Socioeconomic factors mean the specific circumstances which inhibit an individual's abilities or opportunities based upon their financial viability and social standing. When people have fewer opportunities due to social problems, this is due to lack of education, which can often mean that a child is not encouraged to attend school to learn, or their parents have health or addiction problems resulting in a lack of inspiration or motivation to widen opportunities. As socioeconomic factors increase (limiting access to opportunities) so illiteracy rates rise.
I would have to say parentheses, since its not restricted.
