"relationship revenue". A useful calculation for this is the patronage concentration ratio. This calculation is hindered by the difficulty in allocating costs to individual relationships and the ambiguity regarding relationship cost drivers. Expanded models Virtuous Circle Schlesinger and Heskett (1991) added employee loyalty to the basic customer loyalty model. They developed the concepts of "cycle of success" and "cycle of failure". In the cycle of success, an investment in your employees’ ability to provide superior service to customers can be seen as a "virtuous circle". Effort spent in selecting and training employees and creating a corporate culture in which they are empowered can lead to increased employee satisfaction and employee competence. This will likely result in superior service delivery and customer satisfaction. This in turn can create customer loyalty, improved sales levels, and higher profit margins. Some of these profits can be reinvested in employee development thereby initiating another iteration of a virtuous cycle. Fred Reichheld (1996) expanded the loyalty business model beyond customers and employees. He looked at the benefits of obtaining the loyalty of suppliers, employees, bankers, customers, distributors, shareholders, and the board of directors. Duff and Einig (2015) expanded the model to debt issuers and credit ratings agencies to investigate what role commitment plays in issuer-CRA relations. Satisfaction-profit-chain (SPC) model The satisfaction-profit chain is a model that theoretically develops linkages and then enables researchers to test them statistically for a firm using customer data (both from surveys and other sources). The satisfaction-profit-chain was tested in the context of banking industry showing that product and services improvements indeed were associated with customer perceptions, which led to beneficial customer behaviors such as repurchase, and desirable financial outcomes such as increased sales and profitability The satisfaction-profit-chain, as a methodology for managing customer loyalty and firm profitability, is also applicable in business-to-business markets, irrespective of whether the B2B firm sells goods and/or services. The satisfaction-profit-chain refers to a chain of effects whereby increased performance on key attributes leads to improvements in overall satisfaction, which in turn affects loyalty intentions and behaviors. The increased customer loyalty is shown to affect short- and long-term financial outcomes including sales, profitability, and stock price. More recently, some studies show that especially in the context of services such as retailing and financial services, employee satisfaction can play a critical role in enhancing customer loyalty. This happens because both customer satisfaction and employee satisfaction can mutually reinforce