Sunday, August 13, 2006

What's Up With the "MeSH" Tags?

Today we're going to delve a bit into a spot where blogging and librarianship collide - subject assignment, or tagging. It's not a women's health thing, but will explain something I regularly do on this blog. You may have noticed that, at the end of each of my posts, there are two sets of tags: Technorati and MeSH. You may already be familiar with Technorati, which helps people find blog posts on a particular tag/topic, but probably wonder what the MeSH is all about. I've never really explained it or why I add them, but was prompted to by fellow medical librarian blogger David Rothman (who facilitated this great list of medical lib blogs).

What are MeSH Tags?
MeSH (pronounced just like "mesh"), or Medical Subject Headings, is the set of controlled vocabulary from the National Library of Medicine. According to the NLM, "It consists of sets of terms naming descriptors in a hierarchical structure that permits searching at various levels of specificity." In plain English, it's a set of terms that can be assigned to things to indicate what they are about and help you find things about the subject you want, not unlike Technorati tags, but it's used in medical applications. For example, the PubMed (or MEDLINE, for you sticklers) database indexes* articles from health-related academic journals, such as the Journal of the American Medical Association. When they add a record for an article from JAMA, they assign subject terms, so people searching for research on that subject can find the articles. Those terms are MeSH terms.
[*indexes=includes in the database and assigns info such as author, title, issue, subjects to help you search and find]

MeSH terms are set up in hierarchy, to help find specifically what you are looking for. It's a "tree," sort of like when you learned about the animal kingdom (Kingdom, Phylum, Class, Order, etc.). MeSH starts with 16 basic categories, like Anatomy, Organisms, and Diseases. If you're looking for breast cancer, though, you probably don't want to search for "Diseases," because you'll get every disease under the sun. The folks who assign the MeSH terms would navigate down the tree, from Diseases, to Neoplasms (cancers), to Neoplasms by Site, to Breast Neoplasms, so you can search for articles tagged as being about "Breast Neoplasms" and get much closer with your search to what you actually want to read and learn about. It's a way to make your search results better, and the search process less frustrating.

Now, librarians would refer to MeSH as a "controlled vocabulary" (loosely meaning there are specific terms meaning specific things that you have to choose from) rather than "tags," and the assignment of these subject terms as "indexing" rather than "tagging," but you and I can see the similarity, no?

So far, so good, right?

Why assign MeSH tags to blog posts?
The short and sweet answer is, "For the same reason as the Technorati tags - to help you find more stuff on whatever I'm talking about." The audience for this blog is largely "regular people" rather than medical librarians. In the beginning, I started adding MeSH terms to the bottom of the posts so those few medical librarian readers could see what MeSH terms are used to represent a topic and click on them for medical articles if they so desired. I began to realize that I was learning a ton of new MeSH terms that sped up my professional work by adding them to posts on this blog (because I already knew some of the right terms rather than having to look them up), so that was a second motivation to keep it up. Finally, transparency is a big motivator for providing them to my non-medical, non-librarian audience. Women's health topics are often controversial (abortion, emergency contraception, whether condoms reduce HPV transmission, etc.), and I obviously don't have time to read every single piece of research that is published on every topic I post about. However, if you click on one of the tags, you can easily find a list of articles on whatever subject I've posted on, read the research, and make up your own mind. Overall, I think assigning the tags makes me a better librarian, and allows the reader to explore a topic in more detail if he or she chooses to do so.

Why not construct PubMed searches that explicitly find articles on the topic (like HPV AND condoms), rather than separate terms (i.e. one for HPV, one for condoms)?
Because I was interested in displaying the specific individual terms rather than forcing the reader into my set of search results. Combine as needed.

What happens if I click on one of your MeSH tags?
If you click on one of the terms, you'll be taken to the PubMed database (the major medical research database), directly to a search on that term. That means you'll see a list of articles published in medical/nursing journals that are about that topic. For example, here's one on "Contraception, Postcoital" (emergency contraception).

Can I read the articles in the list?
Sometimes. Publishers (except the open access ones) obviously have an economic interest in selling subscriptions rather than giving everything away for free. However, PubMed has a set of icons to let you know just what is available. Beside each citation in the results list, you'll see what looks like a piece of paper. If it is beige with lines, you can read the abstract. If it has a green stripe, you should be able to read the full-text of the article for free (although this doesn't always work). If it has green and orange, the whole article is definitely available for free, via PubMed Central. If something particularly tickles your fancy but is not free online, try your local library, which may be able to get it for you via Interlibrary Loan.

How do you create the MeSH tags? (you should probably just skip to the next part if you're not a librarian or otherwise interested in this particular level of detail)
Unfortunately, I have to do this by hand. Here's how it works:

1) PubMed includes the MeSH Database, which lets you look for the right terms, tells you what they mean, and lets you select them to include in your search. It also lets you narrow down your search in certain ways, by applying subheadings (a way to focus in on things like prevention, drug therapy, etc.) I start there, and do a search for the concept. For example, I might search the MeSH Database for "abortion."

2) The MeSH database translates my term into what it thinks I might mean and gives me a list of choices for the right term. In the abortion example, I get a list of options such as "Abortion, Induced" and "Abortion, Spontaneous" and "Abortion, Criminal." Say I want abortion the way most people think of it, in the Planned Parenthood sense, then I want to choose "Abortion, Induced." I can tell that by reading the definition it gives me, "Intentional removal of a fetus from the uterus by any of a number of techniques."

3) Looking at the info for "Abortion, Induced," I can see a set of limits (the subheadings) to apply. If I want articles on the legal aspects of abortion, I would click on the "legislation and jurisprudence" box to limit my search to that. I'm also going to click on the "Restrict Search to Major Topic Headings Only" box, because I want articles that are primarily about legal/judicial aspects of abortion.

4) Click on the "Send to Search Box with AND" option in the Send To pull down menu. I'll see ""Abortion, Induced/legislation and jurisprudence"[MAJR]" in my search box, and then click on "Search PubMed" to run the search.

5) Whee, I have my search results! But I can't just copy the URL in the top of my browser (well, I could, but sometimes it doesn't work for more complex searches, so I'm in the habit). Nope - have to click on the "Details" tab, then the URL button, then I can copy/paste the URL from the browser.

6) Then I use that URL just like any other URL you would link, surrounding the MeSH term I've selected. So you see in my MeSH Tags: Abortion, Induced/legislation and jurisprudence. You click on that, you get search results on that topic, like "Increase in obstacles to abortion: the American perspective in 2004" and "Prenatal screening, autonomy and reasons: the relationship between the law of abortion and wrongful birth."

It sounds like a tediously long process, but it goes fairly quickly once you are used it and start to have many of the terms memorized.

Anything else?
Yes - in the interest of keeping the list of search results relatively short when you click on a tag, I limit the searches in certain ways. Sometimes that will mean limiting the search to English, and usually means "majoring" the term, which means I restrict the search to return articles where that subject term is part of the main focus of the article. You can always see exactly what I've done by looking at the search box or clicking on the "Details" tab.

Also, here are a ton of tutorials for learning how to search PubMed and use the MeSH Database.

Finally, I don't use my site statistics tool to keep track in any way of which MeSH tags people leave through, or who uses them to search for a topic. It's all about your privacy.

If you have any questions, please feel free to leave them in the comments or send me an email.

[Off-topic, Related, for David: My RSS feeds for keeping up with everything, sorely in need of additions.]

Technorati Tags: ; ; ; ; ;
MeSH Tags: Abstracting and Indexing; Librarians; Medical Subject Headings; MEDLINE; Vocabulary, Controlled


Blogger David Rothman said...

Rachel, this is awesome. Thanks so much for explaining to why and how so clearly.

There's got to be an easier way, though, for you to make these.

3:42 PM  
Blogger Rachel said...

Thanks. I agree that an easier way would be nice, I just haven't figured out how yet!

4:29 PM  
Blogger BeckyJ said...

Fantastic explanation of MeSH and its usefulness!

8:53 AM  

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