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the handiness of powerful computational instruments and recent improvements in multidisciplinary methods are providing researchers an ever - greater opportunity to investigate societies in their complex nature @xcite .
several research outcomes have been showing that men and women differ in characteristics that could be related to their collaboration patterns .
research collaboration is increasing in frequency and scope .
it is driven , among other causes , by growing relationship across scientific disciplines , improvement of the efficiency in research resources in projects and development of information and communication technologies @xcite .
the motivations @xcite , strategies , patterns and impacts on scientific productivity in quantity and quality in research collaboration have received great scholarly attention ( @xcite;@xcite;ductor15 ) .
the patterns vary across space ( @xcite;@xcite ) , academic ranks @xcite , professional origins @xcite and scientific disciplines @xcite .
economic science makes connections with many other scientific disciplines , like statistics or social sciences , like sociology , history or management ( @xcite;@xcite ) .
economics shows a growing increase of co - authorship ( @xcite;@xcite;@xcite ) . on average ,
a researcher in economics had less than one co - author in the 1970s , 1.24 co - authors in the 1980s and 1.67 in 1990s ( @xcite;@xcite ) .
gender differences in collaborative research concerning motivations , strategies , patterns and impacts on science performance have received little attention , contrasting with the growing importance that women hold in academia and research .
the literature shows mixed results about the gender differences concerning research collaboration strategies @xcite , impacts ( @xcite;@xcite;@xcite-@xcite ) and patterns ( @xcite-@xcite ) .
bibliometric studies and survey analysis are the main methodologies to the study of research collaboration @xcite .
large bibliometric databases like web of science ( @xcite;@xcite;@xcite ) are the main sources used to bibliometric analysis . however , that bibliometric databases have a strong weakness concerning the study of the differences by gender ; they do not include information separated by male - female and the way to overcame that weakness is to obtain the information from the first name nal04 or the family name of the author @xcite .
the present paper seeks to build upon the previous analysis about gender aspects in research collaboration which literature was recently surveyed in @xcite . here
, we intend to contribute to at least two points of the literature : the differences of research collaboration and interdisciplinary participation by gender .
focusing in economics , a scientific subject strongly connected to other scientific domains @xcite and constructing five categories of articles in a gender authorship perspective , this study addresses both issues : research collaboration and interdisciplinarity .    applying a network approach and using as unit of analysis articles indexed in the web of science ( wos ) this analysis maps the research collaboration by gender within dozen of scientific subjects , all associated with economics .
the choice of network approaches to study research collaboration in economics @xcite has been extensively embraced .
it often relies on the discovery of patterns of collaborations within researcher communities , aiming to find the influence of individual researchers in the networks using citation analysis .
reference beaver78 , in the first complete theory of scientific collaboration , list and discuss the causes for that collaboration .
they stress that it is necessary , when scientists deal with research questions , that cross disciplinary bounds .
they also identify a large variation in collaboration by discipline , which is being further investigated in more recently published studies ( @xcite;@xcite ) .
its well known that the adoption of a network approach allows the modeling of social structures from a bottom - up perspective , as resulting from the interaction ( or likeness ) of individual characteristics @xcite .
moreover , as the individual characterization might be driven by multiple aggregate concerns , the network approaches allow for simultaneously considering that multiplicity of individual aspects and the consequences of the aggregate structures themselves on the emergence of collective patterns .
meanwhile , in the adoption of a network approach , one shall be aware that the choice of a given network representation is only one out of several other ways to look at a given set of elements .
as connecting the elementary units of a system may be conceived in many different ways , that choice may depend strongly on the available empirical data and on the questions that a network analysis aims to address @xcite .
the main question addressed in this paper is whether some relevant characteristics of research collaboration would emerge in networks where subjects are linked whenever they co - occur in a common paper .
we hypothesized that gender imbalance in authorship of papers might influence the shape of those networks , allowing to uncover patterns from gender differences .
if it happens , the emerging patterns may help to understand important characteristics of research collaboration , of the relationship among subjects and its relation to gender .
the paper is organized as follows : next section presents the empirical data we work with and some preliminary statistical results .
section 3 describes the network approach and the results from its application .
section 4 concludes .
the web of science ( wos ) is one of the major bibliometric databases ( together with google scholar and scopus ) and includes all scientific subjects .
it comprises a total of 11,990 journals ( 8,778 from science and 3,212 from social sciences ) @xcite .
concerning the scientific domain of economics , it includes 334 publications .
the wos classifies each journal in one or more subjects ( or categories ) .
taking as examples the journals * journal of informetrics * and * research policy * , the former is classified in `` computer science , interdisciplinary applications '' and `` information science & library science '' , while the latter is classified in `` management '' and `` planning & development '' .    from the original wos database a selection of articles was carried on adopting as criteria : articles published in wos indexed journals over the period 2010 - 2015 , having economics as scientific subject and at least one author affiliated to a portuguese institution .    our motivation to focus on the field of economics and on the papers whose
authors are affiliated to portuguese institutions is twofold :    1 .
economic science makes connections with many other scientific subjects .
2 .   according oecd data , portugal presents the highest percentage of women in research during the period of 2004 - 2012 ( oecd , 2016 ) .
consequently , our approach is applied to a data set comprising 1,138 papers published in 2010 , 2011 , 2012 , 2013 , 2014 and 2015 and having economics as the main subject matter .    besides economics
, each paper may have extra ( or secondary ) subjects .
table 1 presents the set of secondary ( extra ) subjects found in our data set .
each paper in the data set is coded by a string that informs about the presence of extra subjects . in the broader set of 1,138 papers having economics as the main subject matter , 29 different extra ( or secondary ) subjects were found .    [ cols="<,<",options="header " , ]     table 4 : topological coefficients computed from the mst of each authorship category .
although the five networks have similar sizes , there is a remarkable difference in the values obtained for the man exclusive tree ( m.exc-mst ) .
when women are excluded , the network of subjects displays an much higher diameter ( @xmath0 ) , showing large distances among subjects are enlarged .
the also important decrease in the number of leafs ( @xmath1 ) indicates that this network develops a entirely different structure when compared with the other msts by authorship category .
the plots in figure 10 show the number of leafs ( @xmath2 , the diameter ( @xmath3 and the ratio @xmath4 across the different categories of authorship . as ,
depending on the specific tree motif , the values of @xmath0 and @xmath5 move in opposite directions , in computing the absolute value of the difference @xmath6 relative to @xmath7 helps to emphasize the distinguish structure of the mst that characterizes the man exclusive network ( m.exc-mst ) .    in the broader set of papers published in wos indexed journals over the period 2010 - 2015 in the scientific domain of economics and having at least one author affiliated to a portuguese institution , as the percentage of female authorship decreases , the mst obtained from the corresponding network of subjects moves from a star configuration to a path motif . in so doing ,
the larger distances between subjects are enlarged and the number of poorly connected subjects increases . if , conversely , the network of subjects has a high percentage of female authorship , the corresponding mst approaches a star motif , the number of leafs is enlarged and the corresponding diameter decreases .
there are many ways to link the elementary units of system in order to induce a network .
choosing the most suitable way depends strongly on the available empirical data and on the research questions that a network analysis aims to address .
regarding available empirical data , most of bibliometric databases have a strong weakness concerning the study of the differences by gender .
in what concerns research questions , gender differences in collaborative research and interdisciplinarity in scientific outputs have received little attention when compared with the growing importance that women hold in academia and research .    from the set of papers published in wos indexed journals over the period 2010 - 2015 in the scientific domain of economics and having at least one author affiliated to a portuguese institution
, our results apparently converge to the hypothesis that women prefer to work in teams .
however , they also indicate that when papers are exclusively authored by women , the working teams tend to be smaller than any of those that also include men .
these results converge to the mixed results reported in the literature , where different units of analysis , measures , methods and samples were adopted ( @xcite;@xcite ; @xcite-@xcite ) .
regarding interdisciplinarity , our findings seem to contradict the hypothesis that women have more propensity to interdisciplinary research collaboration @xcite .
moreover , we found that academic women in economics compared with their male counterparts reveal preference for the subjects environmental sciences , management and political sciences and that , conversely , the subjects social sciences , mathematics and finance display higher frequencies in papers either inclusively or exclusively authored by men .
our main contribution relies in the adoption of a network approach allowing to uncover the emergence of a specific pattern when the network of scientific subjects is induced from a set of papers exclusively authored by men .
such a male exclusive authorship condition is found to be the solely responsible for the emergence of that specific shape in the structure of the network .
moving away from a _ star _ motif together with the loss of centrality of the subject management have an important bearing on the structure of the  male exclusive authorship network : when papers authorship includes just men , the larger distances between subjects in the network become even larger and this is mainly due to a decrease in the relative number of papers having management as a secondary subject .
we find enough evidence that gender imbalance in scientific authorships brings a peculiar trait to the networks of subjects .
such a peculiar trait might facilitate future network analyses of research collaboration and interdisciplinarity .
acknowledgement : financial support by fct ( fundao para a cincia e a tecnologia ) , portugal is gratefully acknowledged .
this article is part of the strategic project : uid / eco/00436/2013 .
the authors thank marilei kroetz for her work in the gender identification process .
frandsen , t. f. ; jacobsen , r. h. ; wallin , j. a. ; brixen , k. ; ousager , j. gender differences in scientific performance : a bibliometric matching analysis of danish health sciences graduates . journal of informetrics 2015 , 9 , 1007 - 1017 .
naldi , f. ; luzi , d. ; valente , a. ; parenti , i. v. scientific and technological performance by gender .
handbook of quantitative science and technology research : the use of publication and patent statistics in studies of s&t systems 2004 , 299 - 314 .
gender differences in collaborative research have received little attention when compared with the growing importance that women hold in academia and research . unsurprisingly , 
 most of bibliometric databases have a strong lack of directly available information by gender . 
 although empirical - based network approaches are often used in the study of research collaboration , the studies about the influence of gender dissimilarities on the resulting topological outcomes are still scarce . here 
 , networks of scientific subjects are used to characterize patterns that might be associated to five categories of authorships which were built based on gender . 
 we find enough evidence that gender imbalance in scientific authorships brings a peculiar trait to the networks induced from papers published in web of science ( wos ) indexed journals of economics over the period 2010 - 2015 and having at least one author affiliated to a portuguese institution . 
 our results show the emergence of a specific pattern when the network of co - occurring subjects is induced from a set of papers exclusively authored by men . such a male - exclusive authorship condition is found to be the solely responsible for the emergence that particular shape in the network structure . 
 this peculiar trait might facilitate future network analyses of research collaboration and interdisciplinarity .    
 keywords : co - occurrence networks , gender , research collaboration , interdisciplinarity , bibliometrics , minimum spanning tree