"When mental rotation ability was factored out of the analysis, there was still a sex difference in time taken to construct the furniture, but the sex differenc

"When mental rotation ability was factored out of the analysis, there was still a sex difference in time taken to construct the furniture, but the sex difference in the accuracy of the construction disappeared, which certainly suggests that one reason the male participants may have outperformed their female peers is because they tended to have superior mental rotation abilities, likely making them less dependent on the visuals in the instructions." How would a researcher factor out mental rotation ability after the fact?