Perils and pitfalls of reporting sex differences

Abstract

The idea of sex differences in the brain both fascinates and inflames the public. As a result, the communication and public discussion of new findings is particularly vulnerable to logical leaps and pseudoscience. A new US National Institutes of Health policy to consider both sexes in almost all preclinical research will increase the number of reported sex differences and thus the risk that research in this important area will be misinterpreted and misrepresented. In this article, I consider ways in which we might reduce that risk, for example, by (i) employing statistical tests that reveal the extent to which sex explains variation, rather than whether or not the sexes 'differ', (ii) properly characterizing the frequency distributions of scores or dependent measures, which nearly always overlap, and (iii) avoiding speculative functional or evolutionary explanations for sex-based variation, which usually invoke logical fallacies and perpetuate sex stereotypes. Ultimately, the factor of sex should be viewed as an imperfect, temporary proxy for yet-unknown factors, such as hormones or sex-linked genes, that explain variation better than sex. As scientists, we should be interested in discovering and understanding the true sources of variation, which will be more informative in the development of clinical treatments.

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Opinion piece
Cite this article: Maney DL. 2016 Perils and
pitfalls of reporting sex differences. Phil.
Trans. R. Soc. B 371: 20150119.
http://dx.doi.org/10.1098/rstb.2015.0119
Accepted: 15 November 2015
One contribution of 16 to a theme issue
‘Multifaceted origins of sex differences in the
brain’.
Subject Areas:
behaviour, neuroscience
Keywords:
gender differences, male, female,
sex differences in the brain,
US National Institutes of Health policy
Author for correspondence:
Donna L. Maney
e-mail: dmaney@emory.edu
Electronic supplementary material is available
at http://dx.doi.org/10.1098/rstb.2015.0119 or
via http://rstb.royalsocietypublishing.org.
Perils and pitfalls of reporting
sex differences
Donna L. Maney
Department of Psychology, Emory University, Atlanta, GA 30322, USA
The idea of sex differences in the brain both fascinates and inflames the public.
As a result, the communication and public discussion of new findings is par-
ticularly vulnerable to logical leaps and pseudoscience. A new US National
Institutes of Health policy to consider both sexes in almost all preclinical
research will increase the number of reported sex differences and thus the
risk that research in this important area will be misinterpreted and misrepre-
sented. In this article, I consider ways in which we might reduce that risk,
for example, by (i) employing statistical tests that reveal the extent to which
sex explains variation, rather than whether or not the sexes ‘differ’, (ii) properly
characterizing the frequency distributions of scores or dependent measures,
which nearly always overlap, and (iii) avoiding speculative functional orevol-
utionary explanations for sex-based variation, which usually invoke logical
fallacies and perpetuate sex stereotypes. Ultimately, the factor of sex should
be viewed as an imperfect, temporary proxy for yet-unknown factors, such
as hormones or sex-linked genes, that explain variation better than sex. As
scientists, we should be interested in discovering and understanding the
true sources of variation, which will be more informative in the development
of clinical treatments.
1. Introduction
Sex differences in the brain have made headlines for more than a century. In
1912, James Crichton-Browne, a prominent neuropsychologist and collaborator
of Darwin, explained in a New York Times article why ‘women think quickly’
and ‘men are originators’:
In woman, Sir James said, the posterior region of the brain receives a richer flow of
arterial blood, in men the anterior region. The work of the two regions of the brain
is different. The posterior region is mainly sensory and concerned with seeing and
hearing. The anterior region includes the speech centre, the higher inhibitory centres,
which are concerned with will, and the association centres, concerned with appetites
and desires based upon internal sensations.
There is, Sir James thinks, a correspondence between the richer blood supply of the
posterior region of the brain in women and their delicate powers of sensuous percep-
tion, rapidity of thought and emotional sensibility, and between the richer blood
supply of the anterior region in men and their greater originality on higher levels
of intellectual work, their calmer judgment and their stronger will [1, p. 4].
Although we may find such revelations archaic and even a bit offensive, the same
type of thinking remains prevalent today. News reports and information-based
websites such as Wikipedia, WedMD and HowStuffWorks.com contain an alarm-
ing amount of pseudoscience. It is commonly asserted, for example, that women
listen with both sides of the brain, whereas men use only the left side [2,3] and
that women use white matter to think, whereas men use grey [4,5]. Women alleg-
edly have 10 times as much white matter as do men, whereas men have 6.5 times
as much grey matter as dowomen ([6,7], reviewed in [8]). Whereas women navigate
using cerebral cortex, men use ‘an entirely different area’ that is ‘not activated in
women’s brains’ [6]. Such assertions, although inaccurate, are easy to find on the
Internet and in the popular press.
The misrepresentation of sex differences is likely to become even more com-
monplace. Partly because of increasing availability of imaging technologies, the
percentage of journal articles that refer to sex differences and the brain has more
than doubled in the past two decades ( figure 1a). Over the same period, media
&2016 The Author(s) Published by the Royal Society. All rights reserved.