Source: https://www.cambridge.org/core/journals/journal-of-biosocial-science/article/biosocial-correlates-of-age-at-first-sexual-intercourse-the-case-of-grade-9-and-grade-11-pupils-in-the-north-west-province-of-south-africa/ACF6F13F87C3FD38E0894BC0B5B79B74