Only a quarter of migrant workers in the cities were covered by pensions in 2010, compared with four-fifths of locals, according to Albert Park of the Hong Kong University of Science and Technology.

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The stimulus package got most of them back to work quickly, but a lot of those migrant workers stayed in the interior cities because wages had improved along with working conditions.

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Migrant workers often can't register in the cities where they work, and subsequently can't qualify for social services such as public education or social security.

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