User involvement and participation can make a big difference especially in IS project productivity. We all "know and believe this "but in the LABINAL case we have a good and convincing example. In the two projects: pilot project and main project, all factors have been kept equal, only one factor changed: the user participation and involvement. The difference in productivity is striking, pilot project: 92.4 function points per person*month and main project: 48.4 function points per person*month.
BRIOLAT, D. and POGMAN, J. (1999). Use of Function Points in a Quasi Experiment about User Participation Influence on Project Productivity in a RAD Environment.