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RESEARCH | REVIEW

(25–27). Papers of this type are twice as likely to according to their citation scores, which may previous output, markedly boosts the num-
receive high citations (26). In other words, a be rooted in a selection bias that offers better ber of citations collected by that paper in the
balanced mixture of new and established ele- career opportunities to better scientists (43, 44). first years after publication (47). After this
ments is the safest path toward successful re- Moreover, scientists tend to move between in- initial phase, however, impact depends on the
ception of scientific advances. stitutions of similar prestige (45). Nevertheless, reception of the work by the scientific com-
when examining changes in impact associated munity. This finding, along with the work re-
Career dynamics with each move as quantified by citations, no ported in (46), suggests that, for productive
Individual academic careers unfold in the con- systematic increase or decrease was found, not scientific careers, reputation is less of a critical
text of a vast market for knowledge production even when scientists moved to an institution of driver for success than talent, hard work, and
and consumption (28). Consequently, scientific considerably higher or lower rank (46). In other relevance.
careers have been examined not only in terms words, it is not the institution that creates the A policy-relevant question is whether creativity
of individual incentives and marginal productivity impact; it is the individual researchers that make and innovation depend on age or career stage.
(i.e., relative gain versus effort) (29), but also an institution. Decades of research on outstanding researchers
institutional incentives (30, 31)and competition Another potentially important career factor and innovators concluded that major break-
(32). This requires combining large repositories is reputation—and the dilemma that it poses throughs take place relatively early in a career,
of high-resolution individual, geographic, and for manuscript review, proposal evaluation, and with a median age of 35 (48). In contrast, recent
temporal metadata (33) to construct represen- promotion decisions. The reputation of paper work shows that this well-documented propen-
tations of career trajectories that can be ana- authors, measured by the total citations of their sity of early-career discoveries is fully explained
lyzed from different perspectives. For example, by productivity, which is high in the early stages
one study finds that funding schemes that are of a scientist’s career and drops later (49). In
tolerant of early failure, which reward long-term other words, there are no age patterns in in-
success, are more likely to generate high-impact novation: A scholar’smostcited papercan be any
publications than grants subject to short review of his or her papers, independently of the age or
cycles (31). Interacting systems with competing career stage when it is published (Fig. 3). A
time scales are a classic problem in complex sys- stochastic model of impact evolution also indi- Downloaded from
tems science. The multifaceted nature of science cates that breakthroughs result from a combina-
is motivation for generative models that high- tion of the ability of a scientist and the luck of
light unintended consequences of policies. For picking a problem with high potential (49).
example, models of career growth show that non-
tenure (short-term) contracts are responsible Team science
for productivity fluctuations, which often result During past decades, reliance on teamwork has
in a sudden career death (29). increased, representing a fundamental shift in
Gender inequality in science remains preva- the way that science is done. A study of the
lent and problematic (34). Women have fewer authorship of 19.9 million research articles and http://science.sciencemag.org/
publications (35–37) and collaborators (38)and 2.1 million patents reveals a nearly universal
less funding (39), andtheyare penalizedinhiring shift toward teams in all branches of science
decisions when compared with equally qualified (50) (Fig. 4). For example, in 1955, science and
men (40). The causes of these gaps are still un- engineering teams authored about the same
clear. Intrinsic differences in productivity rates number of papers as single authors. Yet by 2013,
and career length can explain the differences the fraction of team-authored papers increased
in collaboration patterns (38) and hiring rates to 90% (51).
(35) between male and female scientists. On the Nowadays, a team-authored paper in science on March 1, 2018
other hand, experimental evidence shows that and engineering is 6.3 times more likely to re-
biases against women occur at very early career ceive 1000 citations or more than a solo-authored
stages. When gender was randomly assigned paper, a difference that cannot be explained by
among the curricula vitae of a pool of applicants, self-citations (50, 52). Onepossiblereasonisa
the hiring committee systematically penalized team's ability to come up with more novel com-
female candidates (40). Most studies so far have binations of ideas (26) or to produce resources
focused on relatively small samples. Improvements that are later used by others (e.g., genomics).
in compiling large-scale data sets on scientific Measurements show that teams are 38% more
careers, which leverage information from differ- likely than solo authors to insert novel combina-
ent sources (e.g., publication records, grant ap- Fig. 3. Impact in scientific careers. (A) Publica- tions into familiar knowledge domains, support-
plications, and awards), will help us gain deeper tion record of three Nobel laureates in physics. ing the premise that teams can bring together
insight into the causes of inequality and motivate The horizontal axis indicates the number of years different specialties, effectively combining knowl-
models that can inform policy solutions. after a laureate’s first publication, each circle edge to prompt scientific breakthroughs. Having
Scientists’ mobility is another important factor corresponds to a research paper, and the height more collaborations means greater visibility
offering diverse career opportunities. Most mo- of thecirclerepresentsthe paper’simpact, through a larger number of coauthors, who will
bility studies have focused on quantifying the quantified by c 10 , the number of citations likely introduce the work to their networks, an
brain drain and gain of a country or a region after 10 years.The highest-impact paper of a enhanced impact that may partially compensate
(41, 42), especially after policy changes. Research laureate is denoted with an orange circle. for the fact that credit within a team must be
on individual mobility and its career effect re- (B) Histogram of the occurrence of the highest- shared with many colleagues (29).
mains scant, however, primarily owing to the impact paper in a scientist’ssequenceof Work from large teams garners, on average,
difficulty of obtaining longitudinal information publications, calculated for 10,000 scientists.The more citations across a wide variety of domains.
about the movements of many scientists and flatness of the histogram indicates that the Research suggests that small teams tend to dis-
accounts of the reasons underlying mobility de- highest-impact work can be, with the same rupt science and technology with new ideas and
cisions. Scientists who left their country of origin probability, anywhere in the sequence of papers opportunities, whereas large teams develop ex-
outperformed scientists who did not relocate, published by a scientist (49). isting ones (53). Thus, it may be important to

Fortunato et al., Science 359, eaao0185 (2018) 2 March 2018 3of 7