INTRODUCTION TO SEX DIFFERENCES IN INTELLIGENCE ✏ SPA2 LECTURE 4

Sex differences in General Intelligence

  • Interest in gender differences in abilities and behaviours started in 1880s
  • Scientists believed men were superior in mental abilities because of women’s smaller brains.
  • Research methodology involves quantifying group differences
    • Effect sizes
    • Meta-analysis

Effect sizes

  • These show how important the difference is. Most common is Cohen’s d:
    • 0.2 effect size is small
    • 0.5 effect size is medium
    • 0.8 effect size is large
      • Note: positive effect sizes denote higher average among males compared to females throughout the rest of the lecture.


Meta-analyses

  • Single experiments may be limited in sample size.
  • Meta-analysis uses results from numerous studies to calculate an average effect size.
  • Potentially more meaningful - bigger sample / range of participants.

Sex differences across the lifespan

Lynn and Irwing (2004); Irwing and Lynn (2005)

  • Collected data from 57 studies = 80,000 participants
  • Findings:
    • <15 years = no sex differences
      • d=0.02
    • 15-19 years = men scoring 2 points higher
      • d=0.16
    • Undergrads = men scoring 3-5 points higher
      • d=0.22-0.33
    • Adults = men score 5 points higher
      • d=0.30

Sex differences in Spatial Ability

Linn & Petersen (1985); McNulty (2007)

  • Average effect size: d=0.51, 18 studies
    • Mental rotation: d=0.66, 81 studies
    • Other spatial tasks: d=0.19-0.95, 62 studies
  • Suggests a medium effect size in favour of males.

Sex differences in Mathematical Ability

Else-Quest et al., (2010)

  • Maths: d=0.11, number of studies = 40
  • Spatial: d=0.15, number of studies = 40
  • Maths motivation: d=0.22, number of studies = 41
  • Maths anxiety: d= -0.28, number of studies = 41

Verbal abilities

In most cases, effect size is less than small to virtually non-existent.

Hedges & Nowell (1995)
Adolescents --> Vocabulary = +0.60
Adolescents --> Reading comprehension = -0.09

Hyde & Linn (1988)
Children & Adults --> Quality of Speech = -0.33
Children & Adults --> Reading comprehension = -0.03
Children & Adults --> Vocabulary = -0.02

Feingold (1988)
Adolescents --> Verbal reasoning = -0.02
Adolescents --> Language = -0.40

Summary of Sex Differences

  • Small effect size in favour of men in general IQ
  • Medium effect size in favour of men in spatial intelligence
  • Small effect size in favour of men in mathematical ability
  • No real evidence favouring women in verbal intelligence

Why might these sex differences exist?

Nature/biology

  • Are men predisposed to be better at spatial abilities and mathematical tasks?

Nature/environment

  • Are men better at spatial ability and mathematical tasks because of environmental influences/access to more opportunities to develop these abilities?

Biological Explanations

Brain size and structure:

Brain size

  • Men’s brains are on average 10% larger than women’s.
  • This difference is only seen from adolescence onwards due to different rates of maturity.
  • Link is small and has been an overused explanation.

Brain structure

  • Tasks are solved more efficiently when carried out by one side of the brain.
  • Allen et al., (1991) females have a bigger Splenium.
  • Bit of the brain that connects the two hemispheres.
  • More likely to engage in tasks using both sides of the brain (a slightly less efficient way of doing it)
  • Males using their brain more efficiently?

Brain functioning

  • White matter (information transmission) versus Grey matter (information processing)



    Haier et al., (2005)

  • Used MRI to find areas of the brain relating to intelligence.

Findings

  • IQ among women were related to more white matter areas and fewer grey matter areas than men.

Conclusions

  • Males and females can achieve the same IQ scores using different parts of the brain.
  • Intelligence in men might be more related to information processing - grey matter (e.g. spatial ability)

Hormones
Testosterone

  • Male sex hormone responsible for growth and development of male genitalia in womb and during adolescence.

Oestrogen

  • Produced mostly by the ovaries, responsible for female secondary sex characteristics.

Why do these matter?

  • Testosterone has been found to be related to higher performance in spatial ability tasks.

Hormonal Evidence

Choi & Silverman (1996)

  • Looked at how males and females provided directions.
  • Women gave relative directions and landmarks
  • Men gave distance and cardinal directions

Findings

  • Among men, testosterone was positively related to using distance and cardinal directions.

Barry et al. (2013)

  • Women with polycystic ovary syndrome have elevated levels of testosterone.

Findings

  • PCOS participants scored significantly higher than controls on a 3D mental rotation task.

Evolutionary Explanations

  • Men need spatial ability when:
    • Forging and gathering food
    • Engaging in warfare with others
    • Maximising reproductive success

Jones et al. (2003)

  • Males with greater spatial ability, more likely to win wars, more able to supply food and maintain more relationships, more attractive to women, more offspring with ‘spatial ability genes’.
  • BUT...Consider the circularity argument:
    • Which came first: hunting or spatial abilities?

Environmental Explanations

Hoffman et al., (2012)

  • Examined spatial ability in two genetically related tribes but different environments.
  • One was a matrilineal society and one was a patrilineal society.
  • If we accept only biological explanations, we would expect to see no differences in spatial ability.
  • But this is not what they found…
  • Suggests an environmental role?

Stereotypes

  • Stereotypes can be a central influence.
  • Stereotypes about how we should behave and about how others should behave.
  • Boys tend to play with toys that encourage development of spatial awareness skills.
  • Campbell et al., (2000) toy preference reflects gender stereotypes in children as young as 9 months old.
  • Boys tend to be drawn to toys testing spatial ability - e.g. Lego, building blocks etc.

Feng et al., (2007)

  • Spatial attention and mental rotation among gamers/non-gamers and males/females.

Experiment 1:

  • Gamers performed better than non-gamers.
  • No sex difference in gamers group.
  • Among non-gamers, males performed better than females.

Experiment 2:

  • Experimental group: 10 hour action video game training.
  • Control group: 10 hour non-action game training
  • All those in the experimental group improved in ability
  • Females benefitted from the training more than males.
  • In the experimental group, no sex differences after training.
  • In the control group, males performed better both pre and post training.

Where do these preferences come from?


Influence of parents/carers:


Reinforcement:

  • Langlois & Down (1980)
  • Mothers and fathers reinforce sex appropriate behaviour and discourage sex inappropriate behaviour.

Modelling:

  • Children observe same sex others and gain stereotypes on how they ‘should’ behave (e.g. what toys to play with).
  • Forms part of their gender identity.

Socialisation of boys


Entwistle et al., (1994)

  • Boys given greater freedom to explore.

Toys and Stereotypes

  • BBC No More Boys and Girls: Can Our Kids Go Gender Free?
    Seavy, Katz and Zalk (1975)
    • Participants chose toys associated with stereotypical views of gender.
      Sidorowicz & Lunney (1980)
  • Dressed babies in different gender-stereotypical clothes.
    • BOY: 50% male and 80% female chose football for them to play with.
    • GIRL: 88.8% male & 72.7% female chose a doll for them to play with.

Stereotypes in Education

  • STEM subjects:
    • Girls are less likely to choose these subjects - stereotyped as ‘masculine subjects’.
    • Therefore less likely to develop spatial ability skills and mathematical ability skills.
      • Institute of Physics: Girls make up 20% of those taking A-Level Physics.

Moss-Racusin et al., (2012)

  • Applications for Lab Manager in STEM subjects were randomly given a male or a female name.
  • Findings: Faculty rated male applicant as more competent and hireable than when then female name was used (even though the applications were identical)

Stereotype Threats

Negative stereotypes about different social groups can affect ability.


Spencer et al., (1999)

  • 2 conditions:
    • Male and female took a maths test
    • Male and female took a maths test but told that males had scored better on this test in the past.
  • Findings:
    • Females in 2nd condition scored lower than men (no difference in condition 1)

Presence of others

Inzlicht & Ben-Zeev (2000)

  • Participants took maths and verbal tests.
  • 2 conditions for each:
    • Female participants with two other females (same sex)
    • Female participants with two males (minority)

Gender Inequality

  • Global Gender Gap (GGI: Global Gender Index) by the World Economic Forum
  • Nations with greater gender equality portray smaller gender differences in Mathematical performance.
  • The paler the colour of the country, the more equal the genders are.

Caution of Generalisations

  • Female mathematicians e.g. Marie-Sophie Germain (French, 1776-1831), Emmy Noether (German, 1882-1935), Maryam Mirzakhani (Professor at Stanford University)
  • Females: top scorers on the International Mathematics Olympiad
    • Difficult competition in mathematical solving
    • Top scorers: exceptional (1-in-a-million level) skills
    • An increase in the number of female participants with time.

Psycho-biosocial model

The psychobiosocial model is based on the idea that some variables are both biological and social and, therefore, cannot be classified into one of these two dichotomous categories.