Northamptonshire Police has been called out by inspectors for not understanding why they are using stop and search powers on certain members the public.
The force has slipped from "good" to "requires improvement" in its latest 'legitimacy report', which looks into how fairly it treats the public and its staff after an inspection in June.
The report, published on December 12, says officers do not understand "the reasons why black people are more likely to be stopped and searched than white people".
More also needs to be done to support communities with less confidence in the police and review how it supports its own staff suffering from work-related stress, as well as how it deploys pregnant officers.
The report reads: "Much of the operational workforce is yet to do[...] training on unconscious bias.
"The force cannot produce data on how many of its workforce have received training on important aspects such as understanding unconscious bias.
"In 2015/16 in the local population of Northamptonshire Police, black, Asian and minority ethnic (BAME) people were three times more likely to be stopped and searched than white people. Black people were five-and-a-half times more likely to be stopped and searched than white people.
"The force [...] need to do more work to understand the reasons behind this."
The report also encourages Northamptonshire Police to take feedback from people who are stopped and searched or have complained about their treatment in such an incident, calling it a "missed opportunity" to improve.
However, the force was praised as the only service in the UK to show it had good reason for every stop and search incident in 2017, with over a quarter of them resulting in an item being found by officers.
It also has an "impressive" independent panel made up of members of the public to scrutinise the force's stop and search habits, although more needs to be done to look at the patterns created and not just individual cases.
But the workforce of Northamptonshire Police's say they do not feel able to raise questions with their chief inspectors and superintendents and were happier to raise issues with their chief officers first.
Chief Constable Simon Edens: “While it is disappointing to have fallen behind in two of the three areas inspected, I’m confident that we had already identified many of the issues raised and begun to address them.
“The Chief Officer team care passionately for the people we work with and want to ensure they are confident and well-equipped to serve the public of Northamptonshire to the very best of their ability.”
The inspection came as part of a national annual review of the public's confidence in the police.