A class system is a form of social ranking based primarily on economic position in which achieved characteristics can influence mobility. Unlike caste systems, where social position is ascribed at birth and cannot be changed, class systems allow for social mobility, the movement of individuals or groups up or down the social hierarchy, based on factors such as education, occupation, and income (achieved characteristics). While economic factors are central to class systems, social status and power also play a role. Class systems are characteristic of modern industrial societies and are considered more open than caste systems, although the extent of social mobility can vary significantly. Sociologists often study class systems to understand patterns of inequality and the factors that influence social mobility.