Family sociology is a subfield of sociology, and researchers see the family as one of several key social institutions and socialized units. Family sociology is a common part of the introductory and pre-university courses, as the topic provides a familiar, illustrative, exemplary social relationship and dynamic paradigm. To consider the sociology of the family, sociologists use family culture as the largest research tool. They do this by examining the existing structure and practices of each household to understand the components of the larger unit. The sociology of the family is based on many cultural factors that influence its structure and processes, and sociologists must study these factors to understand the many complexities of the field. Factors such as gender, age, race and ethnicity are just some of the factors that affect relationships, structure and customs within each family. Changing demographics also often affect family culture, and sociologists seek to understand why and how.