The biggest reason is illiteracy.

VOA: special.2010.11.08

Throughout the world, there are literacy and illiteracy substantial problem.

世界上存在很多,文化素养以及文盲的问题存在。

麻省理工公开课 - 媒体、教育、市场课程节选

Is the probably illiteracy confined to third-world developing countries?

是否文盲只在,第三世界的发展中国家存在呢？

麻省理工公开课 - 媒体、教育、市场课程节选

"Over the last few months, there have been a number of training centers open that are exclusively for members of both the Afghan National Army and the Afghan national police force, and I would say that drug usage and illiteracy are two of the big problems within the security forces that NATO has really made a big priority now.

VOA: standard.2010.06.23

In 1992, a study on literacy of United States a particular illiteracy was associated with law incompetence, with poverty, with welfare, with incarceration.

992年，一项关于美国人文化素养的研究,文化素养低下与,低下的生活水平，贫困和社会福利，以及监禁有一定关系。

麻省理工公开课 - 媒体、教育、市场课程节选