Complex sentence: Premenstrual dysphoric disorder (PMDD) is a more severe form of PMS that has greater psychological symptoms, and which affects three to eight percent of pre-menopausal women.
Split into simpler sentences: Premenstrual dysphoric disorder (PMDD) is a more severe form of PMS that has greater psychological symptoms. PMDD affects three to eight percent of pre-menopausal women.