businesses density, businesses size, industrial mix, neighborhood income, and the credit quality of local businesses. Gregory D. Squires wrote in 2003 that it is clear that race has long affected and continues to affect the policies and practices of the insurance industry. Workers living in American inner cities have a harder time finding jobs than suburban workers. The desire of many whites to avoid having their children attend integrated schools has been a factor in white flight to the suburbs. A 2007 study in San Francisco showed that groups of homeowners of all races tended to self-segregate in order to be with people of the same education level and race. By 1990, the legal barriers enforcing segregation had been mostly replaced by decentralized racism, where white people pay more than black people to live in predominantly white areas. Today, many whites are willing to pay a premium to live in a predominantly white neighborhood. Equivalent housing in white areas commands a higher rent. These higher rents are largely attributable to exclusionary zoning policies that restrict the supply of housing. Regulations ensure that all housing units are expensive enough to prevent access by undesirable groups. By bidding up the price of housing, many white neighborhoods effectively shut out black people, because they may be unwilling, or unable, to pay the premium to buy entry into these expensive neighborhoods. Conversely, equivalent housing in black neighborhoods is far more affordable to those who are unable or unwilling to pay a premium to live in white neighborhoods. Through the 1990s, residential segregation remained at its extreme and has been called "hypersegregation" by some sociologists or "American Apartheid". In February 2005, the U.S. Supreme Court ruled in Johnson v. California that the California Department of Corrections' unwritten practice of racially segregating prisoners in its prison reception centers—which California claimed was for inmate safety (gangs in California, as throughout the U.S., usually organize on racial lines)—is to be subject to strict scrutiny, the highest level of constitutional review. Yemen In Yemen, the Arab elite practices a form of discrimination against the lower class Al-Akhdam people based on their racial characteristics. See also Afrophobia Amity-enmity complex Black Lives Matter Black nationalism Black power Black power movement Black separatism Black supremacy Caste Discrimination Discrimination based on skin color Ethnic nationalism Ethnocentrism In-group and out-group Nationalism Nativism (politics) Racial discrimination Racial hierarchy Racial nationalism Racism Supremacism White nationalism Xenophobia