> Although the average woman’s salary in Britain is 29% lower than the average man’s, the bulk of that gap results from differences in rank within companies, firms’ overall compensation rates and the nature of the tasks a job requires.

If Software Engineer II makes less than Software Engineer III, and women of equivalent skill and experience to men have a significantly higher chance of being Software Engineer II than III, then the wage gap exists for "the same work".

This is particularly difficult to measure, but still possible with proper diligence, because rank throughout a career is a compounding advantage.

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