An important concern in immigration research involves the effects of immigration and assimilation on health, education, and social programs, particularly in areas of high immigration concentration. Much folk wisdom has viewed assimilation as a linear process of progressive improvement and adjustment to American society. The general assumption is guided by an implicit deficit model: to advance socially and economically in the United States, immigrants need to "become American" in order to overcome their deficits in the new language and culture. As they shed the old and acquire the new, they acquire skills for working positively and effectively—a process that may not be completed until the second or third generation after entry.