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CancerGuide: Researching Your Options

Finding Information
Steve's Medline Tips
Understanding What You Find
Steve's Medline Tips

A few very basic tips on searching MedLine... the first thing of course is to play with it and experiment! You'll probably get more out of these tips after you spend a little time actually searching MedLine.

There are several different MedLine accesses (See my main Medline article) and they each have a different way of searching the database. At the same time, the basic concepts are always the same. This article doesn't assume any particular access method so to apply these tips you need to look for the way to do the things I discuss in the help for whatever access you're using.

Search Terms

Each reference is indexed under a variety of terms. You search for references on a subject by asking for the references indexed under terms related to that subject.

Words in the title, and even words in the abstract are indexed. The problem with looking for literal words is that there are usually lots of synonyms and variations for any word. Some search algorithms allow you to type only the first part of the word, to give you all words that start with that part in common, or allow you to use wild card characters. This is helpful, but there is a better solution.

Medline includes a set of concept terms called MeSH terms. MeSH stands for Medical Subject Heading. It is almost always better to use a Medical Subject Heading rather than a title or abstract word, because all papers having to do with that subject will be indexed under that one term. The National Library of Medicine has a book of all the MeSH terms, but friendly versions of MedLine, like PaperChase and PubMed, will actually guide you towards the correct MeSH term given a title word.

Using Search Results to Find MeSH Terms

When I search on a term I'm not sure is right, or if I have combined a number of terms and am not sure the result is right, I like to examine the first few references in the list to see if I'm getting what I want. When I look up something that I know should be common, I expect to see a lot of references. If I don't, I know I'm probably using the wrong term. If I don't know the MeSH term for the topic I'm interested in, I often look up a word that I know just has to be Be in the title of some papers on that subject. Then the system may guide me to a MeSH term automatically, or I can look at a few of the references and see what MeSH terms they are indexed under (there is always a way to get a list of the MeSH terms a particular reference is index under). From this, I can usually pick the right MeSH term. Finally, when I have a list that is not too big, and seems to have the right stuff, I'll scan through it selecting only the interesting ones to download.

Search by Author

You can also look up papers by author. This can be very helpful in tracking down a report mentioned in the media where they usually give the name of the researcher, but no citation to the paper, although the delay before a reference gets into the database can get in the way of that. More commonly, if you find one interesting paper, you may want to use this feature to look up other papers by the same authors.

If you are interested in papers written by Smith you know you're going to have trouble because there are sure to be lots of Smiths in the database. First, you can usually include the author's first and middle initials in the search term. I tend to avoid using a middle initial because I've found it's common for some papers to include Authors' middle names and others not. Even using Smith J as the name is likely to bring up papers from lots of different authors. Other tactics I use are to use the less common name from the list of authors on a paper and especially to look for papers by the Author that ALSO concern the subject of interest. Yang is a common name. Jim Yang is a prominent researcher in kidney cancer. Searching for Yang or even Yang J won't do, but searching for Yang J AND carcinoma, renal cell, works nicely.

Too Many References

If you look up all of the references on something like breast cancer, or colon cancer, you will get a list of tens of thousands of references, far more than you can look through in any reasonable amount of time. If you have a specific topic, such as a particular drug like Navelbine, you can look for all of the references that include the cancer of interest and Navelbine. This will be a much smaller list. Different MedLine search interfaces have different ways of allowing you to do this, but they all amount to the same thing.

Note that broad concepts like "treatment" and "prognosis" may not be MeSH terms, and searches based on these terms may incorrectly exclude many references because these terms don't happen to appear in the title. There is a way to handle these broad concepts in MedLine. MedLine has a relatively short list of concepts like "Treatment" or "Diagnosis" that can be used to "qualify" many MeSH terms. Qualifying terms are not separate MeSH terms, but rather can be used to modify MeSH terms and limit their scope. When you use a qualifier, only those references that also concern the qualifying term are included. Qualifiers are given two letter abbreviations such as "DT" for "Drug Treatment," and "AE" for "Adverse Effects". So if you qualify your list of 30,000 references on colon cancer with the DT qualifying term, you'll get only those references on drug treatment for colon cancer. MedLine search interfaces can give you a list or menu of qualifiers on request - it's worth it to take some time with the online help to learn how to do this.

I realize that the difference between adding a qualifier and doing an "and" with another term may be confusing. MeSH terms are very specific and there are lots of them. In contrast, qualifiers are broad concepts and there are only a few of them. In general, except for these qualifying terms, you have to look for very specific topics when you search.

There are some other ways of limiting the number of references. You can limit by date of publication and it often makes sense to limit to the last two or five years. You can also limit to review articles, which summarize the current state of knowledge on a specific topic. Looking for review articles is extremely useful when you're trying to get an initial overview. MedLine also lets you can limit to articles on humans, thus eliminating animal studies. You can also limit to articles that have abstracts online, and a number of other ways.

Too Few References

First, an unqualified search on any common disease or well known drug should yield thousands of references. If it doesn't, you immediately know something is wrong. Even if you specialize the search by looking only at a specific well known drug or treatment for your type of cancer, there will usually be dozens to hundreds of references. In general I try to find the right MeSH terms using the search results I have the way I described above. I also check spelling of all my terms and the syntax of my search. If I am combining several terms, I may try eliminating one or more to see if I get more results.

If I am looking for information on a rare cancer or a new experimental treatment there may really not be many references on it. It's always worth checking to make sure you have the best search terms as above. For new drugs, I will usually try to use both MedLine and Google to see if there are any other names for the same drug, by searching on the name I know and looking to see if the articles or abstracts I find also use any other names. I will also check the list of MeSH terms for any references I do find to see if there is a substance identifier (which is like a MeSH term) for the drug I am researching.



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This CancerGuide Page By Steve Dunn. © Steve Dunn
Page Created: August 9, 2004, Last Updated: August 9, 2004