A key step in writing the literature review is working out what literature should be included. You should only use literature that is highly relevant to your topic. It is better to select a limited number of sources that are central to your topic rather than trying to collect a large number of sources that are not as closely connected.
You may also need to justify why you have included some works and not others. For example, some studies may be superseded by recent evidence or theories and are now out of date. Primary sources are preferred over sources that another person had cited (secondary sources). If you do come across a useful secondary source, try to find the primary source it is referring to, so that you can read it first-hand.
Use the following resources to help you test and evaluate the literature you find.