The population of Paris today is lower than its historical peak of 2.9 million in 1921. The principal reasons were a significant decline in household size, and a dramatic migration of residents to the suburbs between 1962 and 1975. Factors in the migration included de-industrialisation, high rent, the gentrification of many inner quarters, the transformation of living space into offices, and greater affluence among working families. The city's population loss came to an end in the 21st century; the population estimate of July 2004 showed a population increase for the first time since 1954, and the population reached 2,234,000 by 2009.