The final link in the model is the effect of customer loyalty on profitability. The fundamental assumption of all the loyalty models is that keeping existing customers is less expensive than acquiring new ones. It is claimed by Reichheld and Sasser (1990) that a 5% improvement in customer retention can cause an increase in profitability between 25% and 85% (in terms of net present value) depending upon the industry. However, Carrol and Reichheld (1992) dispute these calculations, claiming that they result from faulty cross-sectional analysis.