Read the study by Bob E. Hayes, Ph.D. in the June 2008 edition of Quality Progress magazine titled The True Test of Loyalty. This Quality Progress article discusses the measurement of customer loyalty. Despite its importance in increasing profitability, customer loyalty measurement hasnât kept pace with its technology. Using advocacy, purchasing and retention indexes to manage loyalty is statistically superior to using any single question alone. These indexes helped predict the growth potential of wireless service providers and PC manufacturers. You can download the article here.