs). Adjustments were made for socioeconomic position as a child, psychiatric symptoms and emotional stability, and father’s alcohol habits.

We found an increased OR of 1.20 (1.17 to 1.23) for every step decrease on the stanine scale to be a high consumer versus a light consumer of alcohol. For binge drinking, an increased OR of 1.09 (95% CI = 1.08 to 1.11) was estimated for every step decrease on the stanine scale. Adjustment for confounders attenuated the associations. Also, IQ in adolescence was found to be inversely associated with moderate/high alcohol consumption measured in middle age.

We found that lower results on IQ tests are associated with higher consumption of alcohol measured in terms of both total alcohol intake and binge drinking in Swedish adolescent men.”

Ironically the account of this study in The Telegraph linked to this story:

Starbucks to offer wine and beer in evenings

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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