To monitor customer satisfaction and to take action to improve it, a number of different methods have been developed. The Customer Satisfaction Index (CSI) is one such method. The American Customer Satisfaction Index (ACSI), developed by the University of Michigan in 1994, is a scientific standard of customer satisfaction. Among APO member countries, the Republic of Korea and Singapore use ACSI methods. Research has shown that the national CSI score is a strong predictor of GDP growth, and an even stronger predictor of personal consumption expenditure growth. At the microeconomic level, CSI data predict stock market performance, both for market indices and for individually traded companies. A high CSI is correlated with higher financial returns and strong customer loyalty. A CSI also allows companies to understand their market positions and help identify areas for productivity improvement.