Parents who send their children to four-year colleges have long been above average when it comes to income. But today's freshmen are financially better off than ever before, and the gap is widening, a report on 40-year trends in higher education shows.

Freshmen in 2005 reported median family incomes 60 percent higher than the national average, says the report, released Monday by UCLA's Cooperative Institutional Research Program. In 1971, incomes were 46 percent above the national average.

"Not only (does) the gap exist, it's growing," says report co-author Jose Luis Santos, a UCLA assistant professor of education.

The findings are based on data collected since 1966 as part of the UCLA program's annual report on freshman attitudes, characteristics and behaviors. More than 8.3 million first-year students at 1,201 four-year colleges and universities nationwide have participated.

A number of studies in recent years show that highly selective private colleges and public flagship universities are enrolling disproportion- ately fewer students who qualify for need-based aid. The UCLA survey, which asks students to estimate their parents' income, offers greater specificity.

"It gives a hard number that says, 'This is how much (incomes diverge),"' says Bryan Cook of the Center for Policy Analysis at the non-profit American Council on Education, an umbrella group for colleges and universities.

Students who attend four-year private universities report higher median incomes than those at four-year public universities, but the gap is closing. Median parental incomes for students at private universities increased 15.7 percent, to $83,500 in inflation-adjusted dollars, from 1971 to 2006. For students at public universities, the incomes rose 17.1 percent, to $73,400, in inflation-adjusted dollars.

UCLA's analysis pinpoints the mid-1980s as a watershed period: From 1983 to 1987, student-reported median family incomes shot up 21 percent to $76,100, while the national average increased 9 percent, to $46,200, in inflation-adjusted dollars.

Around the same time, real wages began to lose value for many families, particularly those with blue-collar manufacturing jobs, Santos says. That's also when public and private university tuitions first began ratcheting upward.

The study did not examine community colleges or for-profit schools, where low-income students are more likely to begin their postsecondary education.

But with four-year degrees, the "aspiring standard" in higher education, Santos says, the findings provide insight into the growing divide in the more elite institutions.