That noise is Harriet Harman grinding her teeth about new research that – let’s face it – is bound to be interpreted by diversity dinosaurs as evidence that companies should think twice before adding more women to the board.

The good news: the paper in the Journal of Financial Economics finds that female directors of US companies “are not mere tokens” and bring “new ideas and different perspectives” to boards. Their zeal for monitoring executives does add value to companies with weak governance. The bad news: the oft-cited correlation between strong female representation on boards and corporate outperformance doesn’t hold up at companies with strong governance.