108 Chapter 4drawers. Thus the published studies represent
a biased sample of the studies that have been
conducted. More recent meta-analyses have
ways of addressing the file-drawer problem,
either by reporting the number of studies in
file drawers that would be needed to negate
the results or by making attempts to include
unpublished studies in the meta-analysis. The
file-drawer problem may not be as significant
in studies of sex comparisons as in other re-
search because some of the sex comparison
data come from studies whose primary pur-
pose was not to evaluate sex. Investigators
may be studying aggression, empathy, or
math ability for other reasons aside from sex
but report the results of sex comparisons as a
matter of routine.
There have been so many sex compari-
son meta-analyses published in the 1980s and
1990s that Janet Hyde (2005a) published a
paper called “The Gender Similarities
Hypothesis,” in which she reviewed the results
of 46 meta-analyses, many of which are dis-
cussed in this chapter. She concluded that 30%
of the effects were in the close to zero range
(d< .10) and that 48% were small (d< .35).
She noted three exceptions—large effect
sizes in throwing velocity (males faster than
females), attitudes toward sex (males more
liberal than females), and physical aggression
(males greater than females). Let’s see what
some of the meta-analyses have to say.TAKE HOME POINTS
■ Men and women are more similar than different, as
shown by the overlapping distributions in Figure 4.1.
■ The first comprehensive review of sex differences was
published by Maccoby and Jacklin and revealed that
there were sex differences in only four domains: verbal,
spatial, math, aggression.■ That review was a narrative review, which is limited by
the fact that it doesn’t take into consideration the size
of the differences.
■ Meta-analysis provides a way to quantitatively review
studies, taking into consideration sample size and
effect sizes ( ds).
■ Meta-analysis also allows one to consider whether cer-
tain variables, known as moderator variables, influence
the size of the sex difference.
■ A disadvantage of both narrative and meta-analytic
reviews is that studies finding no differences are less
likely to be published, a weakness known as the file-
drawer problem.Sex Comparisons in Cognitive Abilities
Many people assume men have greater spa-
tial and math abilities than women. People
also assume women have greater verbal skills
than men. As the literature here shows, these
statements are overly simplistic. This area of
research is highly controversial because a sex
difference in an area of cognition could lead
people to assume one sex is more suitable for
a career requiring that ability. This could ul-
timately lead to sex discrimination. Thus it is
important that we evaluate this research care-
fully. For each cognitive ability I discuss, one
or more meta-analyses exist. I report the effect
size, thed, in parentheses for the major find-
ings. To be consistent throughout the chapter,
adthat is positive will indicate men outper-
form women, and adthat is negative will indi-
cate women outperform men (see Figure 4.3).Spatial Ability
Spatial skills involve the ability to think
about and reason using mental pictures
rather than words. However, spatial ability isM04_HELG0185_04_SE_C04.indd 108 6/21/11 8:02 AM