The correct answer is the second option (there is a difference in performance). The Equal Pay Act of 1963 was passed to ensure that employers would not discriminate based on gender. This means that employers cannot pay men more than women, just for being men (and vice versa). Essentially, the law ensures equal pay for equal work. However, it also notes that equal pay does not apply if the payment system correlates to the quantity of work. Since the women in this example are producing more output, then it is legal for them to be paid more for their larger quantity (and not simply because they are women).