Mill on patterns of human existence

“… it is important to give the freest scope possible to uncustomary things, in order that it may in time appear which of these are fit to be converted into customs. But independence of action, and disregard of custom are not solely deserving of encouragement for the chance they afford that better modes of action, and customs more worthy of general adoption, may be struck out; nor is it only persons of decided mental superiority who have a just claim to carry on their lives in their own way. There is no reason that all human existences should be constructed on some one, or some small number of patterns. If a person possesses any tolerable amount of common sense and experience, his own mode of laying out his existence is the best, not because it is the best in itself, but because it is his own mode. Human beings are not like sheep; and even sheep are not undistinguishably alike.”
—J. S. Mill, On Liberty

Profiles of intelligence

Johnson, W. & Bouchard, Jr., T. J. Sex Differences in Mental Abilities: g Masks the Dimensions on Which They Lie. Intelligence, 2007, 35, 23-39:

“… we have presented evidence supporting the idealized notion of general intelligence as a general-purpose mechanism that accesses a toolbox made up of components that vary from individual to individual. Though everyone clearly has most if not all of the same tools, individuals appear to differ not only in the skill with which they use their tools, but also in the specific tools they habitually use. For some of the more specific tools, it would appear that using one tool means failing to use another. […] Performance on image rotation tasks is known to predict success in fields such as airplane piloting, engineering, physical sciences, and fine arts better than does general intelligence, and especially verbal ability. What has perhaps not been recognized is that inclusion of verbal ability in assessments used to recruit individuals to those fields may actually act to impair efforts to select those with the talents most relevant to the jobs in question.”

John Raven often quotes Spearman:

“Every normal man, woman and child is a genius at something … the problem is to identify at what … this must be a most difficult task because it occurs in only a minute proportion of circumstances … this cannot be done with any of the procedures in current use …”

(And Raven would still quite like to know how to fix psychometrics.)

"... we have presented evidence supporting the idealized notion of
general intelligence as a general-purpose mechanism that accesses a
toolbox made up of components that vary from individual to individual.
Though everyone clearly has most if not all of the same tools,
individuals appear to differ not only in the skill with which they use
their tools, but also in the specific tools they habitually use. For
some of the more specific tools, it would appear that using one tool
means failing to use another. [...] Performance on image rotation tasks
is known to predict success in fields such as airplane piloting,
engineering, physical sciences, and fine arts better than does general
intelligence, and especially verbal ability. What has perhaps not been
recognized is that inclusion of verbal ability in assessments used to
recruit individuals to those fields may actually act to impair efforts
to select those with the talents most relevant to the jobs in question."

Individual differences (continued)

“I am surprised that the author has used this data set. In my lab, when we collect data with such large individual differences, we refer to the data as ‘junk’. We then redesign our stimuli and/or experimental procedures, and run a new experiment. The junk data never appear in publications”

—An anonymous reviewer in 2005, commenting on research that sought to model individual differences in cognition.

From the intro to Navarro, D. J.; Griffiths, T. L.; Steyvers, M. & Lee, M. D. Modeling individual differences using Dirichlet processes. Journal of Mathematical Psychology, 2006, 50, 101-122

Gender differences in psychology

My take on this:

  1. There are gender differences in ability, but not many, and the effect size is typically small* (Hyde 2005).
  2. Brain structure development is affected by a range of factors, environmental and genetic. For instance brain structure changes as a result of learning (e.g., Maguire et al, 2000). (And the phrase “hard-wired” is annoying.)
  3. A mean difference between groups, mean(group 1) > mean(group 2), on some measure does not imply that everyone in group 1 is better than everyone in group 2. So when selecting someone for a job, say, you could (a) grab a load of people with the gender which, on average, has (very slightly—see point 1) more of the ability you want and choose someone at random, or (b) you could choose someone who has more of the ability you want, and not focus on what gender they happen to be.
  4. The designers of IQ tests hack their tests to remove gender differences, for instance the designers of the British Ability Scales (version 2) “used three strategies to test for fairness and to remove items likely to increase bias” (Hill, 2005). Blinkhorn (2005) says: “Where there are sex differences to be found, detailed study of the internal workings of the test tends to show why. That’s not based on instinct, but on my professional experience in designing gender-fair tests.”

Blinkhorn, S. (2005). Intelligence: a gender bender. Nature, 438, 31-32.

Hill, V. (2005). Through the Past Darkly: A Review of the British Ability Scales. Second Edition. Child and Adolescent Mental Health, 10, 87-98.

Hyde, J. S. (2005). The gender similarities hypothesis. American Psychologist, 60, 581-592.

Maguire, E. A.; Gadian, D. G.; Johnsrude, I. S.; Good, C. D.; Ashburner, J.; Frackowiak, R. S. & Frith, C. D. (2000). Navigation-related structural change in the hippocampi of taxi drivers. Proceedings of the National Academy of Sciences of the United States of America, 97, 4398-4403

* Cis women are better at giving birth than cis men, with a large effect size.