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When you have a better idea of a possible direction to take your search in, try running it in Summon using some of the terms you have found during your search in reference materials. Remember as well to apply some limits. Go to the left hand column and examine the different kinds of limits that can be used.
Scholarly and Peer-reviewed - when you limit by this, you are mostly restricting the search to journal articles. Read more about Scholarly Articles here
Date range - there are preset ranges (12 months, 3 and 5 years) you can pick OR enter your own dates
Discipline - you can choose more than one if you like - the number next to the Discipline shows how many articles are classed in that discipline - there can be overlap among disciplines.
Subject Terms - these are assigned by the journal publishers. There is no thesaurus of consistent subject terms in summon. Therefore it is usually best to choose a number of headings which cover aspects of your search. This an EXCELLENT way of narrowing and focussing your search. You usually have to click the MORE button to bring up all the subject terms. When you get the full list it will look like this (Please note that as you add more subject terms you are not narrowing the search by all the terms (which is a Boolean "AND" search; you are creating a Boolean "OR" search)
When you have looked at scholarly journal articles for your time period and discipline, Go back and unclick Scholarly and Peer Reviewed. Try some other Content filters - for instance Book/Ebook (explained more on this tab)or Magazine Article. When you do this, recheck the Subject Terms to see if some new terms have been added which better address the focus you are taking.
Related Articles - when you get your search results, another way to find pertinent articles is to use the Related Articles function.