Police discrimination has been a hot-button issue in the U.S. for decades and now, new research shows that it continues to this day in shocking amounts.

A Stanford University research study took a look into the police biases across North Carolina when it comes to race-related traffic stops.

“Our threshold test suggests that officers apply a double standard when deciding whom to search,” said Camelia Simoiu, Stanford graduate student. “With black and Hispanic drivers searched on the basis of less evidence than whites and Asians. We consistently observe this pattern of behavior across the largest 100 police departments in the state.”

According to the North Dallas Gazette, the researchers took data from 4.5 million traffic stops in 100 cities across North Carolina over a period of six years. The study shows that even though blacks and Hispanics are more likely to be searched, the chances of discovering weapons or illegal drugs is actually more prevalent in white and Asian vehicles.

The study found discrimination against blacks in 57% of the departments involved.

During the study, according to PINAC, over 2.2 million whites were stopped, 1.8 million blacks, nearly 400,000 Hispanics, and almost 70,000 Asians. The search rate for the black drivers was the highest at 5.4%, followed by Hispanics at 4.1%. White drivers were only searched at a rate of 3.1% and only 1.7% for Asian drivers.

“We cannot, however, definitively conclude that the disparities we see stem from racial bias,” the researchers said in their study. “For example, officers might instead by applying lower search thresholds to those from lower socio-economic backgrounds, a demographic that is disproportionately black and Hispanic.”

Nationwide, drivers are pulled over for various reasons, including failure to wear seat belts, which 18- to 34-year-old men being the most likely to not wear their seat belts. Some of the irregularities found in the North Carolina study reflect that of the entire country. Stanford researchers are continuing their study and are currently accumulating data from many other states.

“We hope our results spur further investigation into allegations of police discrimination and help improve public policy,” said Sharad Goel, assistant professor of management science and engineering at Stanford and the faculty lead on the study.