Another aspect of the genuine material factor (GMF) defence was scrutinised in Blackburn v Chief Constable of West Midlands Police, a recent decision of the Employment Appeal Tribunal (EAT). This time the decision of the employment tribunal, which had concluded that the adverse impact on women of special payments for night work could not be justified, was overturned. The EAT concluded that rewarding police officers who were available to work at night was a legitimate aim, and that the method chosen to achieve it - extra payments worth on average around £750 a year - was proportionate. The Equal Pay Act did not require the employers to pay women who could not work at night the same as their male comparators who could, and the fact that another method of rewarding night work could have been adopted was not relevant.

The EAT appears to have been influenced by the fact that the statistical evidence of disparate impact (a difference of just over 5 percentage points) was not that striking. If there had been a bigger statistical disparity, the employer's appeal might not have been successful.

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