A LONGITUDINAL ANALYSIS ON INTELLECTUAL STRUCTURE OF HUMAN RESOURCES MANAGEMENT: THEORETICAL FOUNDATIONS AND RESEARCH TRENDS

Öz In this study, the intellectual structure of the field of human resources management (HRM) has been investigated and new theoretical foundations and research trends that will contribute to the development of the field have been proposed. Qualitative content analysis was used in the research and a longitudinal analysis was performed. The results show that sociology-based organizational theories further affected the field in the 1990s. In the 2000s, it was determined that the dominant theories in the field were human capital theory from economy discipline, social exchange theory from sociology discipline, and resource based view from strategic management discipline. In the 2010s, human capital theory from economy discipline, social capital theory from sociology discipline, and resource based view from strategic management discipline had widespread effects in the field. Finally, strategic human resource management (SHRM), outcomes and human resources practices were determined as the research trends that have been most effective on the field from the 1990s to the present. However, the context research trend was less effective in the field compared to other research trends. As a result, it can be stated that future researches that want to contribute to the field of human resources management can benefit from theory of the growth of the firm, Austrian school of economics, strategy as a practice and new institutional economies. In addition, research trends in the future of the field could be stated as the effects of industry 4.0, e-HRM, and artificial intelligence studies on human resource management. Bu çalıĢmada insan kaynakları yönetimi alanının entelektüel yapısı araĢtırılarak, alanın geliĢimine katkı sağlayacak yeni teorik temeller ve araĢtırma eğilimleri önerilmiĢtir. AraĢtırmada nitel içerik analizinden faydalanılmıĢ ve boylamsal bir analiz gerçekleĢtirilmiĢtir. Bulgular, 1990‟lı yıllarda sosyoloji temelli örgüt teorilerinin alanı daha fazla etkilediğini göstermektedir. 2000‟li yıllarda alandaki hâkim teoriler ekonomi disiplininden insan sermayesi teorisi, sosyoloji disiplininden sosyal değiĢim teorisi ve stratejik yönetim disiplininden kaynaklara dayalı yaklaĢım olarak tespit edilmiĢtir. 2010‟lu yıllarda ise ekonomi disiplininden insan sermayesi teorisi, sosyoloji disiplininden sosyal sermaye teorisi ve stratejik yönetim disiplininden kaynaklara dayalı yaklaĢımın alanda yaygın etkileri olduğu bulunmuĢtur. Son olarak stratejik insan kaynakları yönetimi, çıktılar (outcomes) ve insan kaynakları uygulamaları 1990‟lı yıllardan günümüze alana en fazla hakim olan araĢtırma trendleri olarak tespit edilmiĢtir. Ancak bağlama (context) yönelik araĢtırmaların ise diğer araĢtırma trendlerine göre alandaki etkisinin sınırlı olduğu bulgusuna ulaĢılmıĢtır. Sonuç olarak insan kaynakları yönetimi alanına katkı sağlamak isteyen gelecekteki araĢtırmaların firmanın büyüme teorisi, Avusturyan ekonomi okulu, uygulama olarak strateji çalıĢmaları ve yeni kurumsal ekonomilerden yararlanabileceği ifade edilebilir. Ayrıca alanın gelecekte yönelebileceği araĢtırma eğilimlerinin endüstri 4.0, E-ĠKY ve yapay zeka çalıĢmalarının insan kaynakları yönetimi üzerindeki etkileri olacağı belirtilebilir.


INTRODUCTION
As a scientific study field, personnel management or HRM started to develop in the USA during the World War I years (Dulebohn et al., 1995: 21). It is possible to emphasize the importance of certain dates in the development and change history of the field. The field of HRM was commemorated by Taylor's (1914) study of movement and time, which was accepted as the foundation of management science until the 1920s. The basic logic of these studies was dominated by a mechanical understanding aiming to maximize the productivity of employees (Thite et al., 2009: 8). The mechanical understanding on the basis of studies was significantly affected by the lack of labor caused by World War I. Along with the end of the war, the period from the early 1920s to the 1930s was a period in which informal social networks and human relations were examined within the formal organizational structures (Dulebohn et al., 1995). This period was marked by the Hawthorne studies (Mayo et al., 1949). After this period, the field was associated with industrial relations in the period from the 1930s to the 1950s during which Great Depression happened (Ferris et al., 2004: 234-235). This period led to the shift of attention from personnel management to industrial relations. This process directed researchers from many different disciplines such as economics, sociology and anthropology to the field, which played an important role in the development of the field (Kaufman, 1993: 14). In the period from the end of the World War II until the 1970s, the field was highlighted by unionization activities and legal regulations regarding the conditions of employees (Dulebohn et al. 1995). In this period, social issues such as prohibition of discrimination with the effect of trade unions, occupational health and safety, pension rights, tax regulations related to employees and employment relations were on the agenda of the field (Thite et al., 2009: 10). In the period from the 1970s to the 1980s, the focus of the field was evolved from industrial relations to HRM along as unionization movements in the USA lost their influence (Ferris et al., 2004: 234). This change introduced the concepts such as cost, productivity, strategy and competitive advantage to the field (Huselid, 1995: 636). Along with these concepts, employees began to be considered as a source of competitive advantage. This situation revealed SHRM (Strategic Human Resource Management) as a dominant field of study in the field (Wright and McMahan, 1992: 295;Schuler et al., 1993: 419;Boxall et al., 2000: 183).
These developments in the field brought along the academic studies examining the evolutionary patterns of the field from different aspects. In this context, Thite et al. (2009: 8) focused on five periods in the evolution of the field in the USA. These periods can be listed as Pre-World War II, Post-World War II (1945-1960), Social Issues Era (1963-1980, Cost-Effective Era (1980 to the early 1990s), Technological Advancement Era and the Emergence of SHRM (1990 to Present). This study provided information about the historical development pattern of the field. However the study Thite et al. (2009) was limited to investigating the effects of technological advances on the field after the 1990s. Mahoney and Deckop (1986: 223), who investigated the evolution of concepts and patterns in the field, discussed a number of issues from personnel administration to HRM, from human resources planning to strategy and from business relations to governance. In another study, Ferris et al. (2004: 233-234) evaluated the historical development of the field as personnel management, HRM and SHRM. Although both studies provided information about the development of the field, they did not make a longitudinal evaluation of the intellectual structure of the field. Fernandez-Alles and Ramos-Rodríguez (2009: 161), who examined the intellectual foundations of the field with bibliometric analyses they carried out between the years 1985 and 2005, gave more detailed explanations to the intellectual structure of the field compared to the studies listed here. The authors provided detailed information based on an objective method regarding the researchers who constituted the basis of the field and the issues in the field. However, the study was limited to the review of predominant authors in the field and the Journal of Human Resources Management. Finally, Lengnick-Hall et al. (2009: 65), who examined the evolution of SHRM historically and chronologically, focused on seven issues that played a role in the evolution of the field. Authors listed these issues as 1explanining contingency perspectives and fit, 2-shifting from a focus on managing people to creating strategic contributions, 3-elaborating HR system components and structure, 4-expanding scope of SHRM, 5achieving HR implementation and execution, 6-measuring outcomes of SHRM and 7-evaluating of methodological issues. This study subjectively structured the literature it reviewed and did not present objective explanations. This study differs from the studies evaluated above in that it longitudinally examined the disciplinary, theoretical and research trends-based evolution of the field of human resources between 1990-2018. Thus, it was aimed to provide empirical contributions to the studies on the theoretical foundations of the field of study Jackson and Schuler, 1995;Delery and Doty, 1996;Ferris et al., 2004;Ferris et al., 1999) and its intellectual structure (Fernandez-Alles and Ramos-Rodríguez, 2009). The second contribution of the study is that it enables to examine the evolution of the theoretical foundations and subject orientation of the field in time. Finally, the study makes contributes to the development of the field by proposing new theories and research trends that have the potential to examine facts and variables in the field of human resource management.
In this context, the study sought answers to three questions: "1-What kind of changes took place in the effects of theories contributing to the field of HRM from the 1990s to the present on the field? 2-What kind of changes have research trends in the field undergone from the 1990s to the present?" As a result of the findings to be obtained within the framework of these two research questions, our study aimed to determine the theories and research trends used in the field of HRM. Thus, the theories and research trends that were not used but have the potential to be used in the field of HRM could be determined. In this context, the third question that our research sought to answer was 3-From which theories and research trends can the field of HRM benefit in the future? Based on these questions, the study consisted of four sections. The studies on the theoretical foundations of the field of human resources and the criticism of these studies are presented in the first section. The second section provides information about the method of research and the process of obtaining data. The third section includes the findings of the study and the evaluations of the findings. Finally, the study was completed with the discussion and conclusion section.

LITERATURE REVIEW
Academic studies in the field of HRM emerged by the intersection of the concepts and theories in economics, sociology, psychology and management sciences. This interdisciplinary development, which creates a fragmented appearance in the field (Ferris et al., 2004: 231), increased the criticism on the field that there is no coherent theoretical foundation (Wright and McMahan, 1992: 295;Delery and Doty, 1996: 802) and no research trend. Criticisms directed different scientists to examine the theoretical foundations and research trends of the field.
The first review of theoretical foundations was performed by Wright and McMahan (1992: 300). Authors mentioned the presence of seven theories in the theoretical foundations of the field of SHRM. They listed these theories as the resource based view, contingency theory, open system theory (general system theory), agency theory, transaction cost theory, resource dependency/power theory and institutional theory. Although this study enabled to examine different variables related to the field of SHRM, it did not provide a comprehensive explanation of the theoretical foundations. Furthermore, the study was based on subjective literature reviews and was not supported by any empirical finding.
A similar study on theoretical foundations was carried out by Jackson and Schuler (1995: 238-239). Authors proposed eight theories to understand HRM practices in the context of organizations and their surroundings. They listed these theories as the general system theory, role behavior perspective, institutional theory, resource dependency theory, human capital theory, transaction cost theory, agency theory and resource based view. This study also has the limitations mentioned in the previous study. Moreover, it also does not provide detailed information on which theories were used in the theoretical foundations of HRM within a certain time period.
Other scientists discussing the criticisms for the absence of a coherent theoretical foundation are Delery and Doty (1996), Martin-Alcazar et al. (2005) and Guest (1997). From among the researchers, Delery and Dotty (1996: 805)  best HRM practices, the contingency approach is the theorization method emphasizing the conditions specific to HRM, and the configurational approach is the theorization method emphasizing the internal and external coherence of the firm. Martin Alcazar et al. (2005: 637-639) contributed to these theorization methods by adding contextual perspective. Contextual perspective is an approach that makes explanations about industrial context, institutional context and international context. In another study, Guest (1997: 264-265) classified the theories in the field as strategic, descriptive and normative theories. Strategic theories investigate the relationships between external conditions and HRM policies and practices. Descriptive theories provide a classification of the content of HRM practices and the consequences of these practices. Normative theories reflect the view that there is a sufficient source of information to provide a basis for the best practices, or that a set of values indicates the best practice. All of the studies reviewed here were limited to the investigation of theorization methods in the field of HRM and did not provide a detailed explanation of the theoretical foundations of the field. Fisher (1989: 160), who was a scientist evaluating research trends in the field of HRM, mentioned the presence of research trends such as international human resource management (IHRM), mergers and acquisitions and downsizing, in addition to SHRM, in the field. Furthermore, the author also focused on operational-level research subjects such as selection, training, compensation and performance appraisal. While Ferris and Judge (1991: 449), from among other researchers who examined the issue, focused on Political Perspective on Human Resources Management, Ferris et al. (1999: 386) discussed SHRM, IHRM and Political Perspectives. Besides these trends, Ferris et al. (1999: 400) considered the issues such as accountability, diversity, justice, symbolic and reputational considerations as the new trends that could contribute to the field. Boxall et al. (2007: 2), who finally addressed the issue, argued that the field of HRM was dominated by three sub-research areas: micro HRM, SHRM and IHRM. None of the studies evaluating research trends in the field of HRM could fully reflect the whole picture since they were not based on empirical and longitudinal findings.
The studies related to the development of the field of HRM were also discussed in Turkish literature (Akar, 2013;Arı and Boylu, 2015;Benligiray, 2009;Erçek, 2004;Kızıldağ and Böyükaslan, 2018;Sayılar, 2005;Üsdiken and Wasti, 2002). In those studies, Üsdiken and Wasti (2002) discussed the ways how studies carried out in Turkey established links with the United States-based literature. The authors concluded that the links established with foreign literature, and the concepts and theories in this literature were tested within the context of Turkey. Sayılar (2004) discussed the strategic perspectives developed in the field of HRM under the leadership of the United States since the 1980s and examined the theoretical developments, research questions and solutions that developed within the framework of SHRM. The author mentioned the issues that could be brought along by the main flows developing in the context of the United States on the way to explain the context of Turkey. Apart from these two studies, other studies in Turkish literature focused on the literature and discourses in the context of Turkey in the field of HRM. Unlike those studies, our study revealed the theoretical foundations and the developments in research trends in the United States-based literature by examining the journals in the context of these countries. The adoption of the United States as the only reference and source of learning after the 1960s was effective in the preference for this literature (Üsdiken and Wasti, 2002). Therefore, our study is not associated with HRM literature in different countries and in the context of Turkey, which can be considered as a limitation of our study. The next section involves the method to reveal this longitudinal finding.

METHOD
The content analysis aswas used in this study. The most influential articles in the field of HRM were determined through Social Science Citation Index (SSCI) of Web of Science (Acedo et al., 2006: 630;Ramos-Rodríguez and Ruíz-Navarro, 2004: 983). These articles were also analyzed in depth through content analysis, and theories and research subjects in the basis of the field were determined. In the study, which journals would be used was first determined. Google academic metrics were used to determine the journals. Google metrics was preferred because it enables the determination of the most influential journals in the field of human resources. Business, economics and management were first selected from the categories in metrics, and then human resources and organizations were selected from sub-categories. Through these selections, top five journals with the best h5 index 1 and h5 median value 2 (with maximum citation) in the field were determined. The journals used in the study, the article numbers obtained from journals, and the impact scores of these journals are presented in Table 1. In the study, the use of only the journals given in Table 1 caused that the journals and books within the context of different countries were left out examination, which can be considered an important limitation for our study. After determining the journals, the process of obtaining data from SSCI database was initiated. Since SSCI is the most commonly used database (Zupic and Čater, 2014: 60), this database was considered appropriate to be used in the study. However, the use of only this database posed an obstacle for the examination of the studies in other databases such as Scopus and Google Scholar, which can be expressed as another limitation of our study.
SSCI sorting criteria were used to reveal the data. First, after the "topic" search on web of science home page in the form of "human resource", data in the fields of management and business were filtered. Then, article was selected as the document type. At this stage, the reason for selecting articles is that academic articles are considered as the validated sources of information (Fernandez-Alles and Ramos-Rodríguez, 2009: 163). Then, five journals given in Table 1 were marked from "source title". As a result of this data filtering process, 308 articles in the field of HRM were reached. With this ranking, the most influential studies in the field of HRM were determined, and thanks to these filtering processes and measurements, the literature is structured in an objectively.
All 308 articles were included in the document analysis in order to reveal the evolutionary patterns of the field. All articles were independently coded by four authors to improve reliability and validity in the analyses. In the first stage of the qualitative content analysis, the titles and key words of the articles were first examined. Then, the abstracts and introductions of the articles were read and it was determined whether they were related to human resources. In this process, articles were divided into two: "related to human resources" and "not related to human resources". As a result of the distinction, it was determined that 205 articles were related to human resources and 103 articles were not related to human resources. Then, it was investigated on which theory/theories 205 articles that were determined to be related to human resources were based. At this stage, the studies were coded as "there is theory" and "no theory". As a result of the coding, it was concluded that 153 articles benefited from a theory or theory group and 52 articles did not benefit. Then, it was determined on which theories 153 studies that were coded as there is theory were based. These theories are presented in detail in Table 2. The distinctions of 153 studies according to periods, theories and authors are presented in Appendix A.
In the second stage of content analysis, the issues in the field were presented. The keywords of the articles were used in the first stage to achieve this result. In the articles with no keywords, dependent and independent variables of the studies, titles in the text contents, and the research topics highlighted in the introduction and abstract sections of the articles were used. Then, the research subjects determined were coded by following the stages of subcategories, categories and main categories (Schreier, 2012;Strauss, 1987;Flick, 2018;Bowen, 2009;Miles et al., 1994). All procedures in this process were conducted separately by four researchers (Weber, 1990). In cases where different topic titles and coding were determined among researchers, agreement was ensured among four authors through discussion (Üsdiken and Wasti, 2002: 15). In the next process, the frequency of repetition of the main codes according to periods are presented in Table 3. As a result of these analyses, the changes undergone by the subjects in the field of HRM in the historical process were determined.

FINDINGS
The findings achieved as a result of the analysis were presented within the frame of two research questions guiding the study. Firstly, from which theories it benefits is presented in Table 2. Secondly, what kind of course research subjects followed in the field in time is presented in Table 3. The results obtained from the analyses are presented in three time periods. These periods are the 1990s, 2000s and 2010s. The aim to be achieved through this classification is to be able to see the change of the evolutionary patterns of the field in time within ten (10) year periods (Üsdiken and Wasti, 2002: 18-20). A 10-year period was determined based on the assumption that a field would not change within a short period of several years.

Effects of Theories
Analysis result achieved by the analyses is the changing effect of the contributions of theories to the field of HRM in time. The distribution of theories according to disciplines, their frequency of use in the studies in the field of HRM, and the change in usage rate are presented in Table 2. According to these results, the dominance of sociology-based organizational theories in the field in the 1990s is remarkable. In particular, it is seen that contingency theory (Lawrence et al., 1967;Child, 1972), institutional theory (Meyer and Rowan, 1977;DiMaggio and Powell, 1983) and resource dependency theory (Pfeffer and Salancik, 2003) had widespread effects in the field of HRM. This result indicates that the field is closely related to management sciences in general and to the field of organizational theories in particular. In the 1990s, in addition to these theories, it is remarkable that resource based view from the discipline of strategic management had a high effect on the field of HRM. In this period, it was determined that other theories made relatively equal contributions to the field.
In the 2000s, theories such as human capital from economy (Becker, 1964), social exchange from sociology (Blau, 1964) and resource-based view from strategic management (Barney, 1991) intensely affected the field. In this period, it is seen that micro views of strategic management, such as dynamic capabilities (Teece et al., 1997;Eisenhardt and Martin, 2000) and knowledge-based view (Grant, 1996) that emerged with the expansion of resource-based view, started to affect the field. These results are consistent with the study in which Wright et al. (2001: 711) examined the effects of dynamic capabilities and knowledge based view on the field of HRM.
The results of the 2010s indicated that human capital theory from the discipline of economy and resource-based view from the discipline of strategic management increased their effects in the field. Furthermore, social capital theory (Coleman, 1990), social network theory (Granovetter, 1973;1985;Burt, 1992) and social exchange theory from the discipline of sociology started to affect the field in these years. This indicated that different theories had effects on the field in the discipline of sociology from the 1990s to the 2000s and 2010s. Note: f refers to frequency of use of the theories and p refers to percentage of use of the theories.
Another finding that can be concluded from the evaluation of Table 2 is the use of neoclassical economy theory and behavioral theory of the firm together in the field in 2010. Of these theories, neoclassical economy is based on the assumption of rational actor while behavioral theory of the firm accepts the assumption of boundedly rational actor, which reveals that the competing assumptions exist together in the field.
Finally, it was concluded that no theory dominantly affecteded the field in the discipline of psychology from the 1990s to the 2010s. Furthermore, it is seen that dominant theories in the field were also different in the discipline of psychology from the 1990s to the 2010s. In other words, it is remarkable regulatory focus theory (Higgins, 1998) and social identification theory (Tajfel and Turner, 1979) had effects on the field in the 2000s, and organizational learning theory (Argyris and Schön, 1978), creativity theory (Amabile, 1983; and cognitive theory (Bandura, 1986) had effects on the field in the 2010s. Another finding indicates that the discipline of psychology contributes more to the field of HRM with cognitive theories. Furthermore, the discipline of psychology is considered as the discipline that has provided the maximum diversity of theories in the field from the 1990s to the present compared to other diplines in Table 2. Finally, a general evaluation to be made on Table 2 revealed that the most effective theories in the field of HRM were resource based view and human capital theory, respectively. Along with these evaluations, our first research question in the form of what kind of changes took place in the effects of theories contributing to the field of HRM from the 1990s to the present on the field? was answered.

Effects of Research Trends
The results related to the second research question in the form of what kind of changes have research trends in the field undergone from the 1990s to the present? are presented in Table 3. Within the framework of this research question, four main categories consisting of SHRM, outcomes, context and human resource practices/functions were determined in the field. The stages of sub categories, categories and main categories were followed in the determination of these categories, as mentioned in the method section. In the creation of categories, support was provided from two (2) scientists from the HRM department, in addition to evaluations made by four researchers together. Outcomes 1-HRM practices outcomes: Flexible work hours, flexible plans, functional flexibility, flexible schedule, flexibility oriented HRM system, high involvement work practices 2-Organizational outcomes: Organizational commitment, organizational citizenship, organizational behavior (diversity/gender) organizational cohesiveness, organizational justice, organizational trust, organizational change, organizational learning, employer branding, high involvement management, work family issues 3-Individual outcomes: Job satisfaction, employee attitude, employee perception, employee helping behavior, psychological ownership, social psychological contract, resistance to change, supportive co-workers, job autonomy 4-Performance outcomes: Micro: Individual, job, absenteeism, creativity, employee quit rates/ Macro: Organizational, financial, innovation, team, unit, turnover, retention, turnover intensions, collective turnover, layoff, voluntary turnover 22 27 57 40 85 40 164  Moreover, the study of BağıĢ and Hızıroğlu (2018) was used in determining the concepts in SHRM, the study of Guest (1997) was used in determining the categories in outcomes, the studies of Ferris et al. (1998) and Jackson and Schuler (1995) were used in determining the categories in context, and finally, the studies of Boxall et al. (2007) were used in determining the categories in HRM practices/functions. The results obtained as a result of these processes are presented in Table 3.
Three categories were determined under the SHRM main category. They were at the individual level, organizational level and interorganizational/interpersonel level. Individual decision making, human capital (human resource value, individual differences, personality traits, expertise, cognitive ability, skills, ability), top/senior/executive management team, professional manager (empowering leadership, leadership, experience, belief, transformational leadership) strategic choice, entrepreneurship, bargaining power and administrative information were evaluated under the individual level category. Individual level findings indicated that the studies mainly focused on the skills, abilities and expertise of human resources, and the senior management team focused on its actions such as decision-making, leadership, entrepreneurship and strategic choice. Capabilities/competencies, business strategy, strategic orientation, organizational ambidexterity, exploration, explotation, adaptation, firm growth, strategic implementation, absorptive capacity, strategic flexibility, patents, r&d strategy, sourcing strategy, diversification, knowledge management, knowledge exchange, power, politics, organizational policy and human resources subcategories were discussed under the organizational level category. The findings at this level revealed that the studies mostly focused on strategy and innovation. Social resources, social capital, social networks and relational coordination subcategories were analyzed under the interorganizational/interpersonel level category. Based on the results obtained, it is seen that the effect of the field of SHRM on the field of HRM increased from the 1990s to the 2010s, which causes that the field of HRM is now referred to as the field of SHRM. In other words, the field that started in the form of personnel management and evolved as HRM has evolved into SHRM as strategy-based concepts and theories affected the field.
As a result of the analyses and evaluations performed, under the outcomes main category, four categories were discussed under the titles of HRM practices outcomes, organizational outcomes, individual outcomes and performance outcomes. Outcomes category can be defined as the categories reached as a result of HRM practices and functions. Among these categories, flexible work hours, flexible plans, functional flexibility, flexible schedule, flexibility oriented HRM system and high involvement work practices subcategories were discussed under the HRM practices outcomes. It is remarkable that the emphasises on HRM practices are frequently the concepts emphasizing flexibility. Organizational commitment, organizational citizenship, organizational behavior (diversity/gender), organizational cohesiveness, organizational justice, organizational trust, organizational change, organizational learning, employer branding, high involvement management, and work family issues were examined under the organizational outcomes category. It appears that the findings under the title of organizational outcomes are mostly considered as organizational behaviors, which reveals that the field of HRM has a vague and intertwined boundary with the area of organizational behavior. Job satisfaction, employee attitude, employee perception, employee helping behavior, psychological ownership, social psychological contract, resistance to change, supportive co-workers and job autonomy subcategories were evaluated under the individual level outcomes category since they evoke highlights on individuals.
Under the title of outcomes main category, the title of performance outcomes was lastly determined. The sub-categories determined under this category were divided into micro and macro analysis levels. The subcategories such as individual performance, job performance, absenteeism, creativity and employee quit rates were discussed under the micro-level analysis category. Organizational performance, financial performance, innovation performance, team performance, unit performance, turnover, retention, turnover intensions, collective turnover, layoff and voluntary turnover subcategories were determined under the macro-level analysis category. Based on the results obtained, it is seen that the effects of the studies related to outcomes on the field of HRM have increased from the 1990s to the present. According to other research trends, it can be said that the research trend with the highest effect in the field in the 2000s and 2010s was outcomes.
Another result obtained in our study is that the studies on context in the field of HRM contributed to the field. Three categories were determined under the context main category. They were organizational context, environmental context and international context. On the basis of these categories, organizational group/team, organizational social climate, organizational culture and relational climate were evaluated in the organizational context. Institutional context, institutional change, labor market conditions, strategic factor markets, labor regulation, aging workforce, industry environment, unionization, employment relationship and environmental complexity were discussed in the environmental context. Finally, with respect to this Mehmet Akif Ersoy Üniversitesi İktisadi ve İdari Bilimler Fakültesi Dergisi Yıl: 2019, Cilt: 6, Sayı: 3, ss: 796-814 main category, cultural context, social context, economic context and political context were determined in the international context. It is seen that this research trend had less effect on the field of HRM compared to other trends.
Finally, there is a research trend in the field under the title of HRM Practices/Functions. The titles related to this research trend were evaluated in three categories. These categories were at the individual level, operational level and organizational level. Employee development, empowering and talent management subcategories were discussed under the individual level category. Job design, job analysis, personnel selection, staffing, recruitment (e-recruiting), training, occupational health and safety practices, work flow integration, hiring and work assignment were evaluated under the operational level category. Finally, categories such as organizational design, HRM system design, career, employment contract, outsourcing, high performance work system, reward (pay, compensation cost, and incentives), human resource control system and human resource system were achieved in the organizational level category. This research trend is defined as micro HRM by Boxall et al. (2007: 2) and can be expressed as the research trend that forms the basis of the field of HRM. It can be stated that the effect of this research trend has increased from the 1990s to the present. It can be stated to be the most studied research trend after outcomes in the 2010s.
When an evaluation is made on the results described here by taking into account the previous research results, the results obtained empirically support the results of previous studies. For instance, the results obtained from this study support the study in which Wright et al. (2001: 702) revealed the relationship between the field of SHRM and the resource based view. Similarly, the study carried out by Guest (1997: 270) provides information about the outcomes in the field of HRM. Our results also indicate that the studies related to outcomes in the field of HRM were carried out commonly. The emphasis of Jackson and Schuler (1995: 238) and Ferris et al. (1998: 235) on the importance of context in the field of HRM is also supported by our study.

DISCUSSION AND CONCLUSION
In brief, this study examining the story between the years 1990-2018 in the historical journey of the field of human resources management consisted of four sections. The studies on the evolution of the field, its theoretical foundations and research trends and the limitations of these studies were briefly mentioned in the introduction and literature review sections. In the method and results section, the analyses that guided the study and the results obtained through these analyses are emphasized.
The results obtained within the scope of the study were evaluated under five titles. The first result obtained indicates that the field of human resources does not have a grand theory and the presence of middle range theories efforts formed by the contributions of other disciplines in the field. This indicates that the maturation and evolution process of human resources continues as a scientific field of study. Therefore, it seems difficult to develop a grand theory in the field (Ferris et al. 2004: 231).
Secondly, as in the management sciences and organization theory (Whetten et al., 2009: 1;Oswick et al., 2011: 319;Zahra and Newey, 2009: 1066-1069, human resources also benefited commonly from different disciplines such as economy, sociology and psychology. This is due to the practical nature and eclectic nature of the field. Furthermore, the fact that the disciplinary foundation used by the field is so large reveals a theoretical pluralism in the field. Theoretical pluralism forms both a theoretical richness and a theoretical fragmentation in the field. This duality is likely to trigger methodological discussions in the field (Lengnick-Hall et al., 2009: 77;Ferris et al., 2004: 246-247). Methodological discussions in the field of human resources are outside the scope of this study.
The third result indicates that the field of HRM is dominated by the theories and research trends that take into account macro-micro-analysis levels, internal and external variables and context (Jackson and Schuler, 1995: 244-248;Hendry and Pettigrew, 1990: 25). The results also show that structure-process or structure-actor-oriented theories and research trends with ontological objective and subjective assumptions coexist in the field (Ferris et al., 2004: 246-248). For instance, institutional theory was commonly used in the field with its emphasis on political and economic institutions (macro). Similarly, the creativity theory and cognitive theories that provide explanations at the micro level also affected the field. Furthermore, research subjects considering both non-organizational context and human capital were included in the same studies. Therefore, this situation reveals the presence of an efficient field for establishing links between macro-micro and non-organizational variables in future researches (Wright and Boswell, 2002: 27).
Fourth result of our study is that it reveals a holistic approach in the field of HRM on disciplinary foundation, theoretical foundation and research trends. In other words, the frame related to the general view of the field was revealed by gathering disorganized research trends in the field of HRM under main categories. In particular, the separation of theories on the basis of disciplines and collecting research trends under four titles contributed to this situation. Therefore, our study can be considered as a study that shows the picture of the field of HRM.
The fifth conclusion that can be obtained from the findings of our study provides clues about the evolution of the field in the future. Here, what are the potential theories and research trends that the field of HRM can benefit in the future? was answered. Based on the evaluations made above, the content of future researches can be grouped under three titles: studies considering theoretical development, studies considering research trends, and studies considering methodological problems. The first results obtained show that the field human resources commonly benefited from the resource based view which is considered as the dominant approach of strategic management (Barney et al., 2011(Barney et al., : 1299. Some studies in the literature reveal that the resource-based view received theories and concepts from the disciplines such as economy, sociology and psychology (BağıĢ and Hızıroğlu, 2018;Barney and Arikan, 2001). Therefore, future studies may question whether the theories that form the basis of the Resource-based view will contribute to the field of human resources. For instance, research questions in the forms of how does the implicit knowledge and experience of the management team shape the human resources practices in the Theory of the Growth of the Firm (Penrose, 1959)?, What kinds of differences do the entrepreneurial characteristics specific to the management team cause in human resources practices, policies and functions among firms?, and How can the concept of path dependent contribute to understanding the historical development process of human resources practices in a firm? may promote new studies in the field of human resources.
Similarly, another theoretical framework is the Austrian School of Economics. Based on this theory, the following research questions can be put forward 1-How can the concept of knowledge specific to a certain place and time conditions (Hayek, 1945: 521) explain the practices of human resources depending on the context? 2-What kinds of differences do the subjective evaluations of entrepreneurs on the use of resources (Lachmann, 1956: 2-3) cause in human resources policies and practices among firms? Moreover, the question in form of What kind of contributions can strategies as a practice that discuss the daily practices of people and complement dynamic capabilities studies (Regnér, 2008) make to the understanding of human resources practices? is also likely to contribute to the field. This shows that a relationship can be established between the micro foundations of the strategic management area and the HRM area.
Furthermore, the studies on new institutional economics and context, apart from the theories that form the basis for the resource-based view, seem likely to contribute to the field. According to the new institutional economics, institutions are divided into formal and informal institutions. While formal institutions are defined as law, regulations and rules, informal institutions are defined as norms, culture and ethics (North, 1990: 36-46). Therefore, by considering the inadequacy of the studies on the context obtained from the results of our study in the field of HRM, future studies are likely to contribute to the field from more macro issues within the framework of formal institutions (e.g., discipline of law) and international context. It can be stated that the discipline of anthropology will contribute to the field of HRM other than the strategic management and economy based theories that we have listed so far and which are likely to contribute to the field. The discipline of anthropology may provide valuable information about the effects of cultural differences on the cognitive activities of actors and the reflections of these effects on HRM practices. focus on the effects of internet-based platforms such as online shopping websites, hotel and airlane booking on human resource management (HRM). Similarly, the effects of Marketing 4 (Kotler et al., 2016) on human resources may be discussed in another study. Another question that needs to be investigated may the effects of technological innovations such as virtual reality, human resources analytics, intelligent machines, blockchain, social media, cloud and robotic technology, 3D printer, internet of things, big data, fintech, smart logictics, and cyber security on human resources. Therefore, next studies can discuss the possible changes in the labor market to be caused by the technological advances mentioned and consequently the developments in human resources practices. The studies that will discuss the relationship between digital age and HRM within the framework of what has been written so far related to future research trends may seek answers to these questions: How will digitalization affect the economic and political institutions related to HRM? How digital developments will transform leadership styles and how will this transformation be reflected on human resources? How will digital revolution affect the development of digital capabilities of human resources? How will the HRM curriculum in business schools be shaped in this sense? What kinds of contributions will the digital age make to in-service training and learning processes of human resources in the workplace? What is the role of machine learning in the development of human resources? What kinds of developments will digital developments provide in the control, supervision and monitorability of the operations and processes of human resources? What will be the discretionary power of human resources in job autonomy and control? How will HRM practices evolve and change with digitalization?
Finally, the fact that the field is supplied by so many different disciplines and theories raises a question about which methodologies will be used in the investigation of cases related to human resources. Therefore, future studies can make recommendations about the set of methods and methodology that can be used in the field by making an empirical evaluation about which research methods used in the theoretical studies in the field of human resources.