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In a standard literature search, relevant hits are retrieved with a search query that is as precise as possible. The systematic literature search, on the other hand, should be so broad that all potentially interesting literature on a topic is retrieved. The art here is to phrase the search terms in an appropriately broad way, without getting too many non-relevant hits.
A systematic search begins with well-structured preparation: each scientific question can be broken down into individual aspects. For each aspect / concept it is checked if thesaurus terms (subject headings) are available and which synonyms / expressions have to be searched. Thus, a search string is created for each concept.
When searching systematically, one must not limit oneself to the focused search with subject headings, but must always supplement this with a free text search. To keep the relevance reasonably high, the phrase search is a good choice. However, this method can prove to be too restrictive.
Proximity operators can be used to enforce proximity in a search with multiple terms, which increases the hit relevance considerably compared to a simple AND operation.
Proximity operators are available in many large databases:
| Database/Provider | Order of Appearance |
Terms |
|
|---|---|---|---|
| open | fixed | ||
| Cochrane Library | NEAR/n | NEXT/n | n |
| EMBASE | NEAR/n | NEXT/n | n |
| Medline (EBSCOhost) | Nn | Wn | n |
| Medline (Ovid) | adjn | n.a. | n |
| Medline (Proquest) | NEAR/n or N/n | PRE/n or P/n | n-1 |
| PubMed | [Title/Abstract:~3] | n.a. | n |
| Scopus | W/n | PRE/n | n |
| Web of Science | NEAR/n | n.a. | n |
Database-specific codes can be replaced with Find & Replace commands in a Word template. Subject headings are also database-specific: in each thesaurus (=heading catalog) it must be determined anew whether suitable terms are available. If the strategy is transferred to a database without heading search (e.g. Web of Science), the headings are simply omitted and only the free text search will be applied.
It should be possible to repeat a systematic search at any time. Therefore, a precise description and documentation of the employed search strategy are essential. Most of the time it is not possible to closely document a search query with words alone. Supplement the description of the search in the methodology section of your paper/research with detailed documentation of the search strategy for at least one database in the appendix.
