According to a new report by the U.S. Centers for Disease Control and Prevention, the death rates for black americans dropped substantially –  25 percent between 1999 and 2015, which narrowed the gap in the death rate between white and black Americans from 33 percent in 1999 to 16 percent in 2015.

The report didn’t explore why the gap narrowed so significantly but one of the report’s authors speculated that black people have benefiting from decreases in certain diseases, including AIDS and tobacco-related illnesses.

According to the study, the change was most striking among those 65 and older. In that group, the death rate for black people fell 27 percent, compared to 17 percent for white people. Again, the researchers didn’t study why, but in various news outlets the report’s author has said that overall increases in socio-economic status of older black Americans – who were very young adults during the civil rights era – may have something to do with it.

All is not ideal for black Americans, however. Black Americans have an overall life expectancy that’s still four years less than white Americans. And younger black people are still developing, and dying from, major health problems that typically affect older people:  high blood pressure, diabetes, heart disease and stroke.

The authors concluded that there’s still work to do:

To continue to reduce the gap in health disparities, these findings suggest an ongoing need for universal and targeted interventions that address the leading causes of deaths among blacks (especially cardiovascular disease and cancer and their risk factors) across the life span and create equal opportunities for health.

Read the full report here.