Answer:
The coefficient of imitation.
Step-by-step explanation:
The more people talking about a product, the more other people in the same social system will adopt the product. This is also called "parameter of internal influence". This, as the exercise details, measures the likelihood od adoption due to a potential adopter being influenced by someone who has already adopted the product.
The coefficient of imitation Q received it's name because it's effect is proportional to cumulative adoptions, implying that the number of adoptions at a certain time is proportional to the number of prior adopters.