It has been pointed out by modern research that in these books, mixed with the folklores, ghost stories and essays of classical Japanese culture, there are many yokai characters that are considered to be inventions that did not exist in the classical Japanese culture.
しかし、それら書籍中の妖怪には、古典の民間伝承、怪談、随筆などのものに混じり、古典上に存在しない創作物と思われる妖怪が多いことが現代の研究により指摘されている。