Final answer:
Group practice growth is fueled by purposive, solidary, and material incentives, which drive individuals to join and contribute to groups with shared goals, enjoyment of fellowship, and tangible benefits, respectively.
Step-by-step explanation:
The growth of group practice can be linked to incentives that facilitate and encourage individuals to join and remain within a group. Three types of incentives include purposive incentives, solidary incentives, and material incentives. Purposive incentives drive people to contribute to a group in order to support shared goals, such as how ACLU membership increased after 9/11 due to shared civil liberty concerns.
Solidary incentives appeal to the enjoyment of association with like-minded individuals, for example, members joining the Union of Concerned Scientists. Material incentives offer tangible benefits, such as AARP providing health insurance and discounts, attracting a broad membership base. Moreover, effective leadership within groups can offer these various incentives to resolve collective action problems and stimulate long-term growth.