Service Gap Model
The service gap model is based on the model as described in the book Delivering Quality Service by Valerie Zeithaml, et.al ISBN 0 02 935701- 2
I use this service gap model on a regular basis, but always with the reference. Although the model is slightly adapted I think it is close enough to attribute to the authors of Delivering Quality Service Book.
If I missed the reference in the book - I apologize