We estimate that a relatively low level of disparity in replacement rates will result in smaller market-share shifts in the future.

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For many employees covered by them, net replacement rates will be adequate.

ECONOMIST: Ageing and public finances

There were also increases in labour-market flexibility through improving job search for those on benefits, reducing replacement rates, increasing in-work benefits and restricting union power.

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The obligation to retirees is skyrocketing due to lengthening lifespan, and the number of workers contributing into such funds is declining due to below-replacement fertility rates.

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The odd ones out are America and Britain, which both have lots of women at work and fertility rates close to replacement level (with immigration making up the rest).

ECONOMIST: Most of the rich world is short of babies

Western European countries have low fertility rates, below the replacement rate of 2.1.

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In Europe, birth rates are below the replacement level.

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Current rates, he says, are below replacement levels and are unsustainable.

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Extensive research in 16 OECD countries has shown that there is a strong correlation between high female employment rates and large government cash transfers to families, generous replacement pay during parental leave, the availability of plenty of part-time work and lots of formal child care.

ECONOMIST: Most of the rich world is short of babies