Primary literature sources (also known as grey literature) are the first occurrence of a piece of work. They include
published sources such as reports, conference proceedings, theses. They also include unpublished manuscript sources
such as letters, and memos.
Secondary literature sources such as books and journals are the subsequent publications of primary literature.
These publications are aimed at a wider audience. They are easier to locate than primary literature as they are better
covered by the tertiary literature.
Tertiary literature sources, also called search tools, are designed either to help to locate primary and secondary
literature or to introduce a topic. They therefore include indexes and abstracts as well as encyclopedias and bibliog-
raphies.
Your use of these literature sources will depend on your research questions and objectives. For some research pro-
jects you may use only tertiary and secondary literature; for others you may need to locate primary literature as well.
7. It is important that you plan the literature search carefully to ensure that you locate relevant and up-to-date lit-
erature. This will enable you to establish what research has been previously published in your area and to relate your
own research to it. Time spent planning will be repaid in time saved when searching the literature. As you start to plan
your search, you need to beware of information overload! Before commencing your literature search you should under-
take further planning by:
• defining the parameters of your search;
• generating key words and search terms;
• discussing your ideas as widely as possible.
Techniques to help you in this include brainstorming and relevance trees.
8. Once obtained, the literature must be evaluated for its relevance to your research questions and objectives. The
following questions provide a checklist to help you in this process.
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How recent is the item?
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Have you seen references to this item (or its author) in other items that were useful?
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Does the item support or contradict your arguments? For either it will probably be worth reading!
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Does the item appeared to be biased? Even if it is it may still be relevant to your critical review!
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What are the methodological omissions within the work? Even if there are many it still may be of relevance!
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If the precision sufficient? Even if it is imprecise it may be the only item you can find and so still of relevance!
Your assessment of whether you have read a sufficient amount is even more complex. It is impossible to read eve-
rything, as you would never start to write your critical review. Yet you need to be sure that your critical review dis-
cusses what research has already been undertaken and that you have positioned your research project in the wider con-
text, citing the main writers in the field. One clue that you have achieved this is when further searching provides mainly
references to items you have already read. You also need to check what constitutes an acceptable amount of reading, in
terms of both quality and quantity, with your scientific advisor.