IT IS hard to be an optimist about the housing market these days, but those so inclined like to note that as long as the population keeps growing, so should the demand for homes. But what if the larger population decides to share the same number of homes?

America's census bureau has been publishing massive amounts of data from several, parallel surveys of the population in recent weeks. One of its more intriguing findings is that after shrinking for decades, households have started to grow. Last year the average household had 2.59 people, up from 2.56 two years earlier, marking the first increase since 1993.

This is not because parents are having more children. According to Julia Coronado and Yelena Shulyatyeva of BNP Paribas, a bank, it is because the children they have are taking longer to move out. They calculate that the proportion of adults aged 25 to 34 still living with their parents has risen to 13.4%, from 12.7% in 2008.

There are other signs that Americans are more inclined to stay put these days. The proportion of people who changed homes last year fell to 14.9% from 15.4% in 2007, due no doubt both to the lack of employment opportunities and the inability to sell a home that is worth less than its mortgage. People are delaying marriage: the proportion of people who have never been married rose sharply, to 28.6% of women and 35.2% of men. They are also having fewer children.

Much of this is almost certainly a response to the recession and the surge in unemployment. For young people who have lost their job or cannot find their first one, living with their parents becomes more attractive. Census data have corroborated the devastating impact on households. Median income fell 0.7% after inflation, in 2009, finishing the decade down a shocking 5%; the poverty rate rose to 14.3%, the highest since 1994, from 13.2% and the proportion of the population lacking health insurance also rose, to 16.7%.

As the economy recovers, some of those people will move out of their shared homes and buy their own. But the reversal could be a way off, and slight. Ms Coronado notes that household size shrank over recent decades first as birth rates declined, then as baby boomers' children moved out. The latter is almost a spent force. Another factor that had driven down household sizes in the last decade was the proliferation of mortgages allowing people to buy their first home with little or no money down. That was unsustainable.

If households are slow to shrink back, it has sobering implications for many industries. It will slow the process of reoccupying vacant homes and bringing construction back to life. Larger households means more people sharing televisions, refrigerators and cars, and so fewer sales of new ones. The share of households with two or more cars dropped to 57.5% from 58.2% in 2007. When young people do move out, they are more likely to rent than buy. The proportion of households who rent has risen sharply since 2007, as has the number of people in each rental household.

At least the homes themselves are not getting any smaller. The typical home has more bedrooms than it did two years ago. But, as Ms Coronado speculates, “The cleanliness of the bathroom has probably deteriorated.”