Earnings data the U.S. Department of Education released Thursday show that graduates of certificate programs at public institutions earned nearly $9,000 more than graduates of those programs at for-profit colleges.

The department will use the new numbers to enforce its gainful employment rule, which was finalized in 2014 and seeks to measure whether a sufficient number of graduates of vocational programs can repay their federal loans.

The data also showed a wide range of variation in earning outcomes depending on a graduate’s field of study. That variation partly explains the difference in earnings between certificate holders who attended public and for-profit colleges. Those who attended higher-earning certificate programs were more likely to have attended a public institution, such as a community college.