Any study can find whatever the researcher is looking for.
Are there wage gaps? Yup. And it's common sense why.
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It's not easy to hire the best person for the job, but you want whomever is the best that you can afford. Even Steve had issues finding the best. Notice not once did he mention anything regarding color, sex, who they choose to have sex with, etc.
You don't need a study to figure out common sense. (Unless you are in government then you need a study on everything and completed in triplicate...)