Last November, in a message to alumni, Oklahoma State University president Burns Hargis said, “College graduates strengthen a state’s economy, lift up communities, and earn about twice as much over a lifetime as high school graduates. I often say that a college degree is a passport to prosperity and a hedge against poverty. It’s true!”

That is the conventional wisdom about college. Those who get their degrees are almost certain to enjoy a big payoff—much higher earnings, less likelihood of unemployment—and the more college grads a state has, the better off it will be.

Hargis has lots of company in his view that college is a great investment. Recently, Justin Wolfers, a professor of business and public policy at the famous Wharton School, looked at some Bureau of Labor Statistics (BLS) data (pictured below) that appear to show strong benefits from getting more education. He then posted on Twitter: “Hey kids, stay in school. What would happen if we put this poster in every classroom?”

At a glance, you can see how the chart seems to prove Hargis and Wolfers right. Looking at the chart, it seems obvious that the path to financial success is to get a college degree—and then an advanced degree. The more education you have, the better off you’ll be. High-school graduates, for example, are almost twice as likely to be unemployed as college graduates, and they earn substantially less money per week.

Before students in Oklahoma (or any other state) jump to the conclusion that college is an almost sure thing—an investment that can’t miss—they ought to take a more careful look. The data are misleading.

First, all of these statistics are the median—representing the person separating the higher half of a sample from the lower half. It’s a mistake to assume that the median tells us what most people in that group will experience.

Thinking of the median as “typical” masks a lot of important details about educational outcomes.

To start with, note that the data are 2010 median weekly earnings for persons age 25 and over, and earnings are for full-time wage and salary workers. So, everyone is lumped together—regardless of age, the school they attended, their major discipline, their academic performance, and even the field in which they’re working. And anyone working part-time is excluded entirely.

Breaking the data down further is illustrative. Among workers making $20,000 or less annually, 6 percent have master’s degrees or higher, 14 percent have bachelor’s degrees, and 9 percent have associate’s degrees. Among those making between $20,000 and $35,000 annually, 5 percent have a master’s or higher, 15 percent have a bachelor’s, and 11 percent have an associate’s degree.

Those individuals are earning well below the medians for their educational levels. Staying in school didn’t necessarily pay off for them.

The chart also hides an important phenomenon that has become increasingly common in the last few years—unemployment and underemployment among people who have college credentials. As a recent Gallup poll indicates, as of July 2010 almost 14 percent of those surveyed who had B.A. degrees, and over 10 percent of those with postgraduate degrees, were unemployed or underemployed.

Another reason why the BLS chart is misleading is that it lumps together people of all ages, who are at different levels. People with professional degrees, for example, include many lawyers who earned their degrees years ago, many of whom have high earnings (the median is $1,610 per week, or over $83,000 annually). That information is of no relevance to a brand new J.D., who faces a job market that has shrunken greatly in the last few years. Many recent J.D.s are scrambling to find any job at all.

Furthermore, returns to higher education have been declining for more than 10 years, according to the U.S. Census Bureau. Median starting salary for bachelor’s degree recipients in 2009 and 2010 was just $27,000, down from $30,000 in the years 2006 to 2008. The chart gives us a snapshot in time, but trends also matter, and the trend is downward for college degrees.

Earnings also vary greatly depending on the student’s major. Data from the U.S. Census Bureau show that median earnings run from $29,000 for counseling-psychology majors to $120,000 for petroleum-engineering majors.

Is it “worth it” to spend the time and money for a degree in petroleum engineering? If you can do it, probably “yes.” But is it “worth it” to get a counseling degree? That’s far from clear.

Also, students who are considering college should not be misled by the supposed fact that, as Hargis stated, “90 percent of the fastest-growing jobs will require a college degree.” That idea was refuted years ago. The most recent projections for job growth show that most of the country’s employment growth will be in fields where advanced academic preparation is not needed.

According to the Oklahoma Employment Security Commission, for the decade 2008-2018, among the 20 occupations expected to have the greatest number of job offerings, only five (teachers, accountants, registered nurses, licensed practical nurses, and general managers) require education beyond high school.

An individual should not make decisions based on aggregate data, but rather on data pertinent to his or her particular circumstances. Consider Sue, who will soon finish high school. Should she go to college? The median earnings for Americans who have already gotten college degrees are irrelevant to her. She needs to think about the present.

She also needs to think about the cost of college and her own prospects, given her abilities. Nothing in the BLS chart sheds any light on her specific costs-versus-benefits comparison.

Going to college is not a “no-brainer.”

George Leef (J.D., Duke University) is director of research at the John William Pope Center for Higher Education Policy. He is the author of Free Choice for Workers: A History of the Right-to-Work Movement (2005) and editor of Educating Teachers: The Best Minds Speak Out (2002).

Jenna Ashley Robinson (Ph.D. candidate in political science, UNC-Chapel Hill) is the Pope Center’s campus outreach coordinator.