Gap theory, or the Service Quality Gap model was proposed by Parasuraman, Zeithaml, and Berry in 1985.
This models identifies the different sources of gaps or differences between the service quality that a customer expect to receive from a service provider and the customer perception of of the service actually received.
The model identifies 5 different types of gaps. The first four gaps are called company gaps, and the last or fifth gap is called customer gap - that is, the gap as perceived by customer. The customer gap is the resultant effect of the four company gaps. The description of these five quality gaps is given below.
Gap 1:The difference between the the service actually desired by the customer and company's perception of what the customer desires.
Gap 2: The difference between company's understanding of the service desired by customer and the service as designed to be delivered by the company, and the performance standards set for the same.
Gap 3:The difference between the service design and actual service delivered.
Gap 4: The difference between actual service delivered and the service as perceived by customer.
Gap 5: The difference between service as perceived by customer and service expected by company.
Parasuraman A., Zeithaml V.A. and Berry L.L. "A Conceptual Model of Service Quality and Its Implications for Future Research". Journal of Marketing. Vol. 49, Autumn 1985.