Exploring assessment practices of companies actively engaged with circular economy

An emerging research area is dedicated to developing approaches for assessing the ‘ circularity ’ of companies and their products, within the context of sustainability goals. However, empirical evidence on the uptake of these assessment approaches remains scarce. Using a purposive sampling, we conducted a survey receiving 155 responses and held 43 semi-structured interviews with Dutch and Italian companies active in circular economy (CE), pursuing three research aims: to explore the use of CE and sustainability assessment approaches; to study the process of developing assessment approaches; and to uncover benefits of — and barriers to — CE assessment. While we find high variability of assessment approaches, most often, companies develop tailor-made sustainability indicators and apply life cycle assessments to CE strategies. Importantly, assessment development for CE practices requires and facilitates collaboration with external stakeholders. Finally, we reflect on the paradox of standardisation versus tailoring of assessment approaches within the CE reality and recommend establishing company needs and capabilities before designing assessment approaches.


| INTRODUCTION
The circular economy (CE) is proposed as a potential solution to the imbalance of the current linear economic system between limited resource supply and increasing demand for goods (Marino & Pariso, 2020). It has been described as an umbrella concept, building on fields in sustainability science, such as industrial ecology (IE) and eco-efficiency, and aims at retaining value embedded in materials through a series of systemic feedback loops between different life cycle stages (Hobson & Lynch, 2016). Within EU-level policies on sustainable growth, the Circular Economy Action plan plays a key role in the European Green Deal (European Commission [EC], 2019). Simultaneously, CE is growing as a business paradigm (Murray et al., 2017).
Indeed, private sector initiatives are an important driver of the CE transition in many countries, and the diversity of CE business models is increasing (EC, 2020;Henry et al., 2020;Santa-Maria et al., 2021).
In literature, CE is dominated by a corporate and technocentric perspective, aligning CE with current business paradigms, such as innovation and green growth (Calisto Friant et al., 2020;Schoeggl et al., 2020). Perceived benefits for companies implementing CE are related to lowering environmental impacts, realising social improvements and economic benefits, such as cost savings and developments of new markets-or growing existing ones (Laubscher & Marinelli, 2014). Therefore, the putative promise of CE practices lies in reducing negative sustainability impacts without jeopardising growth and prosperity (Ferasso et al., 2020).
While companies are becoming increasingly aware of the potential benefits associated with improving their resource efficiency, the uptake of CE practices is still lacking (Hartley et al., 2020). Translating the concept of CE into corporate strategies is obstructed by various technical and nontechnical barriers, ranging from high start-up costs to the complexity of current supply chains (Jaeger & Upadhyay, 2020). Companies need to develop and apply dynamic capabilities to overcome such barriers and enable the implementation of CE practices (Khan et al., 2020). One of such capabilities, which has not yet received considerable attention in academic literature and is the focus of this article, is that of assessing CE practices and their sustainability impacts (Roos Lindgreen et al., 2020).
This assessment is essential because for many CE solutions and business models available to companies, it is unclear whether-or to what extent-they actually lead to more sustainable outcomes (Blum et al., 2020;Harris et al., 2021). Therefore, in order to contribute towards reaching the United Nations (UN) Sustainable Development Goals (SDGs) (UN, 2017), assessing the sustainability impact of CE practices before implementing them is key. Otherwise, well-intended CE strategies might actually lead to unintended sustainability impacts and burden shifting (Blum et al., 2020;Corona et al., 2019). Indeed, Roos Lindgreen et al. (2021) have found that applying resourcefocused CE metrics in isolation can lead to contradicting results when compared to impacts calculated through life cycle assessments (LCAs).
Different terms for managing units of information are used in academic literature on sustainability or CE assessment, such as metric, variable, indicator, methodology or index (Saidani et al., 2019;Sala et al., 2013;Veleva & Ellenbecker, 2001). Since we aim to capture a wide range of applied approaches from practice, we use the term 'assessment approaches' here. For a company, such an assessment approach includes obtaining data on the sustainability performance of any system (product or company level), allowing for its effective management (Beloff et al., 2004). The obtained information can be used for internal purposes, such as monitoring and evaluating company performance towards the SDGs, but also for external purposes, for example, communication to guarantee compliance with legislation or benchmarking between companies (Bae & Smardon, 2011). While discussing the value of both sustainability and circularity assessment, 1 it is important to remember that for most companies, especially small and medium enterprises (SMEs) which are not required to produce a mandatory sustainability report, these assessments are voluntary activities (EC, 2014). Thus, with limited incentives promoting the assessment of circularity or clarity regarding its integration with sustainability assessment, the motivations of companies to conduct additional assessments remain unknown.
While private sector engagement with CE and assessment approaches for CE from academic literature have been investigated (Kristensen & Mosgaard, 2020;Santa-Maria et al., 2021), empirical evidence on the assessment approaches applied by companies that actively participate in the CE transition is scarce (Hartley et al., 2020).
Furthermore, research gaps exist with respect to the joint application of CE and sustainability assessment approaches, as well as the process of developing them, given the collaborative nature of most CE practices (Brown et al., 2019;Niero & Kalbar, 2019). Finally, the perceived benefits of-and barriers to-CE assessment have also yet to be studied (de Pascale et al., 2020;Rossi et al., 2020). Therefore, we study CE and sustainability assessment practices of frontrunner companies already engaged with CE, which thus are inclined to assess their CE practices. Firstly, we study the practical application of CE and sustainability assessment approaches at company level. Secondly, the process of developing tailor-made CE assessment approaches and the involvement of stakeholders in this process are investigated. Our third aim is to reveal the benefits and barriers of implementing CE assessment. We use an explorative mixed-methods approach consisting of a semi-quantitative survey and semi-structured interviews with companies which are members of national or international CE networks and operating in Italy or the Netherlands. In both European countries, such networks play an active role in sharing knowledge, practices and connecting stakeholders, resulting in a thriving ecosystem of companies engaged with CE (Institut National de l' Economie Circulaire & Orée, 2020). Such networks were thus used within this study to identify a diverse range of companies engaged with CE, both in terms of sector and size.
In the remainder of this article, we present the theoretical background to the study, underlining the addressed research gaps and resulting research questions (Section 2), as well as the mixed-methods approach employed (Section 3), and the results of the survey and interview approach (Section 4). Then, the discussion section amalgamates these results in the context of existing-and future-research directions (Section 5), while the last section offers concluding remarks (Section 6).  Lindgreen et al., 2020;Saidani et al., 2019;Sassanelli et al., 2019).

| THEORETICAL BACKGROUND
These articles describe various assessment approaches and their characteristics, such as their connection to different sustainability dimensions and specific CE strategies. Generally, they focus on the environmental and economic domains, with social elements rarely being considered (de Oliveira et al., 2021). Indicators with an economic focus might be more attractive to business but carry the risk of detaching CE from environmental and social sustainability (Kristensen & Mosgaard, 2020). Furthermore, many indicators are centred around resource use or specific strategies from the 'R-hierarchy' (Potting et al., 2017), a framework commonly associated with CE by companies (Walker, Opferkuch, et al., 2021), making them unsuitable to assess the three-dimensional sustainability performance of circular systems (Corona et al., 2019).
From the wide range of available assessment approaches, we recognise four general categories relevant to companies. First, life cyclebased methods enable the quantification of impacts across all phases of a product's or system's life cycle, from the extraction of raw materials to its disposal (Finkbeiner et al., 2010). A precursor to such life cycle-based methods are material flow analysis (MFA)-based methods, which establish an overview of resource and energy flows across the life cycle of a system (Brunner & Rechberger, 2016 (Kristensen & Mosgaard, 2020). Lastly, and as discussed in the next section, the category of tailor-made indicators, which could be based on a life cycle approach or direct impact, allow for tailoring the CE or sustainability assessment more closely to a company's specific context (Kravchenko et al., 2020). As opposed to life cycle tailor-made approaches, direct impact here refers to 'Scope 1' impacts occurring from sources that are controlled or owned by an organisation (WBCSD & WRI, 2004).
Some authors (e.g. Geissdoerfer et al., 2017;Schroeder et al., 2018) have already stressed that the complex nature of the relation between CE and sustainability affects its assessment. However, a lack of consensus persists on the issue whether CE and sustainability assessment are different or the same and whether one forms part of the other (Vinante et al., 2020;Walzberg et al., 2021 (Pauliuk, 2018). Various other scholars nevertheless regard resource-focused CE metrics as valuable for decision-making and product comparisons (Parchomenko et al., 2019;Sassanelli et al., 2019). It has further been established that, to ensure the quantification of CE solutions' sustainability impacts, existing sustainability assessment methods could be used (Roos Lindgreen et al., 2020;Walzberg et al., 2021).
While available CE assessment approaches for companies are well documented, information on their practical application is scarce (Kristensen & Remmen, 2019;Stewart & Niero, 2018 (Maas et al., 2016). For SMEs, this capability increases when a company develops more sustainable (and holistic) business practices (Witjes et al., 2017). Since sustainability assessment is a field with a longer history, more information on its degree of implementation by companies is available. In fact, sustainability tools, initiatives and approaches, such as corporate social responsibility (CSR) and the GRI, are well known among companies (Lozano, 2020); however, their uptake of CE issues is lacking and less concrete .  . This would also be in line with the long-standing finding in the field of sustainability assessment that indicators should reflect the business realities of a particular organisation; as such, they should not be limited to general methodologies or standards (Keeble et al., 2003). However, there are certain points of reference that could be considered universally applicable, such as the planetary boundaries (Rockström et al., 2009) or the Paris Agreement (UN, 2015). Furthermore, Niemeijer and de Groot (2008) have developed a framework for indicator selection based on causal networks which has found widespread uptake from scholars for discussion with the environmental domain. They point out the importance of looking at the integration of the indicator set rather than focusing on single indicators. Similarly, Addison et al. (2020) propose the creation of an assessment framework for evaluating the biodiversity impact of business practices, and mention the central role of involving stakeholders in the assessment, if the assessment scope goes beyond company boundaries. This is particularly relevant for CE practices, given that they mostly require collaboration of companies within their supply chain network (Brown et al., 2019). Moreover, the involvement of stakeholders in general is described as a methodological necessity for sound sustainability assessment by several scholars (Sala et al., 2013;Troullaki et al., 2021). It is by way of this transdisciplinary involvement that the assessment approaches can be adapted to contextual specificities of the sustainability impacts to be assessed, while also including some standardised indicators based on international consensus (Kühnen & Hahn, 2018).
However, evidence on how companies develop such contextspecific CE assessment approaches is limited in literature (WBCSD, 2018). As in sustainability assessment, one key element in this process is the involvement of stakeholders, especially in connection to the flourishing field of CE consultancies and research agencies that offer CE assessment services (Pereira & Vence, 2021). For example, for public sector organisations, a co-developed CE assessment framework with the active involvement of internal stakeholders has been proposed; it emphasises including sector specifics in CE assessments of organisations (Droege et al., 2021a).

| Benefits of-and barriers to-CE assessment
Considerable research exists regarding the identification of drivers and barriers for embedding CS assessment processes within organisations (Lozano, 2020;Triste et al., 2014). The assessment process is a critical element of strategic management, facilitating and driving change towards CS within a company (Doppelt, 2003;Lozano et al., 2016). Bae and Smardon (2011) (Sala et al., 2015). To complement this, several studies have identified barriers which can be both internal to the company (e.g. lack of awareness on sustainability issues, an absence of perceived benefits, lack of resources), as well as external (e.g. insufficient drivers, complexity of available tools) (Johnson & Schaltegger, 2016;Lozano, 2007). The identification of barriers enables the development of corresponding capabilities, allowing companies to not only overcome these barriers, but to go further than only compliance (Hart, 1995;Khan et al., 2020). In addition, the identification of barriers supports the revision of assessment approaches themselves to improve their applicability and relevance to companies.
For instance, evidence points towards SMEs experiencing more significant barriers to sustainability assessment (Jaramillo et al., 2019;Johnson & Schaltegger, 2016), which has led to the development of new or modified assessment approaches for smaller companies (Garza-Reyes et al., 2018;Global Reporting Initiative, 2018). These advancements are essential as SMEs represent more than 99% of all companies in the EU (Eurostat, 2018 3 | METHODS Figure 1 illustrates the mixed methods approach (Creswell & Plano Clark, 2018) consisting of two complementary research methods to obtain insights from frontrunner companies engaged with CE: a semiquantitative survey and semi-structured interviews (Adams, 2015).
We chose the combination of these two methods to identify the approaches that were applied (through the survey), and how and why companies applied these approaches (through interviews). It should be highlighted that the survey and the interviews contained additional questions analysed in the context of a separate study (Walker, Opferkuch, et al., 2021).

| Sampling procedure
To identify companies actively engaged with CE practices in Italy and the Netherlands, we applied a purposive sampling method (Hibberts et al., 2012). Namely, we only included companies which are members of existing national and international CE networks since we assume they are frontrunners in CE and its assessment. A list of the included CE networks can be found in Appendix A. In order to be included in the survey, besides being part of a CE network, respondents needed to satisfy two other criteria: being a private sector organisation, according to national law; and having an official website. The survey was delivered through the online survey tool SurveyMonkey (2021) calls. Both the survey and interview participants were aware that the results of the study would be anonymised.

| Sample description
The survey was sent out online to a total of 809 companies and was fully completed by 155 (survey response rate: 19%). Of the responding companies, 46% were based in Italy and 52% in the Netherlands. Two respondents were part of Italian or Dutch CE networks while being based outside of these countries: one from Luxemburg and one from Austria. In the interviews, the distribution of companies (n = 43) was nearly the same, with 20 companies based in Italy and 23 in the Netherlands.
The companies were subdivided into the Eurostat classification scheme for SMEs. For the 155 survey companies, 45% consisted of micro companies (1-9 employees), 33% of SMEs (10-249 employees) and 22% of large companies (250+ employees). For the 43 interviewed companies, this was almost the same, with 49% micro companies, 26% SMEs and 25% large companies.
The respondents categorised their company sectors themselves according to the statistical classification of economic activities in the European Community (NACE) (Eurostat, 2008). Though both samples were diverse, Figures 2 and 3 show that the most frequently named sector in both cases was 'Manufacturing', followed by 'Other service activities' and 'Professional, scientific and technical activities', both of which represented consultancy companies. Whereas the former category would actually be assigned to repair services, the analysis of individual survey answers revealed that several companies in this category were in fact consultancy companies. As to be expected, 'Waste & water management' companies were also present in the sample, given the inherent circular qualities of their business models.
Finally, Figures 4 and 5 prove that the survey and the interviews collected information from decision-makers with generally high authority and knowledge on the topic of sustainability and CSR. Interestingly, in the interviews, the share of respondents from the 'General management' and 'Sustainability & CSR' was notably larger than in the survey, representing a higher willingness of these respondents to discuss sustainability and CE-related matters.

| Survey development
For a detailed description of the creation of the overall survey and its distribution to 809 companies, readers should refer to Walker, Opferkuch, et al. (2021). Regarding the survey questions addressed in this paper, we first asked companies whether they regarded a list of assessment approaches as either CE or sustainability assessment and whether they applied them on a company or product level. The identification of CE and sustainability assessment approaches was based on literature (Corona et al., 2019;Ness et al., 2007;Sala et al., 2013;Vinante et al., 2020), as well as input from a sustainability consultancy specialised in life cycle-based assessments. As identified in Section 2, the assessment approaches were categorised into life cycle-based/ footprint, reporting frameworks, tailor-made indicators and single indicators, depicted in Table 1.
We also asked what system boundaries companies considered when doing assessments and whether they had developed their own assessment systems besides those postulated by the authors. In case companies had developed their own assessment frameworks, we fur-

| Interview guideline development and process
To get a better picture of how frontrunner companies engaged with CE practices develop assessment approaches and why they do (or why they do not) implement these, we conducted interviews with 43 respondents which ranged between 45 and 90 mins. The interview questions focus on companies' understanding of CE and sustainability assessment, the assessment creation and application, and barriers and

| Data analysis and integration
After the survey was closed, we exported the answers from SurveyMonkey into the statistical analysis software IBM SPSS Statistics 26 (IBM, 2020). Then, we took a univariate analysis approach and analysed the descriptive statistics. To identify whether variations in the answers correlated with the size (micro, small to medium and large) as well as the sectors (divided into production and service sector) of the respective companies, we employed cross-tabulations (Bartiaux et al., 2018) and conducted a contingency coefficient test to determine the significance of the correlations.
Regarding the interviews, we jointly analysed the interview notes in the qualitative data analysis software NVivo R1 (QSR International, 2020) with an inductive coding approach based on thematic analysis (Braun & Clarke, 2006). After assigning codes to the responses for each sub-question, we compiled them into major themes, as presented and discussed in the following sections. This inductive approach was chosen following the (1) novel nature of the research topic, and the inherent conceptual ambiguities between sustainability and CE, as described in chapter 2, and (2) the scarcity of empirical evidence on company engagement with CE assessment. Lastly, for a comprehensive analysis, the findings from the survey answers were confronted and complemented with the findings from the interview responses in an iterative manner.

| RESULTS
This section presents the results according to the three main research questions formulated in Section 2.

| Application of assessment approaches
As seen in Figure 6, the application rate of the 22 approaches, previously introduced in Table 1, shows large variability, both overall and within each of the categories. Generally, 36% of companies have not applied any of the approaches on either a product or company level.
On the product level, 53% of respondents do not apply any approaches, 7% of respondents apply one approach, and the remaining 40% applied two or more approaches. Looking at the frequency of approaches applied at company level, 46% of respondents do not apply any approaches on a company level, 10% apply only one approach, and the remaining 44% apply two or more approaches. While the application of assessment approaches is in most cases not entirely attributable to either company or product level, there are some cases where differences were observed which may relate to the intended goal of these assessment approaches. The GRI standards, designed to help companies assess and report their impacts, are applied by >80% on company level. The same holds for EA (75%) and for tailor-made sustainability indicators with direct impact (75%). E-LCA is, on the other hand, applied by around 70% of companies at the product level, signalling a high application rate within the sample.
Appendix C (Table C1) provides more insights on the level on which the other approaches are applied.
The companies were also able to leave comments with respect to their assessment of sustainability and CE. Several pointed out that company size and sector were important determinants when applying a certain approach or not. Therefore, the relation of both company size (micro, SME, large) and sector (production or service) with assessment application has been analysed. The complete results of this analysis are presented in Appendix C (Table C2). After performing Pearson chi-square tests, the correlation results between company size and CF, LCA and GRI showed statistical significance ( 4.2 | Development of CE and sustainability assessment approaches

| Stakeholder involvement
The companies answering the survey indicated that 39% of them did not create their own assessment framework, 24% have developed their framework internally, and 27% worked with external partners (Figure 7). Slightly less than half of those external stakeholders were consultancies (16), followed by universities (12) and other partners (11); also, several survey respondents involved more than one of these stakeholder groups. We further addressed the assessment development process and the inclusion of stakeholders in the interviews.
In a first step, interviewed companies mostly consulted internally with their employees. Frequently included stakeholder groups were suppliers with which companies had close relationships, clients and universities.
Companies had different forms of collaboration with these groups.
The initiative to create assessments usually came from larger companies in the supply chain. Their collaboration with the 'preferred suppliers' was sometimes based on joint method development, but more often on delivering data regarding the sustainability impacts of upstream production steps. Companies' clients were the second largest group that influenced corporate assessment practices by, for example, stipulating certain certifications or indicators to be reported in the tenders the respondents were bidding for, such as Environmental Product Declaration, SA8000 or ISO 14001. Companies also considered the clients' needs and knowledge of software tools when opting for a certain assessment procedure. Following this, for companies with a larger product portfolio, assessment was described as more complex. Conducting client workshops was a frequent approach to identify their needs with regard to the companies' impact assessment. Finally, universities were often involved to either jointly develop an assessment methodology or to verify the scientific rigour of the assessment process.
Consultants were at times hired to support the assessment process, both through tool development and assistance with its implementation. This collaboration allowed the consultants to continuously adapt and improve their assessment methods. Furthermore, consultants also provided expert knowledge regarding life cycle inventory data of secondary materials used as production inputs.
Finally, larger companies in particular were working on standardising assessment approaches within industry groups such as Factor10 of the WBCSD or the CE100 by the EMF. While they themselves did not develop the tools, they conducted pilots and provided feedback to the working groups. In contrast, smaller companies often did not assess their activities in a quantitative manner but had an open ear for feedback from their clients and employees, as to align their activities with their often-idealistic corporate values.

| Assessment needs and preferences
Overall, respondents indicated that expert input would be moderately beneficial throughout the assessment phases listed, except for 'Internal communication of results'. Even though the need for expertise was similar in both sustainability and circularity phases, Figure 8 shows it was considered slightly more beneficial for the F I G U R E 8 Benefit of expert support for sustainability and circularity assessment, by company size (n = 101) [Colour figure can be viewed at wileyonlinelibrary.com] implementation of circularity assessment approaches than for sustainability assessment approaches.
We also found that large companies had a considerably lower need for expert involvement than SMEs and micro companies. It was further observable that the spread between benefitting from help between circularity (higher) and sustainability (lower) assessment was the highest within large companies, while SMEs and smaller companies seemed to potentially benefit more evenly from both circularity and sustainability assessment support.
When contrasted with the interview findings, it is interesting to observe that micro companies simultaneously form part of the group of companies which seem to potentially benefit the most from external assessment, while also considering assessment in general as superfluous.
With regard to the development of future CE assessment approaches, almost half of the respondents designated the supply chain to be the most suitable level for assessment, given the collaborative nature of CE practices. However, it was also acknowledged that this might be too complex, especially for large companies with an extensive portfolio of products and their respective supply chains.
About a third of interviewees proposed that the level of assessment should be adapted to the context. A similar number of respondents advocated for employing an assessment on organisational level, especially if a company provided services or included internal supply chains. Yet, again, it was argued that companies were already using several assessment tools on an organisational level, so adding more might not always be favourable nor feasible, especially in the case of a diverging product range. The product level was suggested by about a quarter of companies, with the proposition that metrics should be clearly measurable and not subjective. According to them, it was easier to establish a product's rather than a company's degree of 'circularity', given there was no clear benchmark against which to compare company circularity. Other levels proposed included project level, mainly raised by construction companies, the regional, business group or portfolio level.

| Benefits of-and barriers to-circularity assessment
The 30 interviewed companies which stated that they implemented some form of CE assessment discussed the perceived benefits they obtain from this assessment. Respondents could mention more than one benefit, and through the inductive coding process, each benefit was grouped into one of two domains: (1) external communication and collaboration or (2) internal improvements and insights. The most frequently mentioned benefits are presented in Table 5.
Generally, the interview participants discussed how conducting some form of CE assessment has benefitted their marketing and external communication processes with stakeholders and clients in particular, as the results demonstrate the value of adopting CE strategies. Internally, responses highlight that for the companies, the entire CE assessment development process resulted in a positive learning experience, rather than from only receiving the final assessment result. Interestingly, investors were only mentioned once with relation to the benefits of CE assessment, suggesting that in its current form, CE assessment approaches are not necessarily integrated within management-level decision-making. In addition, several participants indicated that although through CE assessment they have been able to improve collaborations, the assessment process always needs an initial goal: 'Are we measuring CE to involve different members of the chain or are we measuring for the sake of measuring?' (micro company, other services sector).
The 13 companies which stated that they did not conduct any type of CE assessment then elaborated on the 15 main barriers encountered when considering implementing a CE assessment approach, presented in Figure 9. Through the inductive coding approach, two key categories of barriers became apparent within the interviews: (1) internal and (2)  to conduct yet another kind of assessment was limited. This was emphasised by the fact that it was unclear how the assessment results would be used, making it more difficult to justify allocating resources.
Within these responses, no correlations were observed between company size, sector or country and their respected barriers and/or benefits.

| DISCUSSION
Overall, around a third of the companies in the survey sample do not conduct any CE or sustainability assessment. Also, as previously iden- . We also found that companies in the production sector were significantly more likely to implement LCA and three single indicators related to resource flows (RR, RC and VWdL) which could be explained by the higher importance of such flows in companies which are transforming materials into products. In contrast, companies in the service sector, which are more often working with intangible products, might apply different CE strategies, subsequently resulting in different impact assessment needs (Blomsma et al., 2019).
With respect to CE and sustainability assessment, findings here show that for companies, the distinction between the two is not clearly defined. This is in line with the persisting blurred perspectives F I G U R E 9 The seven internal and nine external barriers to CE assessment identified by companies not conducting any form of CE assessment. The four external barriers shaded in grey form the subcategory of methodological barriers (n = 13) of the two paradigms from both companies and academic literature (Schoeggl et al., 2020;Walker, Opferkuch, et al., 2021). Most assessment approaches were considered by survey participants to be useful to assess CE as well as sustainability. Yet, from the interviews, twothirds of respondents perceived CE assessment as a part of a wider sustainability assessment, where the latter encompasses the social dimension as well as certain environmental aspects which interviewees considered being not directly related to resource use (e.g. CO 2 emissions and energy use). Some companies with CE 'in their DNA' equated their general performance assessment with CE performance. However, as various authors have indicated, CE practices do not always lead to improved sustainability impacts (Blum et al., 2020;Corona et al., 2019). While our research demonstrates the confusion companies have regarding the differences and similarities between CE and sustainability assessment approaches, the majority of interviewees agreed that sustainability takes precedence over CE, as is promoted in other studies (Kristensen & Mosgaard, 2020).
Regarding tailor-made approaches, a small majority of companies in our sample that developed assessment approaches have collaborated with external parties, primarily consultancies, but also universities or supply chain partners. In such collaborations, consultancies and universities often provide knowledge, in line with Pereira and Vence (2021). Consultancies often help companies to adapt existing assessment approaches to corporate realities and to generate information for decision-makers. Furthermore, the consultancies also use their assignments to improve their tailor-made methodologies. Meanwhile, supply chain partners are mainly involved for data collection. This draws attention to the ability of CE strategies to increase collaborations along the supply chain (Brown et al., 2019). At the same time, closer collaboration is needed to address the existing disconnect between research and practice with respect to assessing (the sustainability of) CE practices (Harris et al., 2021).
In the development process, larger companies often make use of available frameworks which support mandatory reporting, such as the GRI as well as tendering requirements made by their governments or clients. While using existing frameworks can be considered a topdown approach to developing assessment approaches, the involvement of stakeholders enables a bottom-up co-creation of assessment approaches, potentially resulting in enhanced assessment capabilities.
This reflects two established findings from sustainability assessment literature: (1) Tailor-made assessment approaches better reflect companies' business realities, and (2) the involvement and participation of stakeholders is crucial for the development and application of assessment methodologies (Maas et al., 2016;Sala et al., 2013). Regarding the requirements for external assistance when developing CE and sustainability assessment approaches, we find that the company's expectations are similar for both CE and sustainability assessment. This indicates there is a similar level of understanding of the two concepts, although some tendencies stood out. Primarily, companies indicated they need the most external support when deciding how to combine circularity and sustainability indicators as well as to model the impacts of their CE practices. The latter is also one of the most challenging phases documented in literature, especially for SMEs not experienced with impact assessment methods of life cycle-based/footprint-based assessment approaches (Chevalier et al., 2011). Interestingly, external expertise was considered least beneficial for internal communication within the survey, whereas internal improvements and insights were established as major benefits of CE assessment in the interviews.
This study, to our knowledge, is the first to identify the benefits of and barriers to CE assessment within the private sector. Within the interview sample, three-quarters of companies declared that they conducted some form of CE assessment, while the remaining onequarter did not. The latter group pointed to seven internal and nine external barriers to CE assessment, a categorisation of barriers that has previously been found in literature on sustainability assessment.
Some of those barriers were categorised as methodological issues, related to the current absence of any standard or benchmark for CE assessment. Companies explained that this has resulted in a lack of demand or general awareness for CE assessment from clients, as similarly found by Droege et al. (2021b). Interestingly, for the companies that had implemented some form of CE assessment, the primary benefits concern the internal optimisation of CE strategies and the use of CE assessment results within marketing and external communication.
This result highlights the value companies obtain from the overall learning process associated with developing and implementing CE assessment, as companies were able to further integrate CE within their CS and strategic management processes, as is expected by Skaerbaek and Tryggestad (2010) and Lozano (2015). Additional benefits of CE assessment, such as increasing transparency and identifying opportunities for collaboration, were in line with the general benefits of sustainability assessment a company will experience, as described in Bae and Smardon (2011).
With respect to most of the internal barriers to CE assessment we identified (e.g. small company size), our findings suggest that they are consistent with general barriers to sustainability assessment approaches, as seen in Jaramillo et al. (2019). This suggests that ongoing efforts to develop a single standard for CE assessment, e.g. by the ISO/TC 323 (ISO, n.d.), will not remove all barriers to CE assessment. This highlights the continued importance of acknowledging existing barriers to assessment within sustainability research; future CE assessment approaches must consider them in order to increase the accessibility of sustainability assessment in general, as opposed to amplifying assessment fatigue (Khalid et al., 2020). Our study also reveals the limited assessment capacities of SMEs, as already established in previous studies (Johnson & Schaltegger, 2016), and stresses the benefits of CE assessment with the hopes that SMEs and micro companies can be informed and supported to allocate resources for this endeavour.
Finally, the results of this study call for a reflection on a longdiscussed paradox associated with assessment: standardisation versus tailoring of assessment approaches. First, as already mentioned, our results showed a key barrier for companies to conduct CE assessments was a lack of relevant benchmarks or standards, prompting a call for some form of standardisation of CE assessment and reporting.
However, we have found that companies obtained numerous benefits through the process of developing tailor-made CE assessment approaches, benefits which would be potentially reduced, if standardisation was to occur in an overly prescriptive way. At the same time, it is important to acknowledge that companies selecting their own CE indicators opens the doors for incidences of greenwashing, as observed in recent studies on CE assessment and reporting guidelines Pauliuk, 2018). These studies indicated that companies are able to cherry-pick CE indicators, reporting more on aims and intentions, rather than actual performance. In response to this, we refer to the suggestions of previous studies including Kühnen and Hahn (2018), who discussed this paradox within the context of social sustainability assessment. The authors suggest that while a normative consensus is emerging on what kind of indicators are to be included, decision-makers have to accept that at least part of the assessment results will remain incomparable, but are adapted to the respective context (Kühnen & Hahn, 2018 (2001) suggest the use of core and supplemental indicators, facilitating both comparability of performance and flexibility for context-specific aspects, a suggestion which could be utilised within the context of assessing CE practices.

| Recommendations for academia
While academia was swift to propose a ubiquity of assessment approaches designed to assess circularity, sometimes explicitly identifying their relation to sustainability, less robust knowledge has been developed on the topic of assessment benefits. How the assessment process and results are used for strategic decision-making should be further investigated to direct the development of assessment practices. Moreover, such assessments often require expert knowledge and data that might not be readily available in the private sector.
Therefore, we recommend that scholars should attempt to create CE assessment approaches with benefits that are validated by their end users (companies), as to facilitate their uptake. For this, a clearer picture of company needs and capabilities is required to design assessment approaches that match business realities, as has been the case for sustainability assessment. For example, companies expressed they would appreciate, if CE assessment were to include the whole life cycle or product supply chain, which implies the involvement of a wider set of stakeholders. When designing CE assessment approaches, it is thus essential to include not only the immediate stakeholders of companies, but to ideally involve the actors involved throughout the entire life cycle of the companies' products. While this has also been advocated for in sustainability assessment (Sala et al., 2013), the life cycle perspective inherent in CE provides a comprehensible and accepted rationale for the co-creation of CE assessment approaches. It could be the role of scholars to facilitate the joint development of assessment approaches that help to identify and involve such stakeholders, promoting the integration of participatory processes, while ensuring that interests beyond the businesses' stakes are covered (Keeble et al., 2003). Future studies could also integrate such participatory processes for assessment development in fields not directly related to CE, such as innovation and strategic management studies.
Finally, we recommend that academia should be clear in disseminating the message that CE is best used as a means to achieve sustainability and that assessing circularity in itself would not serve this purpose. While circularity and sustainability indicators tend to overlap in some instances, assessment should be able to reveal whether a CE practice will make a company and its partners more sustainable or not. Nevertheless, we argue that CE assessment can still provide companies with insights valuable to managing their resources; it could be seen as a precursor of and not a substitute for sustainability assessment. After all, to assess the impact of resource flows on sustainability, these flows first need to be identified and quantified. For this, we recommend incorporating the use of existing assessment approaches such as MFA-based methodologies, instead of promoting the development of new assessment approaches from scratch (Birat, 2015;Kalmykova et al., 2018