Please answer a question about the following article about Jehovah%27s Witnesses:

A sociological comparative study by the Pew Research Center found that Jehovah's Witnesses in the United States ranked highest in statistics for getting no further than high school graduation, belief in God, importance of religion in one's life, frequency of religious attendance, frequency of prayers, frequency of Bible reading outside of religious services, belief their prayers are answered, belief that their religion can only be interpreted one way, belief that theirs is the only one true faith leading to eternal life, opposition to abortion, and opposition to homosexuality. In the study, Jehovah's Witnesses ranked lowest in statistics for having earned a graduate degree and interest in politics.

Jehovah's Witnesses in the United States ranked highest in people whose education extended no further than what?
high school graduation