What is the fine-grained topic of the following text: "[Nearly] 3,000 persons randomly selected from the church member population of four Northern California counties...completed a lengthy and detailed questionnaire....This sample was obtained first by randomly selecting a sample of congregations, weighted for size, from all Protestant and Roman Catholic congregations in the four counties...a random sample of members was obtained by sampling individual membership lists." Only return the topic.
Survey methodology in religious population research