How much is a premium college degree really worth?

If college is an investment in your future, how can you be sure you'll be getting the best return on the money and time spent earning a degree?

With the rising cost of college tuition, it's a serious question that many high school students and their families are now facing. After all, the class of 2015 walked out of their graduation ceremonies as the most indebted college graduates ever, with an average student-loan debt of more than $35,000.

Now, the U.S. Department of Education is sharing data that may help students understand how much their degrees may be worth after graduation -- and whether a college offers enough of a salary boost to justify its tuition. It's no surprise that the colleges that offer the best value -- the lowest net cost for low-income students combined with high median earnings a decade after graduation -- are some of the top-ranking U.S. schools: Harvard, Princeton, and Stanford are among them.

Yet there's some eye-opening information within the new site's mountain of data. For one, many colleges with good reputations may not be providing a healthy return on investment for their graduates, based on data provided by the Department of Education's College Scorecard. Still, experts caution that families should interpret the data with some caution, given that it's based on data from students who received federal aid, which limits the data pool.

"If you have to take a lot of debt, you have to understand your ability to pay it back after graduation," said Lydia Frank, senior director at Payscale, a compensation research firm. "We're asking 18-year-old kids to think pretty far ahead when historically we've told them, 'Just follow your heart,' which is great advice if you have endless amounts of money to spend on your education."

Take Bard College, a well-regarded liberal arts institution in Annandale-on-Hudson, New York. It's ranked 45th on U.S. News & World Report's list of top national liberal arts colleges.

The school has an above-average annual cost, at $27,556, although graduates are earning on average only $34,343 a year a decade after they received their degrees, or at about the national average, the College Scorecard notes. On the other hand, only 47 percent of Bard graduates are earning more than Americans with only a high school degree.

The federal government's data is flawed, given that it only represents those who have taken out federal loans and doesn't account for other issues, such as majors and socio-economic status, said Bard spokesman Mark Primoff.

"I find it unfortunate that, acting under the pretense of trying to inform students and parents, the Federal Government has resorted to compiling and distributing raw, nearly random data without explaining its flaws," he wrote in an email. "For example, by only taking small segments of each school's graduates (those who have taken Federal loans, which differ from school to school), the figures they cite are inherently suspect. Add to that the other factors that are not accounted for: the socio-economic status of those entering school, the majors chosen and the academic success of each student, the fields they choose to enter, and you end up with something that looks like data but is fundamentally meaningless."

There are many other colleges with similar profiles: Above-average costs and a relatively high percentage of graduates earning salaries similar to high school grads. While striving for a college education isn't only about maximizing earnings potential -- college grads are more satisfied with their jobs and are more likely to be employed than the less educated -- the data may raise questions from families about the wisdom of taking on a pricey college degree versus enrolling at a less expensive institution with similar salary outcomes.

Students enrolling in expensive private colleges can find financial aid, of course. But even that might not be enough to defray the costs and provide a better financial outcome. Families earning $48,001 to $75,000, or solidly middle class but by no means wealthy, will pay an average cost of $25,999 for their student to attend Bard annually, the Department of Education notes. That's a hefty chunk of that family's income, which means that those students will likely turn to loans to secure their education. The typical total debt load for Bard graduates is $24,000, according to the scoreboard.

The data illustrates that aside from wealthy universities such as Harvard, which offer both generous financial aid and the cachet to help boost salaries, some pricey, well-regarded private colleges may not provide a healthy return on investment. Families may want to consider their state's public university system as an alternative, given their generally lower tuition.

The University of Illinois at Urbana-Champaign, which is ranked No. 41 on the U.S. News & World Report's list of national universities, has an average annual cost of $18,798, according to the Education Department. Even better, the average salary for grads a decade later was $56,600, or well above the national average. More than three-quarters of its grads are earning more than Americans with only high school degrees.

To be sure, the College Scorecard is missing some nuance. The main problem is how the scorecard doesn't separate out how graduates perform according to their major. Universities that specialize in STEM-focused fields such as engineering -- MIT and Harvey Mudd Collge, among them -- tend to graduate students with salaries that are well above the national average. In a separate study published last month, Payscale found that the colleges with the highest-paid graduates tend to be those focusing on the STEM fields.

With Bard College, however, there's no way to tell how its STEM-focused grads perform compared with those in the humanities, where salaries tend to be lower.

That shortfall was called out by the American Council on Education, whose president warned that the College Scoreboard may not provide complete information to families.

"Given what we believe are significant data limitations, this revamped Scorecard may or may not provide meaningful information to the students and families it was designed to help," said ACE president Molly Corbett Broad in a statement. "For example, it appears the system only provides a single number for an entire institution regardless of whether a student studied chemical engineering or philosophy, and only includes the earnings of federal financial aid recipients."

Editor's note: This story has been updated to include comments from Payscale and Bard College.