Full context:   To overcome the deficiencies of the 4P model, some authors have suggested extensions or modifications to the original model. Extensions of the four P's are often included in cases such as services marketing where unique characteristics (i.e. intangibility, perishability, heterogeneity and the inseparability of production and consumption) warrant additional consideration factors. Other extensions include "people", "process", and "physical evidence" and are often applied in the case of services marketing. Other extensions have been found necessary in retail marketing, industrial marketing and internet marketing.