Albert-Laszlo Barabasi is a physicist and network scientist who int...
An important finding from this paper, "This suggests the productivi...
Always be careful when evaluating proportions without controlling f...
This access to the full publishing career data was key to their dis...
SOCIAL SCIENCES
Historical comparison of gender inequality in scientific
careers across countries and disciplines
Junming Huang
a,b,c,1
, Alexander J. Gates
a,1
, Roberta Sinatra
d,e
, and Albert-L
´
aszl
´
o Barab
´
asi
a,f,g,h,2
a
Network Science Institute and Department of Physics, Northeastern University, Boston, MA 02115;
b
CompleX Lab, School of Computer Science and
Engineering, University of Electronic Science and Technology of China, Chengdu 611731, China;
c
Paul and Marcia Wythes Center on Contemporary China,
Princeton University, Princeton, NJ 08540;
d
Department of Computer Science, IT University of Copenhagen, 2300 Copenhagen, Denmark;
e
ISI Foundation,
10126 Turin, Italy;
f
Channing Division of Network Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115;
g
Department of
Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA 02115; and
h
Department of Network and Data Science, Central European
University, 1051 Budapest, Hungary
Edited by Susan T. Fiske, Princeton University, Princeton, NJ, and approved January 22, 2020 (received for review August 15, 2019)
There is extensive, yet fragmented, evidence of gender differ-
ences in academia suggesting that women are underrepresented
in most scientific disciplines and publish fewer articles through-
out a career, and their work acquires fewer citations. Here, we
offer a comprehensive picture of longitudinal gender differences in
performance through a bibliometric analysis of academic publish-
ing careers by reconstructing the complete publication history of
over 1.5 million gender-identified authors whose publishing career
ended between 1955 and 2010, covering 83 countries and 13 dis-
ciplines. We find that, paradoxically, the increase of participation
of women in science over the past 60 years was accompanied by
an increase of gender differences in both productivity and impact.
Most surprisingly, though, we uncover two gender invariants, find-
ing that men and women publish at a comparable annual rate
and have equivalent career-wise impact for the same size body of
work. Finally, we demonstrate that differences in publishing career
lengths and dropout rates explain a large portion of the reported
career-wise differences in productivity and impact, although pro-
ductivity differences still remain. This comprehensive picture of
gender inequality in academia can help rephrase the conversation
around the sustainability of women’s careers in academia, with
important consequences for institutions and policy makers.
gender inequality | science of science | STEM | scientific careers
G
ender differences in academia, captured by disparities in
the number of female and male authors, their productiv-
ity, citations, recognition, and salary, are well documented across
all disciplines and countries (1–8). The epitome of gender differ-
ence is the “productivity puzzle” (9–13)—the persistent evidence
that men publish more than women over the course of their
career, which has inspired a plethora of possible explanations
(14–16), from differences in family responsibilities (17–19), to
career absences (20), resource allocation (21), the role of peer
review (22), collaboration (23, 24), role stereotypes (25), aca-
demic rank (26), specialization (27), and work climate (28).
The persistence of these gender differences could perpetuate
the naive interpretation that the research programs of female
and male scientists are not equivalent. However, such simplistic
reading of the data dismisses increasing evidence that systemic
barriers impede the female academic. Indeed, the deep interre-
latedness of these factors has limited our ability to differentiate
the causes from the consequences of the productivity puzzle,
complicating the scientific community’s ability to enact effective
policies to address it.
A key methodological obstacle has been the difficulty to recon-
struct full publishing careers for scientists of both genders across
the diverse academic population. Consequently, much of the
available evidence on gender differences is based on case stud-
ies limited to subsets of active scientists in specific countries,
disciplines, or institutions, making it difficult to compare and
generalize the finding to all of science. A further complication
arises from the heavy-tailed nature of academia: a dispropor-
tionately small number of authors produce a large fraction of
the publications and receive the majority of the citations (29),
an effect that is exacerbated in small sample sizes (30). To truly
understand the roots of the gender inequality, we need to survey
the whole longitudinal, disciplinary, and geographical landscape,
which is possible only if we capture complete publishing careers
for all scientists across disciplinary and national boundaries.
Here, we reconstructed the full publishing career of 7,863,861
scientists from their publication record in the Web of Sci-
ence (WoS) database between 1900 and 2016. By deploying a
state-of-the-art method for gender identification (SI Appendix,
section S2.E), we identified the gender of over 3 million authors
(856,889 female and 2,146,926 male) spanning 83 countries
and 13 major disciplines (SI Appendix, section S2). We then
focused on 1,523,002 scientists (412,808 female and 1,110,194
male) whose publishing careers ended between 1955 and 2010
(SI Appendix, sections S1 and S2.H), allowing us to systemati-
cally compare complete male and female careers. This extensive
sample covers 33% of all papers published between 1955 and
2010 but due to methodological limitations, systematically lacks
Significance
Empirical evidence suggests significant gender differences in
the total productivity and impact of academic careers across
science, technology, engineering, and mathematics (STEM)
fields. Paradoxically, the increase in the number of women
academics over the past 60 years has increased these gen-
der differences. Yet, we find that men and women publish a
comparable number of papers per year and have equivalent
career-wise impact for the same total number of publications.
This suggests the productivity and impact of gender differ-
ences are explained by different publishing career lengths
and dropout rates. This comprehensive picture of gender
inequality in academic publishing can help rephrase the con-
versation around the sustainability of women’s careers in
academia, with important consequences for institutions and
policy makers.
Author contributions: J.H., A.J.G., R.S., and A.-L.B. designed research; J.H. and A.J.G. per-
formed research; J.H. and A.J.G. analyzed data; and J.H., A.J.G., R.S., and A.-L.B. wrote
the paper.y
Competing interest statement: A.-L.B. is founder of Nomix, Foodome, and Scipher
Medicine, companies that explore the role of networks in health. All other authors
declare no competing interest.y
This article is a PNAS Direct Submission.y
This open access article is distributed under Creative Commons Attribution License 4.0
(CC BY).y
See online for related content such as Commentaries.y
1
J.H. and A.J.G. contributed equally to this work.y
2
To whom correspondence may be addressed. Email: A.Barabasi@northeastern.edu.y
This article contains supporting information online at https://www.pnas.org/lookup/suppl/
doi:10.1073/pnas.1914221117/-/DCSupplemental.y
First published February 18, 2020.
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AB
C
D
Fig. 1. Gender imbalance since 1955. (A) The number of active female (orange) and male (blue) authors over time and the total proportions of authors
(Inset). (B and C) The proportion of female authors in several disciplines (B) and countries (C); for the full list, see SI Appendix, Tables S3 and S4. (D) The
academic publishing career of a scientist is characterized by his or her temporal publication record. For each publication, we identify the date (gold dot) and
number of citations after 10 years c
10
(gold line, lower). The aggregation by year provides the yearly productivity (light gold bars), while the aggregation
over the entire career yields the total productivity (solid yellow bar, right) and total impact (solid yellow bar, right). Career length is calculated as the time
between the first and last publication, and the annual productivity (dashed gold line) represents the average yearly productivity. Authors drop out from our
data when they published their last article.
authors from China, Japan, Korea, Brazil, Malaysia, and Singa-
pore (SI Appendix, section S2). To demonstrate the robustness
of our findings to database bias and author disambiguation
errors, we independently replicated our results in two addi-
tional datasets: the Microsoft Academic Graph (MAG) (31)
and the Digital Bibliography & Library Project (DBLP), each
using different criteria for publication inclusion and methodolo-
gies for career reconstruction (SI Appendix, sections S1 and S6).
Our focus on bibliometric data limits our analysis to publishing
careers and is unable to capture the career dynamics of teaching,
administrative, industrial, or government related research activ-
ities. Nevertheless, our efforts constitute an extensive attempt
4610 | www.pnas.org/cgi/doi/10.1073/pnas.1914221117 Huang et al.
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SOCIAL SCIENCES
to quantify gender inequality in science, technology, engineer-
ing, and mathematics (STEM) publications and citations, offer-
ing a longitudinal, career-wise perspective across national and
disciplinary boundaries.
The Increasing and Persistent Gender Gap
Across all years and disciplines, women account for 27% of
authors, a number that hides important trends: while in 1955
women represented only 12% of all active authors, that frac-
tion steadily increased over the last century, reaching 35% by
2005 (Fig. 1A). Yet, these aggregate numbers hide considerable
disciplinary differences, as the fraction of women is as low as
15% in math, physics, and computer science and reaches 33%
in psychology (Fig. 1B). We also observe significant variations by
country, finding that the proportion of female scientists can be as
low as 28% in Germany and reaches parity with 50% in Russia
(Fig. 1C).
The low proportion of women actively publishing in STEM
captures only one aspect of gender inequality. Equally important
are the persistent productivity and impact differences between
the genders (Fig. 1D). We find that while, on average, male sci-
entists publish 13.2 papers during their career, female authors
publish only 9.6, resulting in a 27% gender gap in total pro-
ductivity (Fig. 2A). The difference is particularly pronounced
among productive authors, as male authors in the top 20% pro-
ductivity bracket publish 37% more papers than female authors
(Fig. 2A). Interestingly, the gender gap disappears for median
productive authors (middle 20%) and reverses for the authors
in the bottom 20%. The gender gap in total productivity per-
sists for all disciplines and almost all countries (Fig. 2 B and
C). We also observe a large gender gap in total productivity for
the highest-ranked affiliations (Fig. 2D) (determined from the
2019 Times Higher Education World University Rankings; SI
Appendix, section S2.D).
AB C DE
FG H IJ
O
TS
NM
RQ
LK
P
Fig. 2. Gender gap in scientific publishing careers. The gender gap is quantified by the relative difference between the mean for male (blue) and female
(orange) authors. In all cases the, relative gender differences are statistically significant, as established by the two-sided t test, with P values < 10
4
, unless
otherwise stated (see SI Appendix, section S4.A for test statistics). (AE) Total productivity broken down by percentile (A), discipline (B), country (C), affiliation
rank (D), and decade (E). The gender gap in productivity has been increasing from the 1950s to the 2000s. (FJ) Total impact subdivided by percentile (F),
discipline (G), country (H), affiliation rank (I), and decade (J). (K–O) Annual productivity is nearly identical for male and female authors when subdivided by
percentile (K), discipline (L), country (M), affiliation rank (N), and decade (O). (PT) Career length broken down by percentile (P), discipline (Q), country (R),
affiliation rank (S), and decade (T).
Huang et al. PNAS | March 3, 2020 | vol. 117 | no. 9 | 4611
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A
C
DE
B
Fig. 3. Controlling for career length. (A and B) The gender gap in career length strongly correlates with the gender gap in productivity across disciplines
(Pearson correlation, 0.80) (A) and countries (Pearson correlation, 0.56) (B). A gender gap of 0.0% indicates gender equality, while negative gaps indicate the
career length or productivity is greater for male careers, and positive gaps indicate the feature is greater for female careers. (C) In a matching experiment,
equal samples are constructed by matching every female author with a male author having an identical discipline, country, and career length. (D) The
average productivity provided by the matching experiment for career length compared to the population; the gender gap is reduced from 27.4% in the
population to 7.8% in the matched samples. (E) The average impact provided by the matching experiment for career length compared to the original
unmatched sample. Where visible, error bars denote 1 SD.
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SOCIAL SCIENCES
We measure the total impact during an academic career by
the number of citations accrued 10 years after publication (c
10
)
by each paper published during a career (Fig. 1D), after remov-
ing self-citations and rescaling to account for citation inflation
(32–34) (SI Appendix, section S2.F). We find that male scientists
receive 30% more citations for their publications than female
scientists (Fig. 2F). Once again, the total impact difference is
the largest for high-impact authors and reverses for median-
and low-impact authors: male authors in the top 20% in career
impact receive 36% more citations than their female counter-
parts. The disparity in impact persists in almost all countries
and all disciplines (Fig. 1 G and H), and can be found, to a
lesser extent, across all affiliations regardless of affiliation rank
(Fig. 1I).
Paradoxically, the gradual increase in the fraction of women
in science (5) (Fig. 1A) is accompanied by a steady increase in
both the productivity and impact gender gaps (Fig. 2 E and J).
The gender gap in total productivity rose from near 10% in the
1950s to a strong bias toward male productivity (35% gap) in
the 2000s. The gender gap in total impact actually switches from
slightly more female impact in the 1950s to a 34% gap favoring
male authors in the same time frame. These observations dis-
rupt the conventional wisdom that academia can achieve gender
equality simply by increasing the number of participating female
authors.
In summary, despite recent attempts to level the playing field,
men continue to outnumber women 2 to 1 in the scientific
workforce and, on average, have more productive careers and
accumulate more impact. These results confirm, using a unified
methodology spanning most of science, previous observations in
specific disciplines and countries (2, 9, 11, 12, 16, 35–38) and sup-
port in a quantitative manner the perception that global gender
differences in academia is a universal phenomenon persisting in
every STEM discipline and in most geographic regions. More-
over, we find that the gender gaps in productivity and impact
have increased significantly over the last 60 years. The universal-
ity of the phenomenon prompts us to ask: What characteristics
of academic careers drive the observed gender-based differences
in total productivity and impact?
Annual Productivity and Career Length
As total productivity and impact over a career represent a con-
volution of annual productivity and publishing career length, to
identify the roots of the gender gap, we must separate these two
factors. Traditionally, the difficulty of reconstructing full pub-
lishing careers has limited the study of annual productivity to
a small subset of authors or to career patterns observable dur-
ing a fixed time frame (39–46). Access to the full publishing
career data allows us to decompose each author’s total productiv-
ity into his or her annual productivity and career length, defined
as the time span between a scientist’s first and last publication
(Fig. 1D and SI Appendix, section S3). We find that the annual
productivity differences between men and women are negligi-
ble: female authors publish, on average, 1.33 papers per year,
while male authors publish, on average, 1.32 papers per year,
a difference, that while statistically significant, is considerably
smaller than other gender disparities (0.9%, P value < 10
9
;
Fig. 2K). This result is observed in all countries and disciplines
(Fig. 2 L and M), and we replicated it in all three datasets (SI
Appendix, section S6). The gender difference in annual produc-
tivity is small even among the most productive authors (4% for
the top 20%) and is reversed for authors of median and low
productivity.
The average annual productivity of scientists has slightly
decreased over time; yet, there is consistently no fundamental
difference between the genders (Fig. 2O). In other words, when
it comes to the number of publications per year, female and male
authors are largely indistinguishable, representing the first gen-
der invariant quantity in performance metrics. As we show next,
this invariant, our key result, helps us probe the possible roots of
the observed gender gaps.
The comparable annual productivity of male and female scien-
tists suggests that the large gender gap in total career productivity
is determined by differences in career length. To test if this is
the case, we measured the career length (Fig. 1D) of each sci-
entist in the database, finding that, on average, male authors
reach an academic age of 11.0 years before ceasing to pub-
lish, while the average terminal academic age of female authors
is only 9.3 years (Fig. 2P). This gap persists when authors
are grouped by either discipline, country, or affiliation (Fig. 2
Q, R, and S) and has been increasing over the past 60 years
(Fig. 2T). Taken together, Fig. 2 K and T suggests that a sig-
nificant fraction of the variation in total productivity is rooted
in variations in career lengths. This conclusion is supported by a
strong correlation between the career-length gap and the career-
wise productivity gap when we subdivide scientists by discipline
(Fig. 3A; Pearson correlation, 0.80) and country (Fig. 3B; Pear-
son correlation, 0.58). In other words, this strong correlation
implies that disciplines or countries with a large gender differ-
ence in the career length also have a large gender difference
in total productivity, while those disciplines or countries with
small gender differences in the career length also have a small
gender difference in total productivity. For example, the gen-
der gap in career length is smallest in applied physics (2.6%),
as so is the gender gap in total productivity (7.8%). In con-
trast, in biology and chemistry, men have 19.2% longer careers
on average, resulting in a total productivity gender gap that
exceeds 35.1%.
Given the largely indistinguishable annual productivity pat-
terns, we next ask how much of the total productivity and the
total impact gender gaps observed above (Fig. 2 A and F) could
be explained by the variation in career length. For this, we per-
form a matching experiment designed to eliminate the gender
gaps in career length. In the first population, for each female
scientist, we select a male scientist from the same discipline
(Fig. 3C and SI Appendix, section S4.B). We then constructed
a second matched population, as a subset of the first, in which
each female scientist is matched to a male scientist from the
same discipline and with exactly the same career length. In these
career length-matched samples, the gender gap in total produc-
tivity reduces from 31.0 to 7.8% (Fig. 3D). Furthermore, the
gender gap in the total impact is also reduced from 38.4 to 12.0%
(Fig. 3E). By matching pairs of authors based on observable
confounding variables, such as their discipline, we mitigate the
influence of these variables on the gender gaps. More strenuous
matching criteria controlling for country and affiliation rank do
not greatly affect these results, although they limit us to much
smaller matched populations (SI Appendix, section S4.B and Fig.
S1). While matching cannot rule out that gender differences are
influenced by unmatched variables that are unobserved here,
the significant decrease in the productivity and impact gender
gaps when we control for career length suggests that publication
career length is a significant correlate of gender differences in
academia.
To address the factors governing the end of a publishing
career, we calculated the dropout rate, defined as the yearly
fraction of authors in the population who have just published
their last paper (42, 47). We find that, on average, 9.0% of
active male scientists stop publishing each year, while the yearly
dropout rate for women is nearly 10.8% (Fig. 4A). In other
words, each year, women scientists have a 19.5% higher risk
to leave academia than male scientists, giving male authors a
major cumulative advantage over time. Moreover, this observa-
tion demonstrates that the dropout gap is not limited to junior
researchers but persists at similar rates throughout scientific
careers.
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AB
CD
EF
Fig. 4. Author’s age-dependent dropout rate. (A) Dropout rate for male (blue) and female (orange) authors over their academic ages. (B) The cumulative
survival rate for male and female authors over their academic ages. (C and D) The effect of controlling for the age-dependent dropout rate on the gender
gaps in total productivity (C) and impact (D). (E) The total impact gap is eliminated in the matched sample based on total productivity. (F) The gender gap
in the total number of collaborators is eliminated in the matched sample based on total productivity.
The average causal effect of this differential attrition is
demonstrated through a counterfactual experiment in which we
shorten the careers of male authors to simulate dropout rates
matching their female counterparts at the same career stage
(Fig. 4 C and D and SI Appendix, section S4.F). We find that
under similar dropout rates, the differences in total productiv-
ity and total impact reduce by roughly two-thirds, namely from
27.4 to 9.0% and from 30.5 to 12.1%, respectively. This result,
combined with our previous matching experiment (Fig. 3 D and
E), suggests that the difference in dropout rates is a key fac-
tor in the observed total productivity and impact differences,
accounting for about 67% of the productivity and impact gaps.
Yet, the differential dropout rates do not account for the whole
effect, suggesting that auxiliary disruptive effects, from percep-
tion of talent to resource allocation (15, 21), may also play a
potential role.
The reduction of the gender gaps in both total productiv-
ity and total impact by similar amounts suggests that total
impact, being the summation over individual articles, may be
primarily dependent on productivity (15). To test this hypoth-
esis, we conducted another matching experiment in which we
selected a male author from the same discipline and with exactly
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SOCIAL SCIENCES
the same number of total publications as each female author
(SI Appendix, section S4.D). In these matched samples, the
gender gap in the total impact is completely eliminated, drop-
ping from 38.4% in favor of male authors to 0.8% in favor
of female authors (Fig. 4E). This reveals a second gender-
invariant quantity—there is no discernible difference in impact
between male and female scientists for the same size body
of work. This second gender invariant reinforces our main
finding that it is career-length differences that drive the total
productivity gap, which consequently drives the impact gen-
der gap in academia. Interestingly, controlling for productivity
similarly flips the gender gap in the total number of collabora-
tors throughout a career, from 13.3% in favor of male authors
to 16% in favor of female authors (Fig. 4F and SI Appendix,
section S4.E).
Summary and Discussion
The reconstruction of full publishing careers of scientists allowed
us to confirm the differences in total productivity and impact
between female and male scientists across disciplines and coun-
tries since 1955. We showed that the gradual increase in the
fraction of women in STEM was accompanied by an increase in
the gender disparities in productivity and impact. It is particularly
troubling that the gender gap is the most pronounced among the
highly productive authors—those who train the new generations
of scientists and serve as role models for them. Yet, we also
found two gender invariants, revealing that active female and
male scientists have largely indistinguishable yearly performance
and receive a comparable number of citations for the same size
body of work. These gender-invariant quantities allowed us to
show that a large portion of the observed gender gaps are rooted
in gender-specific dropout rates and the subsequent gender gaps
in publishing career length and total productivity. This finding
suggests that we must rephrase the conversation about gen-
der inequality around the sustainability of woman’s careers in
academia, with important administrative and policy implications
(16, 37, 48–53).
It is often argued that in order to reduce the gender gap, the
scientific community must make efforts to nurture junior female
researchers. We find, however, that the academic system is losing
women at a higher rate at every stage of their careers, suggesting
that focusing on junior scientists alone may not be sufficient to
reduce the observed career-wise gender imbalance. The cumula-
tive impact of this career-wide effect dramatically increases the
gender disparity for senior mentors in academia, perpetuating
the cycle of lower retention and advancement of female faculty
(10, 53–55).
Our focus on closed careers limited our study to careers that
ended by 2010, eliminating currently active careers. Therefore,
further work is needed to detect the impact of recent efforts
by many institutions and funding agencies to support the par-
ticipation of women and minorities (41, 56). Our analysis of
all careers and the factors that dominate the gender gap could
offer a baseline for such experimental studies in the future.
Due to the reliability of gender disambiguation, we were also
unable to assess author gender for China, Japan, Korea, Brazil,
Malaysia, and Singapore, whose inclusion would provide a more
comprehensive global perspective of gender differences in sci-
ence. Since scientists from these countries significantly increased
their contributions to the global scientific discourse, there is a
pressing need for future work to develop more accurate gen-
der identification methodologies. Despite these limitations, our
work suggests the importance of temporal controls for study-
ing academic careers and, in particular, gender inequality in
academia.
It is important to emphasize that the end of a publishing
career does not always imply an end of an academic career;
authors who stopped publishing often retain teaching or admin-
istrative duties or conduct productive research in industry or
governmental positions, with less pressure to communicate their
findings through research publications. Scientific publications
represent only one of the possible academic outputs; in some
academic disciplines, books and patents are equally important,
and all three of our data sources (WoS, MAG, and DBLP)
tend to overrepresent STEM and English language publications
(57), thereby possibly biasing our analysis. Furthermore, our
bibliometric approach can draw deep insight into the large-scale
statistical patterns reflecting gender differences, and yet we can-
not observe and test potential variation in the organizational
context and resources available to individual researchers (13,
58). However, our results do suggest important consequences
for the organizational structures within academic departments.
Namely, we find that a key component of the gender gaps
in productivity and impact may not be rooted in gender-
specific processes through which academics conduct research
and contribute publications but by the gender-specific sustain-
ability of that effort over the course of an entire academic
career.
Data and Code Availability. The DBLP and MAG are publicly
available from their source websites (SI Appendix). Other related
and relevant data and code are available from the corresponding
author upon request.
ACKNOWLEDGMENTS. We thank Alice Grishchenko for help with the visu-
alizations. We also thank the wonderful research community at the Center
for Complex Network Research, and in particular Yasamin Khorramzadeh,
for helpful discussions, and Kathrin Zippel at Northeastern University for
valuable suggestions. A.J.G. and A.-L.B. were supported in part by Temple-
ton Foundation Contract 61066 and Air Force Office of Scientific Research
Award FA9550-19-1-0354. J.H. and A.-L.B. were supported in part by
Defense Advanced Research Projects Agency Contract DARPA-BAA-15-39.
R.S. acknowledges support from Air Force Office of Scientific Research
Grants FA9550-15-1-0077 and FA9550-15-1-0364.
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Discussion

An important finding from this paper, "This suggests the productivity and impact of gender differences are explained by different publishing career lengths and dropout rates." Always be careful when evaluating proportions without controlling for disciplinary differences! Just take it from Simpson... https://en.wikipedia.org/wiki/Simpson%27s_paradox Albert-Laszlo Barabasi is a physicist and network scientist who introduced the concept of scale-free networks and proposed the Barabási–Albert model to explain their widespread emergence in natural, technological and social systems. He is the director of the Center for Network Science at Northeastern University. Here is a link to the "Emergence of Scaling in Random Networks": https://science.sciencemag.org/content/286/5439/509.full Source: https://en.wikipedia.org/wiki/Albert-L%C3%A1szl%C3%B3_Barab%C3%A1si This access to the full publishing career data was key to their discovery of the different career lengths of male and female researchers.