Reasons for searching the literature:
1. to identify work already done or in progress that is relevant to your work;
2. to help to prevent you from duplicating what has already been done;
3. to avoid some of the pitfalls and errors of previous research;
4. to help you design the methodology for your project by identifying the key issues and data collection techniques best suited to your topic;
5. to enable you to find gaps in existing research, thereby giving you a unique topic.
(Hart, Chris. 2001. Doing a literature search:a comprehensive guide for the social sciences. London:Sage)