**4. Conclusions**

Figure 2 shows the frequency of publications from our systematic review over time. This highlights the growing applications of complexity theory in economic research. The trend for the publications included in our systematic review also provides some interesting suggestions on the influence of the global environment and the importance of the contextualization of such events. For instance, the increase in publications during 2010 reflects the impacts of the financial crisis and a moment when academic scholarship further questioned the use of traditional 'linear' economic ontologies. There is also an increasing trend in relevant publications during the last 15 years, with some fluctuations in the most recent period after 2018. This may result because of publications taking their time to get listed on databases.

Table 5 shows which of the reviewed publications have had the greatest impact through citations. The ratio index shows the annual ratio of citations per year, to avoid overly rating the impact of older articles. Hommes (2006) and Tesfatsion's (2006) contributions to the Handbook of Computational Economics have the highest ratios, an indication of the primacy that economics places on these kinds of contemporary quantitative models. Next, in Table 5 are a cluster of several authors publishing in the journal Ecological Economics, a journal that is clearly making an important impact in the integration of complexity theory with macro and meso system modelling that juxtaposes environmental and sustainability issues with the operations of governments and markets. This typifies the interdisciplinary approach of complexity economics. It is also an important observation given the current international concern about climate change and climate warming.


**Table 5.** Yearly ratio of citations—Top 15.

The interdisciplinary nature of complexity theory goes much wider than just this important single journal of Ecological Economics, and the different juxtapositions of other disciplines with economics is evidenced by the range of publication titles in Table 1. The nature of this interdisciplinarity is that it manifests itself especially in sub-disciplinary areas such as business and management studies, and ecology, rather than impacting the historical core of the foundation social science disciplines such as economics, sociology, and psychology. This leaves complexity economics open to the criticism that it is on the periphery of the single discipline. However, conversely the interdisciplinary approaches are contemporary and dealing with current real-world problems and applications. An example is Darnhofer's system model of farm management published in 2014 that deals with how farms can be resilient to ecological and economic change, and it has the fourth highest citation ratio in Table 5. Not all interdisciplinary complexity work is applied across the meso 'connect' and some highly cited scholars attempt an ambitious system world macro view especially when modelling global issues such as sustainability (Balint et al. 2017; Plummer and Armitage 2007).

In the publications reviewed there was a strong presence of ecology and climate change modelling that locate economics in a greater 'world/ecological/global system'. Table 1 evidences this with nine publications coming from Ecological Economics and seven from Ecological Complexity. (The later journal includes important global systems approaches but is less directly related to economics and the analysis of markets). Highly cited examples of the more economics focused approaches in Table 5 include Rammel et al. (2007) and Garmendia and Stagl (2010) and Garmendia and Gamboa (2012).

In terms of metatheory, complexity contributes a stinging critique of earlier economic approaches through its focus on unpredictability (Arthur 2013, 2021; Beinhocker 2006). Linked to this is a revision of economic agents who become not only consumers, but active actors politically, and motivated by a range of social aspects. Agents are therefore seen as heterogeneous and diverse, but with some consistent patterns of behaviour, often manifest in networks. They are not homogeneous. This has influenced the type of modelling that results (Hommes 2006; Tesfatsion 2006; Monasterolo et al. 2019; Balint et al. 2017).

This aspect of complexity, and the acknowledgement of multiple influences on dynamic economic systems, results in numerous publications having a strong ambition to develop meso models that have the potential to include both macroeconomics and microeconomics in some aspect. Here, there is a linking of the levels of analysis (Korhonen and Snäkin 2015; Garmendia and Stagl 2010; Chae 2012). However, this also results in a caution about how the theory is applied. Sometimes applications are speculative and based on general principles rather than offering prescriptive techniques. Good examples are the approaches towards the management of risk in sectors such as finance, engineering, and production (Chae 2012; Naderpajouh and Hastak 2014; Zhu et al. 2017).

Some important conclusions can be drawn about the use of methods in complexity economics. Agent based models and similar theoretical simulations of how a complex economy might behave are popular and often widely cited (Hommes 2006; Tesfatsion 2006). It is surprising that mixed methods and causal configurative methods do not feature more. The best example of such practices being a recent publication that includes Qualitative Comparative Analysis (Gligor et al. 2022). It is the experience of the authors of this systematic literature review that these types of contemporary complexity appropriate methods are used much more in political science, public policy and sociology. Furthermore, in the UK, they have made an important impact on the work of the HM Treasury (Bicket et al. 2020).

The use of general systems models in the tradition of the late Donella Meadows (2008) continue to have a wide use and impact in complexity economics, especially when concurrent with ecological issues (for example, Matutinovi´c 2001; Garver 2019). This is again evidenced from the important impact of the journal Ecological Economics. System models that combine economics with environmental issues also span a wide range of publications including: Cambridge Journal of Regions, Economy and Society, Ecological Complexity, Forest Policy and Economics and The Economic Review of Agricultural Economics.

Overall, there are two key sets of publications that our systematic literature review exposed about complexity economics. On the one hand, there is the scholarship that explicitly addresses recognisable aspects of the contemporary agenda of the economics discipline. We have tended to focus on this literature in the examples used in the thematic analysis. The second area of literature is more implicit in its juxtaposition of complexity and economics, it being primarily concerned with the scientific development of complexity theory. In this second field of publications, the ambitious and wide coverage of complexity science across many disciplines, results in the continuing development of the broad theoretical perspective, but where the application to the working practice of economics is often weak. In our review we have chosen to highlight more the best working examples of the application of complexity science that in our opinion are having the greatest impact on the application and practice of economics. It is our argument that this continues to be an important development and one that will continue to change the nature of economics and its applications. The literature review provided gives evidence for our argument.

**Author Contributions:** Both authors have contributed equally to the article overall, especially with regard to thematic analysis. D.A. led on the PRISMA literature review, P.H. on the introduction and indicative Google Scholar exploration. All authors have read and agreed to the published version of the manuscript.

**Funding:** We are grateful to our employing institutions for their support: University of Brighton and University of Portsmouth. David Alemna's current post is funded by the Economic and Social Research Council [Project Reference: ES/W005743/1], as a South Coast Doctoral Training Partnership Postdoctoral Fellowship.

**Institutional Review Board Statement:** Not Applicable.

**Informed Consent Statement:** Not Applicable.

**Data Availability Statement:** It is possible to reproduce the systematic literature review used in this article, as the search terms are included in full in the text.

**Conflicts of Interest:** The authors declare no conflict of interests.

#### **Note**

<sup>1</sup> The resulting search string: (KEY ("complexity theory" OR "complex system" OR "complex adaptive system") AND SRCTITLE (econ\* OR complex\*) AND ABS (policy OR management OR organization OR finan\*)) AND (LIMIT-TO (LANGUAGE, "English")).

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