Cervical cancer is 77 percent more deadly for black women and 44 percent more deadly for white women than previously thought, researchers report today in the journal Cancer.

But the lethal boosts aren’t from more women actually dying than before—they’re from scientists correcting their own calculation error. In the past, their estimates didn’t account for women who had undergone hysterectomies—which almost always removes the cervix, and with it the risk of getting cervical cancer.

“We don’t include men in our calculation because they are not at risk for cervical cancer and by the same measure, we shouldn’t include women who don’t have a cervix,” Anne F. Rositch, the study's lead author and an epidemiologist at Johns Hopkins told The New York Times.

For the study, the researchers looked at national cervical cancer mortality data collected between 2000 to 2012. They also looked into national survey data on the prevalence of hysterectomies. Then, they used those figures to adjust the number of women at risk of dying of cervical cancer.

The researchers found that black women have a mortality rate of 10.1 per 100,000. For white women, the rate is 4.7 per 100,000. Past estimates had those rates at 5.7 and 3.2, respectively. The new death rate for black women in the US is on par with that of developing countries.

Though the new study wasn’t designed to address racial disparities, experts speculate that the large difference reflects unequal access to preventative medicine and quality healthcare.

Cervical cancer is highly preventable. Most cases are caused by sexually transmitted infections with human papillomavirus (HPV), for which there is a vaccine. And with recommended screening and monitoring, the development of cancer can easily be avoided.

For 2016, experts estimated that nearly 13,000 American women would be diagnosed with cervical cancer and more than 4,000 would die from the disease.

Cancer, 2017. DOI: 10.1002/cncr.30507 (About DOIs).