Searching by textword can supplement a search by MeSH headings
To increase the sensitivity of a search, use the "explode" command and avoid using subheadings
Scan titles on screen rather than relying on the software to find the most valid or relevant ones
In 1928, in his introduction to Sceptical Essays, Bertrand Russell wrote: "The extent to which beliefs are based on evidence is very much less than believers suppose." Medical beliefs, and the clinical practices that are based on them, are a case in point. Debate continues as to whether scientific evidence alone is sufficient to guide medical decision making, but few doctors would dispute that finding and understanding relevant research based evidence is increasingly necessary in clinical practice. This article is the first in a series that introduces the non-expert to searching the medical literature and assessing the value of medical articles.
Articles can be traced in two ways: by any word listed on the database, including words in the title, abstract, authors' names, and the institution where the research was done; and by a restricted thesaurus of medical titles, known as medical subject heading (MeSH) terms.
To illustrate how Medline works, I have worked through some common problems in searching. The scenarios have been drawn up using OVID software.
Table 1. Useful search field suffixees (OVID)
Thus, to find a paper called something like "Confidentiality and patients' casenotes," which you remember seeing in the British Journal of General Practice a couple of years ago, (1) type the following sequence:
2 british journal of general practice.jn
3 1 and 2
You could do all this in one step:
1 confidentiality.ti and british journal of general practice.jn
This step illustrates the use of the boolean operator "and"; it will give you articles common to both sets. Using "or" will simply add the two sets together.
Note that since 1988 the British Medical Journal is abbreviated BMJ in OVID software, and Journal of the American Medical Association is JAMA. Other useful field suffixes to try when searching for a known article are author (using the syntax haines-ap.au), institution (for example, manchester.in), or title (for example, evidence-based medicine.ti).
1 anorexia nervosa
You have not typed a field suffix (such as .tw), so the OVID system will automatically try to "map" your request to one of its standard medical subject headings (abbreviated MeSH and colloquially known as "mesh terms"). (Note that not all Medline software packages will automatically map your suggestion to MeSH terms. With Silver Platter search software, for example, you need to enter your heading and click the "suggest" button.) For this example, the screen offers you either "eating disorders" or "anorexia nervosa" and asks you to pick the closest one. Choose "anorexia nervosa" (space bar to highlight the text, then press "return").
The screen then asks you whether you want to "restrict to focus." Do you only want articles which are actually about anorexia nervosa, or do you want any article that mentions anorexia nervosa in passing? Let's say we do want to restrict to focus. Next, the screen offers us a choice of subheadings, but we'll ignore these for a moment. Select "Include all subheadings." We could have got this far using a single line command:
2 *anorexia nervosa/
The * shows that the term is a major focus of the article, and the / represents a MeSH term. You should have about 750 articles in this set.
Similarly, to get articles on osteoporosis (which is also a MeSH term), use the following single line command:
You should get about 2200 articles. Note that in OVID, if you know that the subject you want is an official MeSH term, you can shortcut the mapping process by typing a slash (/) after the word. Note also that we have not used an asterisk here, because osteoporosis may not be the focus of the article we are looking for.
Finally, put in the term "oral contraceptives" (without an asterisk and without a slash) to see what the MeSH term here is. You will be offered "contraceptives, oral," and if you had known this you could have used the following command:
4 contraceptives, oral/
This set should contain around 1200 articles. You can combine these three sets, either by using their set numbers 1 and 2 and 3 or by typing the single line command:
5 *anorexia nervosa/ and osteoporosis/ and contraceptives, oral/
With this you will have searched over 4000 articles and struck a single bull's eye. (2) (If you don't find it, check the syntax of your search carefully, then try running the same search through the previous five year database using the Alt-B command.)
Table 2. Useful subheadings (OVID)
Table 3. Useful "limit set" options
The option "AIM journals" denotes all journals listed in the Abridged Index Medicus-that is, the "mainstream" medical journals. Alternatively, if you want articles relating to nursing, rather than medical care, you could limit the set to "Nursing journals." This is often a better way of limiting a large set than asking for local holdings. If you are not interested in seeing anything in a foreign language (even though the abstract may be in English), select this option, again bearing in mind that it is a non-systematic (indeed, a very biased) way of excluding articles from your set. (3
Note that instead of using the "limit set" function key you can use direct single line commands such as:
9 limit 4 to local holdings
10 limit 5 to human
1 (surrogate not mother$).tw
Deciding to use the "not" operator is a good example of how you can (and should) refine your search as you go along-much easier than producing the perfect search off the top of your head. I used the truncation symbol $ to find all words from a single stem, such as mother, mothers, motherhood, and so on.
Another way of getting rid of irrelevant articles is to narrow your textword search to adjacent words using the "adj" operator. For example, the term "home help" includes two very common words linked in a specific context. Link them as follows:
1 home adj help.tw
Another important strategy for preventing incomplete searches is to use the powerful "explode" command. The MeSH terms are like the branches of a tree with, for example, "asthma" subdividing into "asthma in children," "occupational asthma," and so on. Medline indexers are instructed to index items by using the most specific MeSH terms they can. If you just ask for articles on "asthma" you will miss all the articles indexed under "asthma in children" unless you "explode" the term using the following syntax:
1 exp asthma/
1 ptx stress
The screen shows many options, including posttraumatic stress disorders, stress fracture, oxidative stress, stress incontinence, and so on.
The command "ptx" is useful when the term might be found in several subject areas. If your subject is a discrete MeSH term, use the tree command. For example:
2 tree epilepsy
will show where epilepsy is placed in the MeSH index-as a branch of "brain diseases," which itself branches into generalised epilepsy, partial epilepsy, post-traumatic epilepsy, and so on.
These EBQFs (evidence based quality filters), which are listed in Appendix 1, are complex search strategies developed by some of the world's most experienced medical information experts. You can copy them into your personal computer and save them as strategies to be added to your subject searches. Other search strategies that will identify cohort studies, case-control studies, and so on will soon be available from the UK Cochrane Centre, Summertown Pavillion, Middle Way, Oxford OX2 7LG (firstname.lastname@example.org).
Appendix 1 and 2
If you wish to broaden your search to other electronic databases, ask your local librarian where you could access the following:
- AIDSLINE-Covers AIDS and HIV back to 1980.
- Allied and Alternative Medicine-Covers complementary and alternative medicine.
- American Medical Association Journals-Provides the full text of JAMA plus 10 specialty journals produced by the American Medical Association; from 1982.
- Assia-An applied social sciences database covering psychology, sociology, politics, and economics since 1987. All documents have abstracts.
- Cancer-CD-A compilation by Silver Platter of Cancerlit and Embase cancer related records from 1984. The CD Rom version is updated quarterly.
- Cinahl-The nursing and allied health database covering all aspects of nursing, health education, occupational therapy, social services in health care, and other related disciplines from 1983. The CD Rom version is updated monthly.
- Cochrane Library-The Cochrane Controlled Trials Register (CCTR), Cochrane Database of Systematic Reviews (CDSR), Database of Abstracts of Reviews of Effectiveness (DARE), and Cochrane Review Methodology Database (CRMD) are updated quarterly; authors of systematic reviews on CDSR undertake to update their own contributions periodically. (4)
- Current Contents Search-Indexes journal issues on or before their publication date. It is useful when checking for the very latest output on a subject. Updated weekly; from 1990.
- Current Research in Britain-The British national research database of trials in progress.
- DHData (formerly DHSS-Data)-The database of the UK's Department of Health indexes articles covering health service and hospital administration; from 1983.
- Embase-Focuses on drugs and pharmacology but also includes other biomedical specialties. It is more up to date than Medline and has better European coverage. The CD Rom version is updated monthly.
- Helmis-The Health Management Information Service at the Nuffield Institute of Health, Leeds, UK, indexes articles on health service management.
- Psychlit-Produced by the American Psychological Association as the computer searchable version of Psychological Abstracts; covers psychology, psychiatry, and related subjects; journals are included from 1974 and books from 1987 (English language only).
- Science Citation Index-Indexes references cited in articles as well as the usual author, title, abstract, and citation of articles themselves. Useful for finding follow up work done on a key article and for tracking down addresses of authors.
- Share-Based at the King's Fund library in London; published and ongoing research into the health of, and health services for, black and minority ethnic groups.
- Toxline-Information on toxicological effects of chemicals and drugs on living systems; from 1981.
- Unicorn-The main database of the King's Fund, London. Covers health, health management, health economics, and social sciences. Particularly strong on primary health care and the health of Londoners.
Thanks to Mr Reinhard Wentz, Ms Jane Rowlands, Ms Carol Lefebvre, and Ms Valerie Wildridge for advice on this chapter. I am grateful to Carol Lefebvre of the UK Cochrane Centre for permission to reproduce the EBQFs in Appendix 1 (**).
The articles in this series are excerpts from How to read a paper: the basics of evidence based medicine. The book can be ordered from the BMJ Bookshop: tel 0171 383 6185/6245; fax 0171 383 6662. Price [pound sign]13.95 UK members, [pound sign]14.95 non-members.
2. Seeman E, Szmukler GI. Formica C, Tsalamandris C, Mestrovic R. Osteoporosis in anorexia nervosa: the influence of peak bone density, bone loss, oral contraceptive use, and exercise. J Bone Mineral Res 1992;7:1467-74. [Back to The Medline database:Problem 2: You want ..:Solution: Construct ..]
3. Moher D, Fortin P, Jadad AR, Juni P, Klassen T, Le Lorier J, et al. Completeness of reporting of trials published in languages other than English: implications for conduct and reporting of systematic reviews. Lancet 1996;347:363-6. [Back to The Medline database:Problem 3: You want ..:Solution: Use subhea..]
4. Bero L, Rennie D. The Cochrane Collaboration: preparing, maintaining, and disseminating systematic reviews of the effects of health care. Jama 1995;274:1935-8. [Back to The Medline database:Problem 8: Medline h..:Solution: Explore ot..]