一处关于数据的疑问

第一章靠近最后的一处讨论乱伦的数据听英语版书我没听明白，查了英文原文也没看明白(免费的只找到英文的)，不知道中文翻译的怎么翻的？

就是书中说 “当时标准的精神病学教科书称轮乱在美国非常罕见，发生概率大概是1/1百万。 当时美国女性人口只有一百万，我疑惑怎么47，几乎一半，找到了在医院地下室的我的诊室。”

47 的单位是什么？一百万的百分之47吗？不可能啊？！哪个数据的 "几乎一半" 啊？？

找到的英文版原文：

“as the standard textbook of psychiatry at the time stated that incest was extremely rare in the United States, occurring about once in every million women. Given that there were then only about one hundred million women living in the United States, I wondered how forty seven, almost half of them, had found their way to my office in the basement of the hospital.”

摘录来自: Bessel van der Kolk MD. “The Body Keeps the Score: Brain, Mind, and Body in the Healing of Trauma。” iBooks. ”

其中的 " forty seven, almost half of them", 我充满疑惑...