3Aaker, David A., V, Kumar, and George S.Day(1998), Marketing Research, New York: John Wiley &.Sons.
4Reichheld. Frederick F. & Thomas Tcal (1996), The Loyalty Effect, Harvard Business School Press.
5Wemer J, Reinartz & V, Kumar (2000) , On the Profitability of Long Life Customers in a Noncomractual Setting: An Empirical Investigation and Implications for Marketing,Journal of Marketing(October).
