Tag Archives: Intelligence

Do your siblings lower your IQ?

7 Jun

As the number of siblings increases, the fraction of parental resources received by each one declines. Thus, it has been suggested that larger sib size should be associated with lower IQ and lower school performance. A recent paper in the journal Intelligence looked at the evidence. Here is the abstract:

We examine the effects of child sibship size on intelligence, school performance and adult income for a sample of Swedish school children (n = 1326). These children were measured in grade three in 1965 (age 10) and in grades six (age 13) and nine (age 16), and the women and men were later followed up in adulthood at ages 43 and 47, respectively. Using Bayesian varying-intercept modeling we account for differences between school classes in each of our three response variables: IQ-scores, school grades and adult income, and control for background variables such as gender, socioeconomic status, and maternal- and paternal age. Consistent with previous research, we find patterns of decreasing IQ scores for increasing sibship sizes, specifically for an increasing number of older siblings. No relationships between sibship size and children’s school grades are found. We find, however, patterns of decreasing adult income for an increasing number of younger siblings. In addition, considerable amounts of variations in intelligence scores as well as school grades are found between school classes. Some implications of the findings and suggestions for future research are provided.

James Flynn on the Flynn Effect

24 Oct

I showed this video to my doctoral students last week. It’s a nice summary of Flynn’s work. I regard the Flynn Effect as one of the most important discoveries, a greatest mysteries, of scientific psychology.

Special brag point: I am the author of the study he mentions on Ohio school examinations.

Are our brains getting bigger?

17 Feb

A paper in Learning and Individual Differences:

“Secular increases in brain mass over nearly a century have been noted for both males and females in the UK and Germany. It has been argued that such trends may be associated with the Flynn effect. The IQ gain predicted on the basis of these trends is 0.19 and 0.08 points per decade for UK, and 0.2 and 0.15 points per decade for German males and females respectively, indicating a small contribution to the Fullscale IQ trends in these countries (2.95% of the German decadal gain and 12.73% of the UK gain). There is also a sex difference in the rates of brain mass gain in both countries, favoring males. Temporal correlations between the secular trend in UK brain mass and European Flynn effects on Fullscale IQ, Crystallized, Fluid and Spatial abilities reveal correlations ranging from 0.751 in the case of Fluid ability to 0.761 in the case of Crystallized ability. The brain mass increase may be an imperfect proxy for changes in specific neuroanatomical structures important for IQ gains. Its small contribution to these gains is also consistent with the influence of other contributing factors. Increasing brain mass is predicted by the life history model of the Flynn effect as it suggests increased somatic effort allocation into bioenergetically expensive cortical real estate facilitating the development of specialized cognitive abilities.”


Not genes versus environment

20 Dec

Most people think that the question is nature versus nurture. The reality is much much complex and much more interesting.

The current issue of The Observer, a publication of the Association for Psychological Science, includes the following quiz:

  1. Cognitive ability in the industrialized world “is approximately 50% to 70% heritable,” reports the Tucker-Drob team. This means that
    1. 50% to 70% of one’s cognitive ability is attributable to one’s genes.
    2. 50% to 70% of the variation among individuals is attributable to their genes.
  2. The genetic influence on intelligence scores (heritability) is greatest
    1. early in life (for example, at age 3), before varied experiences diverge our life courses.
    2. later in life (for example, at age 50 and beyond).
  3. The genetic influence on intelligence scores is greatest among those
    1. at lower socioeconomic levels.
    2. at higher socioeconomic levels.
  4. Increasing the quality and availability of educational opportunity serves to
    1. decrease the genetic influence on intelligence scores.
    2. Increase the genetic influence on intelligence scores.

You can find the answers here. For a deeper discussion see the original paper.

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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]

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