Medline searches

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The second-best method for finding evidence about treatment and the best source for finding most other types of best evidence in dermatology is by searching the Medline database on a computer.2,4 Medline is the National Library of Medicine's (NLM) bibliographic database covering the fields of medicine, nursing, dentistry, veterinary medicine, the healthcare system and the preclinical sciences. The Medline file contains bibliographic citations and author abstracts from approximately 3900 current biomedical journals published in the US and 70 other countries. The file contains approximately 9 million records dating back to 1966.125

Medline searches have inherent limitations that make their reliability less than ideal.2 For example, Spuls et al. conducted a systematic review of systemic treatments for psoriasis.6 Treatments analysed included UVB, PUVA, methotrexate, ciclosporin A and retinoids. The authors used an exhaustive strategy to find relevant references, including Medline searches, contacting pharmaceutical companies, polling leading authorities, reviewing abstract books of symposia and congresses, and reviewing textbooks, reviews, editorials, guideline articles and the reference lists of all papers identified. Of 665 studies found, 356 (54%) were identified by the Medline search (range 30-70% for different treatment modalities). No references beyond those identified by Medline searching were provided by the 17 of 23 authorities who responded.6

More than 20 vendors of Medline on line and on CD are available. Haynes et al. compared several vendors of Medline on line and on CD to determine which was best in terms of finding relevant articles and excluding irrelevant articles. Assessed on combined rankings for the highest number of relevant and the lowest number of irrelevant citations retrieved, SilverPlatter CD-ROM Medline clinical journal subset performed best for librarians searches, whereas PaperChase online system worked best for clinician searches. For cost per relevant citation, Dialog's Knowledge Index performed best for both librarian and clinician searches.7

Regardless of the platform used, the key to Medline searching is to find relevant articles and to exclude irrelevant citations. Several useful techniques can greatly aid your ability to accomplish this goal. Searches are generally done on the basis of boolean combinations of search terms. For example, our search for best evidence about drug treatment of onychomycosis might read [onychomycosis and (terbinafine or itraconazole or fluconazole) and not case reports].* This search would identify articles on onychomycosis using any of the listed drugs and excluding case reports.1,2

It is important to understand the difference between textword and MeSH searching and to be able to do both.2 Many of the programs used to search the Medline database automatically do textword and MeSH searches. MeSH terms include all of the terms in the medical subject headings, a controlled vocabulary of keywords used to index Medline. Each Medline citation is given a group of MeSH terms that relate to the subject of the paper from which it is drawn. Frequently, MeSH terms will have an additional subheading which further defines how the MeSH term relates to the article with which it is

*The convention used throughout for search entries is that Boolean operations within parentheses are done first.

associated.2 This subheading is appended to the MeSH term, for example "onychomycosis diagnosis".

Indexing articles is not an exact science. The MeSH headings assigned by the NLM may not coincide with the intent of the author or the majority of searchers for several reasons: authors may not clearly express their intent; indexers are usually not experts in the field of the article they are indexing; and the mistakes associated with doing repetitive tasks occur.2 Relevant articles may be missed when they are not assigned the appropriate MeSH heading. Irrelevant articles may be included in a MeSH search if they are assigned to the wrong MeSH heading. For example, the Cochrane Collaboration identified major problems in the Medline indexing of randomised controlled trials.2

Textword searches allow one to search articles for words within the title and abstract that are important to, and coincide with, the intent of the author. However, textword searches are subject to several problems - authors may not describe their methods or objectives well, or may make errors in spelling, omission or commission.2 The problem of misspelling can be illustrated by doing a textword search for "pruritis" (pruritus spelled incorrectly). This search yielded more than 40 references in which the word has been misspelled. Many of these references may not be detected in a search for pruritus (spelled correctly).2

Boolean topic searches will often contain too many or too few references. They may contain many irrelevant citations and miss many relevant citations. Several techniques will help make searches more sensitive (i.e. pick up relevant citations) and more specific (i.e. exclude irrelevant citations).2 To increase the sensitivity of searches, searching both textword and MeSH headings, exploding MeSH headings and using truncation may be helpful. MeSH term searches can be "exploded" to include all terms that are logical subsets of the term entered.2 For example, exploding the MeSH term "onychomycosis" will retrieve all the articles that use that MeSH term, whether they have subheadings or not. Many of the programs used to search the Medline database automatically explode searches of MeSH terms or MeSH major topics.

Truncation refers to searching using the root of a word to allow variants of the word to be detected. For example, a search of "onychomycosis and controlled clinical trial" will detect fewer studies than a search for "onychomycosis and control*" (where "control*" contains a wild card that will allow detection of all words that begin with the root "control"). Truncation can be performed on textword and MeSH heading searches.

To increase the specificity of searches, selecting specific subheadings of MeSH terms and limiting the search may be helpful. MeSH heading terms can be limited to specific subheadings to help narrow search results to relevant articles. For example, onychomycosis has subheadings that restrict retrieved articles to ones dealing with diagnosis or drug treatment.2 Searches can be limited in many ways, including publication type, language, human subjects and date of publication. Restricting the publication type to randomised controlled trial or case-control study is a useful way to limit retrieved articles to those of highest quality.

Performing a sensitive or specific search from scratch is often a time-consuming task, and arriving at an efficient search strategy to suit one's particular needs is sometimes a work of art. Once accomplished, it is important to be able to edit, save and retrieve the search strategy. The saved strategy can then be used in future searches of different subjects without having to rethink or retype the whole search procedure. The methods for performing these techniques (textword and MeSH searching, exploding, truncation, using subheadings, limiting and saving) vary according to the platform used. Mastering them will greatly improve searching efficiency.

Specific search strategies - "filters" - have been developed to help find relevant references and exclude irrelevant references for best evidence about diagnosis, therapy, prognosis, harm and prevention.8 You can limit your results to systematic reviews using the following strategy:

1. subjects of interest (for example onychomycosis)

2. REVIEW-ACADEMIC (use LIMIT)

3. REVIEW-TUTORIAL (use LIMIT)

4. Systematic$ and (review$ or overview$) (textword)

The strategy to search the Medline database for evidence about diagnosis is to combine the subject or subjects with a combination of terms as follows:2**

1. Subject (for example onychomycosis) Terms to use for maximum sensitivity of the search:

2. sensitivity-and-specificity (MeSH) or

3. sensitivity (textword) or

4. diagnosis (subheading) or

5. diagnostic use (subheading) or

6. specificity (textword)

Terms to use for maximum specificity of the search:

**The terms used in the examples were specifically designed for use with OVID to search the Medline database. They may have to be modified for use with other searching platforms. The use of OVID is not an endorsement. It is an available platform with which the author has competence.

7. explode sensitivity-and-specificity (MeSH) or

8. (predictive and value*) (textword)

If in a hurry, the best one-term strategy:

9. sensitivity (textword)

For example, using OVID to search the Medline database, a specific search for tests to establish a diagnosis of onychomycosis would be [1 and (7 or 8)], a sensitive search [1 and (2 or 3 or 4 or 5 or 6)], and a quick search (1 and 9).

The strategy to search the Medline database for evidence about therapy is to combine the subject or subjects with a combination of terms as follows2:

Subjects:

1. disorder (for example onychomycosis)

2. treatment (for example terbinafine)

3. alternative treatment (for example itraconazole)

For maximum sensitivity:

4. randomised controlled trial (publication type, limit) or

5. drug trial (subheading) or

6. therapeutic use (subheading) or

7. random* (textword)

For maximum specificity:

8. double and blind* (textword) or

9. placebo* (textword)

Best one-term strategy:

10. clinical-trial (publication type, limit)

For example, using OVID, a specific search for therapy of onychomycosis with terbinafine or itraconazole would be [1 and (2 or 3) and (8 or 9)], a sensitive search [1 and (2 or 3) and (4 or 5 or 6 or 7)], and a quick search [1 and (2 or 3) and 10].

The suggested strategy to search the Medline database for evidence about harm is to combine the subject or subjects with a combination of terms as follows2:

Subjects:

1. medication (for example terbinafine)

2. alternative medication (for example itraconazole)

For maximum sensitivity:

3. explode cohort-studies (MeSH) or

4. explode risk (MeSH) or

5. odds and ratio* (textword) or

6. relative and risk (textword) or

7. case and control* (textword)

For maximum specificity:

8. case-control-studies (MeSH) or

9. cohort-studies (MeSH)

Best one-term strategy: 10. risk (textword)

For example, using OVID, a specific search for adverse effects of terbinafine or itraconazole would be [(1 or 2) and (8 or 9)], a sensitive search [(1 or 2) and (3 or 4 or 5 or 6 or 7)], and a quick search [(1 or 2) and 10]. High-quality case-control or cohort studies are not frequently found in the dermatological literature. Sensitive search strategies and scanning the long lists of articles retrieved are likely to yield the best evidence most efficiently.

These filters have been incorporated into the PubMed Clinical Search engine of the NLM and are available at http://www.ncbi.nlm.nih.gov/ PubMed/clinical.html.8 PubMed Clinical Search is the preferred method for searching the Medline database for best evidence. It can be freely used by anyone with internet access.1,2

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