The Trust Dividend
28th September 2021 | Mark Hollyoake, Dr Melanie Ashleigh and Professor Malcolm Higgs
The strategic implications of trust building in B2B client relationships and the way towards enhancing them to create mutual economic value.
There is a noticeable lack of clarity around the construct of trust in the business to business (B2B) context. The thesis on which this article is based considers how trust building antecedents operate dynamically within a B2B relationship, and how they can be used proactively to help develop trusting relationships.
It deployed grounded theory qualitative research undertaken through a focus group, feedback workshops and 37 semi-structured interviews utilising critical incidents as units of analysis. The interviews were multi-level (inter-organisational, inter-team and interpersonal) between dyads.
The findings evidenced cognitive and affective dissonance occurring when relational intentions failed to meet expectations, engagement and experience that both sides intentionally set out. The thesis also evidenced B2B relationships being strategically driven from an organisational level through relational intent and the establishment of mutual relational benefits. Finally, the thesis addressed where trust resides in B2B relationships between both sides and levels. At organisational level, trust resides in the moral bonds that have achieved a cultural quality.
This thesis, therefore, contributes to the body of literature and theory in B2B trust between two organisations in a relational context in the following areas:
- Firstly, it contributes to understanding the importance of relationship intentions, as opposed to commitment, at an organisational level, highlighting the strategic mediating effect of the cross-dyad role through the relationship intentions. Additionally, the thesis highlights both commitment and communication as important antecedents of B2B relational trust at group/team and interpersonal level, as intention moves from intangible to tangible action between both sides of the relationship.
- Second, the study confirms the proposition made by social exchange theory that emotions and feelings play a role in business relationships, which involve social exchanges as evidenced in the role of affective trust expansionist/reductionist antecedents between both sides of the relational dyad. The theory of dissonance and consonance that incorporate two different groups of characteristics (affective/emotional and cognitive/rational) with a reductionist and/or expansionist effect on B2B relational trust is also developed.
- The third contribution identifies trust residing at organisational level, manifested through: moral bonds (cultural), action and behavioural conceptualisation, shaped through the development and signalling of relationship intentions. At an operations, group, team and interpersonal level, the contribution builds on structuration theory, demonstrating that trust resides at these levels as a manifestation of artefacts (relationship charter/mission/vision) standard norms (contracts, processes, systems and ways of working) and cognitive social stuff in the effective memories of the relationship agents/actors.
- Finally, a model of B2B relationship trust development contributes to academic research and new knowledge. It does this by developing an intention-ability-credibility-interdependence-mutual value outcomes–time framework that works across all organisational levels and between dyads. It builds on the definition of B2B trust and sheds light on how both sides of the relationship can work proactively to use trust to enhance the relationship.
Trust is recognised as a central concept in relationship marketing (Blois 1999) and this may be attributed to the significant impact on many outcomes in this area (Seppanen, Blomquist and Sundquist (2007).
This paper considers the strategic implications of trust building in B2B client relationships, the way trust-building antecedents operate dynamically within B2B relationship and how they can be used proactively to help develop trusting relationships between two businesses to co-create mutual economic value. It sets out and answers the research question:
What are the mechanics and dynamics of trust building within B2B client relationships, and how can this understanding be applied proactively to enhance client relationships and create mutual economic value?
The key research objective is to determine the dynamics of trust building in B2B customer relationships at interpersonal, inter-team/group and inter-organisational levels and, through this understanding, identify how to apply the dynamics and how they enhance customer relationships. This overall objective then frames the more specific objectives outlined in this section. When viewed graphically (Figure 1), trust is placed first, which influences the relationship affecting the performance.
Trust research employs a diversity of methods, disciplines and traditions (Lyon et al, 2012b). Lyon et al (2012) proposed that, as research on trust matures, this creates an opportunity to consider the innovative developments by trust researchers into the methods they have used in order to examine this concept. These have been taken into consideration, discussed and evaluated prior to identifying and selecting the grounded theory (GT) method and critical incident technique (CIT) approach in the thesis to collect, codify, analyse and generate insight. The methodology developed and deployed involved firstly a focus group and then qualitative interviews.
Treatment of qualitative data
In this study, the unit of analysis is the level of an organisation between both sides of the relational dyad. Specifically, this represents the relationship between one company (supplying company) at a defined level (ie, interpersonal, inter-team/group, inter-organisation) and another company at a defined level, which in the case of this research is an actual customer of the supplying company. This aligns with the research aim, objectives, questions and purpose of this study that focuses on understanding B2B relational trust and its role between the dyad at multiple levels.
This study focuses on the identification of critical incidents in the relationship(s) (Flanagan, 1954) between both sides of the relational dyad at multiple levels developed through the application of CIT. This is developed through the deployment of grounded theory and semi- structured interviews as a way to unlock the incidents to develop initial codes for analysis (first-cycle codes). In this study, the respondents (the unit of measurement of the critical incidents) represent the three levels of the organisation(s) being researched:
- Informants from organisational/leadership level who are knowledgeable about the relationship the two organisations have at an organisation-to-organisation level, and how the other levels interact with the leadership/organisational level.
- Informants from the team/group level who are knowledgeable about the relationship between the two organisations at this level, as well as their relationship with the other levels.
- Informants from the staff/personal level who are knowledgeable about their one-to- one relationship with the other organisation and the other levels.
At organisational level, trust resides in the moral bonds that have achieved a cultural quality.
This provided the research with respondents and informants covering the three levels of the relational dyad on both sides of the organisation. Previously, many studies into business relationships have focused on the supplier side of the relational dyad (Barnes et al, 2007; Joshi, 2009). In other instances, data were collected from informants with a more functional responsibility (Rindfleisch and Heide, 1997). These include sales managers (Anderson, 1985; 1988; John and Weitz, 1988; 1989), purchasing managers (Heide and John, 1990; Noordewier et al, 1990), or agents’ intermediaries (Anderson and Narus, 1992). This research extends the reach of the informants in the relationship between two organisations used previously, to include project managers, customer services, administration, finance, information technology, operations and respondents from three levels in each organisation (personal, group/team, and leadership/organisational).
Focus group participants and recruitment
The participants were selected using purposive sampling (Hair et al, 2009) on the basis that they occupy or have occupied a senior position within a B2B organisation within a customer-facing role. They represent a diverse number of sectors: outsource services, pharmaceuticals, wines, beers and spirits, fast-moving consumer goods, and information technology services.
The seniority of the participants helped to achieve a multi-level view of trust within B2B relationships. Zaheer et al (1998) argued that the leadership team can reflect the action conceptualisation of trust through their intentions, actions, behaviours, attitudes, reality of the actions and the effect they have both internally and externally. Furthermore, the experience and roles of the group also offer the potential to provide insights into the group/team and interpersonal levels of trust in B2B relationships.
The sample drawn upon consisted of 37 interviews: 18 interviews with representatives from selling-side organisations and 19 interviews with representatives from buying-side organisations. The respondents represented organisations from the following sectors: financial services, fast moving consumer goods, outsourced information technology services, utilities, pharmaceuticals, and retail. Each organisation and key contacts were known to the researcher through longstanding professional relationships. They were approached in the initial thesis concept stage (research proposal), where the research aims and objectives were shared and potential organisational insights for relational improvement discussed.
Relationships explored during trust research
- Relationship 1. Financial services organisation to a key intermediary: the relationship has existed for over five years, is mature, and the exchanges represent a combination of channel marketing and distribution.
- Relationship 2. Pharmaceutical organisation to a key wholesale/retail/hospital organisation: the relationship has existed for over ten years, is mature, and the exchanges represent a combination of supply chain, channel partner and specialist service provision.
- Relationship 3. Fast-moving consumer goods organisation to a multiple retail grocery company: the relationship has existed for over 15 years, is mature, and the exchanges are across multiple categories, facia formats and locations at a shopper/consumer level.
- Relationship 4. Outsourced technology, information and data organisation to a key utility provider: the relationship has existed for over five years, is maturing, and the exchanges represent the provision of contracted services across multiple functions, departments and sites.
Research participant procedure
All the interviews took place face to face, and extensive notes were taken during each interview. All of the interviews were audio taped and transcribed verbatim. Only four interviews were not recorded, due to internal security procedures and regulations. In this instance the handwritten notes were transcribed. Each side of the relationship was represented and had respondents from all three levels of organisational structure: leadership level – inter-organisational, management level – inter-group/team, and operational/activation level – interpersonal. The interviews followed a semi-structured approach, in each instance of the fieldwork.
This thesis contributes to understanding through highlighting the importance of relationship intentions, as opposed to commitment at an organisational level.
Working with the data corpus
The data were coded in two separate stages in order to demonstrate the objectivity of both the approach and development of the first-cycle and second-cycle codes. This provides the objective platform for emergent theory development. The data were collected from two primary sources: focus group and research partner interviews.
The first stage involved transcribing the focus group session from a recording of the entire event conducted with eight respondents into a Word document. This provided the researcher with the opportunity to listen to and compare the transcript to the notation taken in parallel as the fall-back plan to check for validity. During this process the narrative was coded to each participant in a way to ensure anonymity yet allow analysis of the respondent’s answers within the focus group session. The second step involved loading the transcript into NVivo.
An initial word-frequency query provided insight at a high level and a cross-check against the focus group common themes that emerged from the session. This allowed the first-code generation. At this step, the focus group transcript and themes were shared with two independent observers to verify the initial themes and a less than 10% divergence was observed, validating the approach. The third step involved transcribing the 37 digitally recorded interviews into individual Word documents. These were individually coded to allow respondent analysis – ie, by level, by supplier/customer – while retaining individual and organisational anonymity.
Developing the initial codes
Systematic interrogation of each transcript of the interviews was undertaken to identify themes that related to the focus group and critical incidents that surfaced in the interview. Specific coding approaches were selected and developed based on “fit” to the subject and qualitative nature of the research. Three methods were deployed at this stage: initial coding, invivo coding, and process coding.
The next stage involved searching for themes across 175 codes in two discreet steps, one of which offers a new methodological approach to qualitative research.
To explore the total data corpus for code frequencies for qualities (Saldana 2016), the data corpus was split into the two sides of the relationship – buyer/suppliers – and code frequency was once again used to explore the data for qualities within and between the two datasets.
At organisational level, trust resides in the moral bonds that have achieved a cultural quality.
The next step was reframing the data corpus to reflect the level of respondent. The research was organised and conducted to reflect the different levels/structure in both sides of the relationship: leadership – inter-organisational level, management – inter-team/group level, and staff – interpersonal level. At this level, the analysis focused on variance between levels and across the dyad, “what’s working” and “what’s not working” at each level, highlighting and captured as code charting (Harding, 2013). This led to the identification of 14 trust-building themes and 16 trust-diluting themes.
Reviewing the initial themes
Focused coding: This searches for the most frequent or significant codes to develop the most salient categories in the data corpus. Focused coding is seen as appropriate for virtually all qualitative studies, but particularly for grounded theory methodology, and the development of major categories of themes from data. Using the lens of focused coding in conjunction with theoretical coding applied to the 30 themes emanating from the bridging process led to amalgamation of the 30 themes into:
- Four core themes – cognitive dissonance, affective dissonance, cognitive consonance, and affective consonance.
- Five supporting themes – relational intention, relational ability, relational credibility, relational interdependence, and relational mutual benefit.
- Two linking themes – relational commitment and relational communication.
Findings and discussion
Overall, this thesis supports and evinces the role of trust as a key concept for relationship development or dilution, so influencing B2B relationships at multiple levels is supported. This confirms the findings of previous studies, which show the effect of trust on relationship outcomes – ie, strategic information sharing, cooperative behaviour and relationship benefit (Hammervol and Toften, 2013; Ashnai, 2014; Dowell, 2015) – and develops further by showing the role of dissonance (cognitive/affective) and consonance (cognitive/affective) on relationship trust development and its mediating effect (Figure 2).
The strategic nature of relationship development through the relationship intention is evident as a vision and mutual value opportunity. This leads to positive mutual change outcomes that motivate the relationship at an organisational level. The role of commitment in this instance has a secondary/supporting role aligned with mutual value, relational intent and understanding each other. The role of commitment in relational development and trust building was found to be counter to the work of Morgan and Hunt (1994), Palmatier et al (2007a), and Ashnai (2014), who found commitment as having a central role in determining relationship outcomes. This is an organisation-level specific finding from this study that adds to and builds on organisational-level trust-building.
The distinctions between cognitive and affective trust were confirmed, in line with previous studies, (Dowell, 2015; Akrout, 2017) by showing and discussing their different impacts, roles and outcome constructs in B2B relationships. However, this thesis goes further by exploring cognitive and affective trust as the foundational elements of B2B relationships and how it affects performance negatively through dissonance and positively through consonance. This develops and contributes to B2B relationship theory in trust development, through the demonstration of the expansionist effect of affective and cognitive antecedents when applied in consonance and the reductionist effect of affective and cognitive antecedents when applied in dissonance.
The relationship establishes intention as the initial B2B relational trust trigger at organisational level. It operates between both sides, setting out intangible trust expectation “vulnerability” and the engagement required to turn the intangible trust into tangible trust. This is the first stage in the model presented in Figure 3. Relational intentions can be attributed to a new relationship or to the continuation of an established relationship.
When operating in an interlinked nature, the six elements depicted in Figure 3 contain the potential to positively build relational trust through an expansionist effect or to negatively dilute trust through a reductionist approach. Ashnai (2014) posited a relationship framework of attitude-behaviour-outcome in business relationships. This thesis goes further in establishing intention – ability/credibility – interdependence and mutual benefit as a relational framework for business relationships. Furthermore, the role of relational intention has a strategic mediating effect at inter-organisational level. Anderson and Weitz (1992) contended that a business partner may undertake an action that demonstrates good faith and binds the channel members to the relationship, affecting the perception of the other party. In this case, Anderson and Weitz (1992) discussed the actualisation of a relational intention that moves from intangible to tangible (Mollering, 2002).
However, in a later work, reference is made to relationship intention: “Businesses send signals that they intend to work together with channel members over the long run.” “These signals help build the level of mutual trust in a dyad.” (Anderson and Weitz, 1989, pp. 314,315) Relational intention was also found to have a mediating effect at the inter-group level in framing the joint working, co-creation and ways of working to turn the intention into reality. At interpersonal level, the relationship intention operates on an affective level reflecting the attitude, commitment and expected effect (mutual value) from interpersonal interaction between the dyad.
The thesis demonstrates that inter-organisation, inter-team/operations and interpersonal trust are three distinct constructs through showing how they interact between the dyad at the three levels. Doney and Cannon (1997), Fang et al (2008), Jiang et al (2011), and Ashnai (2014) have also researched and explored multi-level trust, providing evidence for discriminant validity between inter-organisational and interpersonal aspects of trust. This thesis establishes the third level of inter-team/operations.
Managers need to be clear about the relational intentions they set in terms of customer or supplier expectations and the organisation’s ability to meet them. Managers need to ensure relationship measures reflect the true role of commitment in trust development. This has implications for the use of net promoter score (NPS) in B2B relational contexts.
At the initial stage of the relationship, the intention enacted has the potential to create dissonance if the intention enacted falls short of the expectations established at the intangible stage. The intention shortfall could be on a cognitive or affective level or a combination of both (Dowell, 2015; Akrout, 2017). This thesis established the potential for dissonance occurring at the team/operations and interpersonal level between the dyad, as one side of the dyad failed to live up to the intentions established at organisational strategic level.
Through the use of multi-level research across both sides of the relationship dyad and multiple research partners, this thesis addresses gaps in B2B trust research methodology. It also contributes an understanding of how trust can be proactively developed (intention, ability, credibility, interdependence, mutual value benefit), the roles of cognitive and affective trust, and where these reside at organisation, group/team and interpersonal levels.
Therefore, this thesis extends our understanding of different aspects of trust by applying a research methodology that negates misspecification, making a methodological contribution to B2B research through the use of three methods in triangulation. Furthermore, the qualitative research approach is enhanced through the introduction of a bridging process between first- and second-cycle coding, independently validating, informing and contributing to theory development. This adds to the limited number of studies that have attempted to do so (Zaheer et al, 1998; Currell and Inkpen, 2002; Fang, 2008; Ashnai, 2014; Dowell, 2015; Nikolova, 2015; Stevens et al, 2015; Saunders, 2016; Akrout, 2017).
This thesis makes a practical contribution to the body of literature and theory in B2B trust between two organisations in a relational context in the following areas:
- It differentiates from previous studies investigating the importance of commitment in the development of trust in B2B organisational relationships (Morgan and Hunt, 1994; Mouzaz et al, 2007; Ashnai 2014). As this thesis contributes to an understanding through highlighting the importance of relationship intentions, as opposed to commitment at an organisational level, it builds on intentionality in the trust-building process (Doney & Cannon 1997) as the strategic mediating effect cross dyad through the relationship intentions both sides have towards the relationship. Therefore, managers need to be clear about the relational intentions they set in terms of customer or supplier expectations and the organisation’s ability to meet them. Managers need to ensure relationship measures reflect the true role of commitment in trust development. This has implications on the use of net promoter score (NPS) and how customer relationship quality (CRQ) is established in a B2B relational context. Additionally, the thesis highlights both commitment and communication as important linking antecedents of B2B relational trust at operations/team and interpersonal level, as intention moves from intangible to tangible action between both sides of the relationship. This offers managers the potential to track and measure implementation at these levels through the commitment and communication being undertaken between the dyad and within the organisations and the delivery of the relational intent.
- Social exchange theory assumes that the role of social interactions and interpersonal relationships are critical in exchanges such as business relationships, (Blau 1964; Emerson 1981). Both social and structural characteristics are considered as influential factors when examining business relationships, (Wilson 1995; Blois 1999; Ashnai 2014). This thesis confirms the proposition made by social exchange theory that emotions and feelings play a role in business relationships, which involve social exchanges (Thibaut and Kelley 1959; Ashnai 2014) as was evidenced in the role of affective trust expansionist/reductionist antecedents between both sides of the relational dyad. Relationship consonance occurring through cognitive, affective antecedents and/or combination has an expansionist effect on trust development. In this context, managers/leaders need to match resources for the optimum effect in the early relationship effective stage. Care needs to be taken that the relationship doesn’t get stuck at this stage and smoothly transitions into the cognitive stage. Careful selection of the boundary spanners and commensurate development is required in order to effectively manage this transition. The resource-based view, highlights implementation strategies that enable firms to gain competitive advantages, accessing and managing resources productively, and profitably (Wernerflet 1984; Barney 1986; Ashnai 2014). This thesis contributes to this perspective by developing the theory of dissonance and consonance that incorporates two different groups of characteristics, affective/emotional and cognitive/rational, which have a reductionist and/or expansionist effect on B2B relational trust development between both sides of a relational dyad, operating as a supporting link. It is therefore vital that managers/leaders regularly and objectively survey both sides of the relational dyad. Doing so, would determine the affective/cognitive balance and nature of trust development, enabling corrective action to be taken if required.
- The relationship boundary spanners have a mitigating effect on the movement from relational intent (intangible) to relational action (tangible), reducing vulnerability and leap of faith, which supports the earlier work of Naslund (2012 p.23), suggesting that: “interpretation and expectation are largely based on cognition, while the leap of faith relies more on the affective aspects”. The thesis uncovered the role of the boundary spanners and affective trust as having a positive impact on the move from intangible trust as organisational intention towards the activation and into tangible trust. An additional role of relationship trust developer needs to be considered for the boundary spanners and closely related relationship stakeholders, as they take on the responsibility for risk mitigation through relationship trust development. This would require systematic development of capability and competency in this relationship development for the boundary spanners and connected stakeholders – in essence, holding the hand of one side of the relational dyad as they make the step (rather than the leap of faith) (Mollering 2002) to mitigate the risk and ameliorate the vulnerability.
- The thesis identified trust residing at organisational level manifested through moral bonds (cultural), action and behavioural conceptualisation. Trust has been argued to pass into the collective entity over time, (Clark 2010) and is seen to live in a state beyond the collective individuals, confirming and supporting (Fleetwood 2018) conceptual structuration theory. It also posits an answer to the academic conundrum of where does trust reside in an organisation, which in turn contributes to social exchange theory (Szomptka P 2016), and supports the conceptualisation of an organisation’s actions as a characteristic of trust (Stevens et al 2015). It also confirms the strategic importance of the leadership team (Legood et al 2016) in shaping organisational trust through the development and signalling of relationship intentions. The implications are significant for leaders as they have responsibility not only for the strategic intent, but also the development of the organisation’s moral bonds. These emanate from the organisational leadership’s actions and behaviours, passing into organisational culture over time. At an operations, team and interpersonal level, the contribution builds on structuration theory. The implications for leaders in the creation of organisational trust is ensuring the relational intent manifests in the artefacts at operations/interpersonal level, this is communicated effectively, and then checked for understanding, relevance and appropriateness at inter-operations and interpersonal levels: ways of working, actions and behaviours are briefed effectively, trained, embedded and rewarded; undertaken until they become organisational muscle memory, overwriting the historic ways of working. This thesis demonstrates trust residing at these levels as a manifestation of artefacts (relationship charter/mission/vision) standard norms (contracts, processes, systems and ways of working) and cognitive social stuff as the effective memories of the relationship agents.
- The practical contribution to theory and literature of B2B customer management, marketing, partnerships, sales and purchasing is made by introducing a model of B2B relationship trust building. The model (see Figure 3) contributes by developing an: intention-ability-credibility-interdependence-mutual value outcomes–time framework that works across all organisational levels and between dyads. In essence, this provides managers/leaders with a B2B relational trust development blueprint, the “how to guide”. This starts and emanates from organisational level as strategic intent, turned into relationship reality at operations level and then into the effect seen through the creation of mutual value. It builds on the definition of B2B trust, and sheds light on how both sides of the relationship can work proactively to use trust to develop the relationship. It provides a sense check as the framework, if applied from an opportunistic/coercive behavioural perspective, has the potential to develop dissonance and a reductionist effect on the relationship. The application of the trust DNA model has a positive impact on trust development in a B2B relationship and can be proactively planned and applied. Additionally, the thesis bridges two perspectives into the study of business relationships (ie, social exchange theory and resource-based view), as they both play a role in shaping this model/framework, particularly due to the emphasis on outcome(s) from the relationship in the form of mutual value outcomes and the role of ability and credibility antecedent resource allocation to achieve them. The application of the trust DNA model and its reductionist/expansionist potential impact on the relationship contribute to the understanding of trust as being dynamic in nature through constant updating and/or recalibration of trust between both sides (Stevens et al 2017).
The research was conducted with organisations all of which operated the relationship researched in the United Kingdom. This means the findings of this thesis may not have validity in other regions or geographies. The regional variations in terms of business ethics and business culture would need to be considered.
The organisations researched all operate across a number of distribution channels, with the internet and online business being a key element. However, the online channel was not explicitly researched and therefore may need further consideration and/or exploration.
This thesis and research explored B2B trust across dyads and at three different organisational levels: inter-organisational, inter-team/operations and interpersonal. In total, 37 people were interviewed. When matching respondents to organisational level, the research cohort at staff/interpersonal level would have benefited from additional respondents to balance with the organisational and inter-team/operations/managerial level.
The qualitative research reached saturation before the total number of respondents (37) were interviewed; however, it could have benefited from more respondents from the fast-moving goods and financial sectors research partners. When broken down between the supplier/customer sides of the dyad, the number of respondents became somewhat diluted, and could have benefited from additional respondents from both sides.
The research focused on the private sector and one quasi-private/public sector organisation and thus may be subject to issues of generalisability beyond the sectors researched, ie the third sector, industrials/auto/manufacturing).This thesis is predicated on the research gathered from organisations representing the fast-moving consumer goods, grocery retail, healthcare distribution and retailing, pharmaceutical, utilities and outsourced services sectors. As such, it may not reflect the relational and trust dynamics in the third sector, public sector and other business sectors not covered in this thesis.
Areas for further research
Other regions – Scholars focusing on researching B2B trust using a cross dyad by organisational-level methodology would benefit from building on this thesis to explore additional areas for further research, extending the research to encompass other regions could offer a comparative analysis on the differences among other regions when researching B2B relational trust. Exploring a specific market or country may also add richness to the current research and build on the findings.
Third sector – The development of the research into the third sector would provide an interesting build on the findings. It could also allow comparative analysis by level and cross dyad. The public sector also holds significant opportunity as significant relationships exist between the public sector and business. Research into this sector could provide further insight into mutual value benefit from a not-for-profit relational perspective.
Zero-sum game – An interesting area for potential further research exploration, which surfaced during the initial research phase, is the use of trust in a zero-sum game scenario. This could in some way be linked to calculative trust (Williamson, 1975; Lewicki and Bunker, 1985); however, it actually appears to go beyond this as it relates to relationships where failure is too great to contemplate. In this instance, the trust is based on an unknown or known fear of what the consequences could be if one side cannot trust the other.
Unfortunately, we do not have space for the extensive list of references supplied. Please contact the author for further information about the literature.