Strauss and Gove define a generation as the set of all people born in a time span of approximately 20 years, or one phase of life: childhood, youth, middle age, and old age. A generation can be identified if it meets three criteria. First, members of the same generation share the same historical era: they face the same key historical events and social trends, being in the same life stages. Second, they share certain common beliefs and behavioral patterns. Third, knowing the experiences and characteristics they share with their peers, members of the same generation will also share a sense of belonging to that generation.