Editor’s Note: This is the first article of a two-part series. The other article is “What Learning Science Says About Improving Online Courses.”

Universities have been teaching online for more than 30 years, and professors and colleges who pioneered the approach have done plenty of research over that time hoping to find what works best. So what are the major lessons learned, and how can people just starting online programs build on that foundation?

In medicine, clinicians are generally guided by research that has followed large groups of patients over long periods of time. The Framingham Heart Study, for instance, has followed generations of patients since 1948 and has steered the decisions of doctors who are trying to prevent and treat heart disease.

Unfortunately, there isn’t a perfectly analogous study in online higher education. But there have been a few meta-studies that attempted to draw conclusions from hundreds of smaller investigations.

Much of the earliest research into online learning focused on whether it was as good as classroom teaching. In its early years, there was skepticism about online teaching across higher education, even though online education built on the existing foundation of correspondence courses and degrees like those offered by Britain’s Open University, where students originally learned via old-fashioned snail mail—sending assignments in an envelope and getting back graded papers the same way.

By 2001, an analysis of more than 300 studies found that teaching online could be as effective as in-person education, boasting that there was “no significant difference” between the two modes, if done well. While “we’re not worse!” may seem like a timid rallying cry, the research helped convince many college leaders to continue or expand their digital-education experiments.

More recently, questions turned to which types of online teaching worked better than others. For instance, is blended learning—where some learning takes place in person and some online—more effective than a purely online approach? A 2010 “meta-analysis” by the United States Department of Education found there was not yet enough evidence to say whether all-online education or blended education efforts were a better option, but it did attempt to offer a breakdown of promising approaches. It found that “on average, students in online learning conditions performed modestly better than those receiving face-to-face instruction.”

Even those studies are quick to point out that there may never be an easy answer to which techniques work best. Those who try to measure which teaching methods are more effective quickly find themselves sinking into a morass of variables—the quality and training of the instructors, the preparation of the students, the availability of support services outside of the classroom, and more.

That said, here’s some evidence-based advice, drawn from reading some of the available research and interviews with long-time online-learning leaders.

First, decide whom you want to reach.

A key decision when setting up online programs is, Whom do you want to reach?

Southern New Hampshire University’s campus programs serve 18- to 22-year-olds who want a campus experience. But when the university decided to move into online programs back in the 1990s, they decided to target a new audience—“adult students”—who are often already working or raising families and trying to finish their degrees. Many of those students are in the military and looking for education but not able to get to a campus.

Brian Fleming, executive director of an innovation center at Southern New Hampshire University, called the Sandbox ColLABorative, says that a common mistake when setting up programs online is assuming that if you build them, students will come. But to reach students who aren’t able to get to campus, new supports need to be created, and marketing efforts. “It’s a pretty big investment for schools,” he says.

Tax records for the university reveal that in 2015, Southern New Hampshire spent more than $37 million on television, radio and Internet advertising to recruit students. That investment has paid off, as the university’s online programs have grown from about 8,000 students in 2001 to more than 100,000 students today, most of them adult students.

Fadl Al Tarzi, who leads a startup online institution called Nexford University that hopes to serve students in the Middle East, Asia, and Africa from its base in Washington, D.C., agreed. “Try to analyze why your students or your learners are going online, and design a product that’s fit for purpose rather than a digitized version of your existing model,” he says.

For Nexford, the focus is business degrees, with plans to deliver lower-cost MBAs and undergraduate business degrees aimed at “middle-income markets of the world,” in countries where it is difficult or impossible for parents to send their children abroad to study.

Because the online audience—and the services and support they require—can be so different, Fleming and other college leaders recommend considering turning to an outside company to help run online programs, if an institution can afford such a service. Those companies are called online program managers, or OPMs, and one online consulting firm recently published an overview of the various providers and what to look for.