It now takes more than a year of work for the average American to earn enough income to pay for a year at a private college, where costs have risen more rapidly than inflation for 26 consecutive years.

But by one measure, American colleges cost less than they used to. Those who plan on paying for their children's education by selling part of their stock portfolios now need to sell less than half as many shares as their parents would have had to sell a quarter century ago.

The College Board, a research organization, this past week released its latest study of average college costs. For the current school year, the average for a private four-year college is $30,367, while the average cost for a public college in the United States is $12,796.

Both figures were up almost 6 percent from the previous year and outstripped gains in the overall rate of inflation.

Those figures include tuition, room and board, but exclude the cost of books, which has been rising rapidly. And they are averages that significantly understate the cost of top universities, where total costs are over $40,000 an academic year.

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The accompanying charts show the annual costs for the past 30 years in three ways.

First, the figures show the costs for public and private colleges in 2006 dollars, thereby adjusting for inflation.

The second chart shows the annual cost of public and private colleges as a multiple of the average pretax weekly earnings of workers in American industry, as reported by the U.S. Labor Department.

Thirty years ago, private college costs were equal to 21 weeks of average pay. Now the figure is 53, or more than the average worker earns in a year.

The public college cost, expressed that way, has more than doubled from 10 weeks to 21 weeks.

Sandy Baum, a senior policy analyst at the College Board and a professor of economics at Skidmore College, said she hates to see such figures published.

"What worries me is that people throw up their hands and say, 'I cannot pay that,'" she said.

She added that people with average- level incomes usually could get aid to enable their children to attend college for far less than the posted prices.

At private colleges, College Board figures show the average student now pays about 70 percent of the posted price, down from 73 percent in the late 1990s.

The third chart shows the cost of college relative to stock prices.

It is expressed in units of the Standard & Poor's index of 500 stocks, and based on the closing price each September. Back in 1982, the S&P was at 120, and you would have needed 59 baskets of S&P stocks to buy a year at the average private college.

Now, with the S&P above 1,300, such a year costs just 23 baskets of stocks.

For the wealthy with lots of financial assets, college costs less than it used to. For those who depend on their jobs for income, the opposite is true.

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