Only 0.8% of married couples where the stay-at-home father was out of the labor force for a year.

疑问：此处的where the stay-at-home father是个句子吗？不是句子的话，where又是什么词性以及有什么含义？有些想不明白

以下是有关此句的上下文：

The endless debate about “work-life balance” often contains a hopeful footnote about stay-at-home dads. If American society and business won’t make it easier on future female leaders who choose to have children, there is still the ray of hope that increasing numbers of full-time fathers will. But based on today’s socioeconomic trends, this hope is, unfortunately, misguided.

    It’s true that the number of men who have left work to do their thing as full-time parents has doubled in a decade, but it’s still very small: only 0.8% of married couples where the stay-at-home father was out of the labor force for a year. Even that percentage is likely inflated by men thrust into their caretaker role by a downsizing. This is simply not a large enough group to reduce the social stigma (污名) and force other adjustments necessary to supporting men in this decision, even if only for a relatively short time.