A legal expert is rejecting the legitimacy of research into police bias.

A two-year inquiry commissioned by police suggests there are ongoing inequities in treatment depending on people's race, sexuality, gender, and mental health.

It's found Māori men are more likely to be stopped, tasered, and prosecuted, compared with Pakeha.

Lawyer Steve Cullen says it's a 'bizarre' allegation.

"There might be individual cases that might seem to have that as a bias in relation to the parties involved in the case - but that doesn't support an allegation of fundamental corruption within the police nationwide."

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