Zane is interested in the proportion of people who recycle each of three distinct products: paper, plastic, and electronics. He wants to test the hypothesis that the proportion of people recycling each type of product differs by age group: 12–18 years old, 19–30 years old, 31–40 years old, and over 40 years old. Describe the sampling method appropriate for a test of homogeneity regarding recycled products and age.