Incentives for Creating Or Joining an Interest Group

Solidary Incentives - Reasons or motives having to do with the desire to associate with others and to share with others a particular interest or hobby. These incentives include companianship, a sense of belonging, and the pleasure of associating with others. Link - Pewter Report

Material Incentives - Reasons or motives having to do with economic benefits or opportunities. Link - National Farmers' Union (NFU)

Purposive Incentives - Reasons or motives having to do with ethical beliefs or ideological principles. Interest groups offer the opportunity for individuals to pursue political, economic, or social goals through joint action. Purposive incentives offer individuals the satisfaction of taking action for the sake of their beliefs or principles.
Link - National Right to Life