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There are many different online resources including catalogues, databases and
the internet, with many different software interfaces. Some will offer more
sophisticated features than others.
As an example consider a search for information using the Medline database.
Many of the principles are applicable to other resources, such as the library
catalogue.
Define the subject area
Write down your query and identify the key concepts. For example, you may want
to find journal articles on the role of vitamin C in the prevention of cancer.
The key concepts here are: vitamin C, cancer; and prevention.
Find suitable search terms
Translate these concepts into terms that the system you are using will understand.
Many databases (e.g. Medline) use a system of subject headings - a controlled
list of terms assigned by indexers to each record to describe the content of
the article. Other databases (e.g. the Science Citation Index, Web of Science)
only allow you to search for words occurring within the text of the record (free
text searching: see below).
Subject Headings
Different authors often use a variety of terms to describe the same concept.
One author might use the term "cancer", another might refer to "carcinoma"
and a third might write about "neoplasia". In Medline, each of these
papers would be assigned the single subject heading "Neoplasms". By
searching for this single subject heading, you will retrieve all the papers
which discuss this topic, regardless of the different vocabulary used by the
different authors. Many databases offer considerable guidance with selecting
an appropriate subject heading. The Ovid interface to Medline for example will
suggest a list of possible subject headings. After selecting one of these, you
will have the opportunity to select a broader or more specific subject heading
so that you can reflect your topic more precisely.
Free text searching
Sometimes no subject heading exists to describe your topic. Some databases
do not use subject headings at all. In these cases, you will need to use the
'free text' approach to searching. Before you search, think about all the possible
ways an author might have described their subject, as for example, in the different
terms for cancer. Bear in mind the following:
Synonyms e.g. (cancer/carcinoma)
Spelling variants - particularly US and UK spelling conventions (e.g. ischaemia/ischemia)
Single/plural forms (e.g. heart attacks/heart attack)
Ambiguity (e.g. a simple free text search for AIDS will retrieve papers not
only about Acquired Immune Deficiency Syndrome but also on aids to recovery,
hearing aids, walking aids etc.)
There are a number of ways of overcoming these problems:
Truncation
Most databases allow you to use wildcards (to allow for variant spellings),
or truncation characters to search on the stem of the word.
For example in Ovid Medline you can use "?" to stand for 0 or 1 characters,
so that isch?emia would find "ischaemia" or "ischemia"
and "$" for truncation,
so that pattern$ will retrieve "pattern", "patterns" and
"patterning".
Combining searches
Separate searches on different concepts can be combined using the operators
AND and OR.
In some databases (e.g. Web of Science) you will need to construct a complete
search statement with ANDs and ORs etc. in one go. In others, including Ovid
Medline, it is important to search on each different concept separately and
then combine the search results.
OR
Using OR will retrieve records in which one or more of the specified terms appears.
You might have searched for pregnancy and searched for childbirth. By combining
these searches using OR, you will retrieve papers where EITHER "pregnancy"
occurs OR "childbirth" or both terms may appear in the same record.
AND
Combining searches using AND will retrieve records in which all of the specified
terms appear in each record found.
You might search for myocardial infarction and tobacco smoking.
By combining these searches using AND, you will retrieve ONLY those papers where
BOTH these terms occur together.
Use OR to link each set which describes the same concept. Use AND to link different
concepts.
For example, you are looking for papers on the relationship between diet and
life expectancy.
You decide to search for the following terms to represent the concept of diet:
'diet', 'nutrition', 'eating habits'; and for the following terms to represent
the concept of 'life expectancy': 'life expectancy' and 'longevity'.
Your search history on Medline might look like this:
Note that "eating habits" maps to the Medical Subject Heading "Food
habits"
Searches 1 to 3 (diet, nutrition, food habits) represent the concept of diet,
whilst searches 4 to 5 (longevity, life expectancy) represent the concept of
longer life.
Use OR to create a single search set for each separate concept:
1 or 2 or 3 i.e. diet or nutrition or food habits
4 or 5 i.e. longevity or life expectancy
Use AND to create a set of references to papers which discuss both concepts
together:
6 and 7
Refine your search
Now look at your results to see how many records you have retrieved and how
relevant they are.
Too many records?
If you have found too many records consider how you can restrict or limit your
search
Major subject headings
Some databases distinguish between subject headings describing the main focus
of the article and those describing more peripheral topics. You can often restrict
your results to only those papers where your subject appears as the main topic.
In Ovid Medline, this is the 'Focus' option.
Subheadings
Medline and other databases offer a set of broad topical subheadings to allow
you to retrieve papers which discuss specific aspects of your subject e.g. adverse
effects; diagnosis; etc. Use these to make your search more specific.
Search by field
When free text searching in a database you usually, by default, search each
entire record for the terms you have specified. However, records on a database
are divided into fields. Most databases will allow you to specify that you only
want to search in a particular field or combination of fields. E.g. you could
specify that you only want to retrieve records which include your search term
in the title.
Limits
You can usually restrict your searches by year, by language or other limits.
Use more specific terms.
Using very broad terminology such as "Cancer" or "Diabetes"
will inevitably retrieve vast numbers of records. Try to be as specific as you
can.
Too few records?
Explode
Databases using subject headings often have an "Explode" facility.
The effect of this is to search not only for your selected subject heading,
but also any more specific subject headings listed in the database.
Use broader terms
Using highly specific vocabulary might have the effect of retrieving very few
records or none at all. Are there any more general terms to use?
Add synonyms
If you are free-text searching, try to think of alternative vocabulary to describe
your topic.
Remove limits
If you have specified various limits, such as year range, try removing them
or broadening them. Avoid selecting too many limits at once.
Finally, remember:
Evaluate
Evaluate the relevance of your search results. It is not only the number of
records found that is important. You will need to examine the records you have
found to see whether they are relevant to your search question. Bibliographic
databases such as Medline nearly always contain abstracts for most of the papers
indexed. An abstract is a brief summary of the content of a paper. It is an
informative condensed representation of that document reflecting the aims, methods
and results of the research. It can be used to judge whether it is relevant
to your needs.
Quality
Before an article can be published in an academic journal it has to go through
a procedure known as peer review. A number of experts in the field are asked
to critically appraise the article and advise on whether it should be published
in the particular journal to which it has been submitted. Reviewers use both
scientific and ethical criteria. The peer review process is an important check
on the publication of spurious information or badly performed research. However,
you should still exercise your own critical faculties in assessing the work.
Publication date
Do take into consideration the date when the article was published. In fast
moving fields it is important to discover the latest developments. When searching
Ovid Medline the results will always be presented in reverse date order (i.e.
latest first). Not all databases will provide this facility, so consider sorting
your results by date. Sorting Library catalogue results by date for example,
will ensure that you find the latest edition of a textbook.
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