From the 1970s to the 1990s, the share of students leaving college with a degree steadily declined. But according to a paper in the American Economic Journal: Applied Economics, the trend since then has taken a turn for the better.

Authors Jeffrey T. Denning, Eric R. Eide, Kevin J. Mumford, Richard W. Patterson, and Merrill Warnick documented a large increase in graduation rates over the last three decades. By digging into the records of nine large public universities, a public liberal arts college, and a nationally representative survey, the researchers concluded that grade inflation is the most likely driver, ruling out explanations such as better student preparation.

Denning says that more research is needed to determine whether this grade inflation is beneficial on the whole. But it should be something that school administrators consider when making decisions about grading standards.

Denning recently spoke with Tyler Smith about the impact of grade inflation on college completion rates and the upsides it has as a policy tool.