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Lack consistency in usage, definition, and sometimes spelling (e.g. GERD vs. GORD).
Either single words or phrases.
Used to search for matching words or phrases anywhere in the article records the database contains (such as title, abstract, journal title).
Used when no appropriate subject heading exists as an equivalent.
Sometimes either too broad or too narrow, resulting in either too many or too few results.
Reflective of recent phenomena in advance of when subject headings might be developed.
Medical Subject Headings (MeSH) are:
Pre-defined “controlled” vocabulary words used to describe the content in a database.
Consistent in their definition across the records in the database.
Less flexible and must be chosen from the thesaurus used by the database.
Only searched for in the subject heading field of the article record.
Helpful for retrieving a set of articles with fewer irrelevant results.
Slow to change--this means that the most recent changes in knowledge--on diseases, drugs, devices, procedures, concepts--may not be reflected in the controlled vocabulary.
Automatic Term Mapping
When you do a basic keyword search, PubMed returns articles with those terms, but also automatically maps your search terms to the MeSH that are used to index articles. The search results include the keywords and the MeSH term(s). This is one way to find relevant MeSH. You can also explore the MeSH database directly https://www.ncbi.nlm.nih.gov/mesh.
Which should I use?
The simple answer to the question of whether you should use keywords or subject headings is: it depends. Some basic guidelines are:
If the term or topic is very recent, keywords may be the best option.
If no Subject Heading exists for your term, or seems inadequate, use a keyword.
If the keyword is too vague or broad, a Subject Heading may help focus your search and eliminate too many results o e.g. neuroses would be a very broad keyword search
If you want a very comprehensive literature search, you should use both a keyword AND a subject heading o e.g. “heart attack” OR myocardial infarction[mesh]
You wouldn't want to rush into the big game without a plan, or hike into the woods without a compass and map, right?
It's easy to get lost in the amount of information that can be found in databases. You may pick out the perfect keywords only to find little to no results related to your topic. Does that mean the information you need isn't out there? Not necessarily!
Think about your research question, the scope of your investigation, and the keywords you may have begun generating for your topic.
In order to find and use information, you may need to take a step back and think about what you've already identified.
Ask yourself some of the following questions:
Is this the right search engine or database? Can I find the information I need here?
What keywords am I using? Is there another way to talk about what I'm trying to find? Do the people talking about this topic use different terms or phrases than I'm using?
Could I use controlled language or subject terms? What types of labels has the database assigned to similar sources?
What other requirements am I looking for and how can I narrow my results? Does it need to be scholarly or peer-reviewed? Does this information need to be a recent as possible?
You can also modify your results using various search strategies. The default of search engines and most databases is to separate keywords and search for them separately.
This quick, 3-minute video explains how to develop keywords. Thinking strategically about your research question and the terms can help you navigate the vast amount of resources more quickly.
The Power of And, Or, & Not
In a library database, you can control your results by connecting keywords with AND, OR, NOT, and by using other search strategies like putting "quotation marks" around phrases to keep them together in the search.
Use AND to narrow your results. Your results must include each term.
Use OR to broaden your results. Your results could include any one of the terms.
Use NOT to exclude terms from your results.
Quotationmarks narrow your results by keeping words in a phrase together.
We can often do research without really thinking about it. But how do we know if our research strategy is the best or most efficient? What if we can't remember what's worked well or what hasn't in the past?
Using a Research Log to Document Your Search
A research log is a document that helps you keep track of and think about how you search for sources. A research log can be as informal as jotting down keywords and notes informally, or it can be more structured like writing annotations or summaries of sources and how they might fit into your project.
Materials from the Information Literacy Toolkit by Meg Meiman, which adapted materials from Maria Accardi & Tessa Withorn's Canvas module Access & Use.
Hierarchy of Evidence
While searching for research, it may be tricky to distinguish one study from another. The graphic above illustrates the hierarchy of evidence synthesis or different types of research papers. Here's a quick blurb about each:
Systematic Review Is an article that collects all possible studies related to a given topic and design, and reviews and analyzes the results. This is a time consuming method of analyzing research, which means there might not be a systematic review for your topic; however, if you do find a systematic review, it's a wonderful way to identify multiple articles on a singular topic.
Meta-Analysis Differs from a systematic review in that it uses statistical methods on estimates from two or more different studies to summarize the results of the studies. Meta-analyses can be helpful when seeking precise estimates of the effects of health care or particular intervention.
Randomized Controlled Trials RCT's include a randomized group of patients in an experimental group and a control group. These groups are followed up for the variables/outcomes of interest.
Case-Control Study Involves identifying patients who have the outcome of interest (cases) and control patients without the same outcome, and looking to see if they had the exposure of interest.
Cohort Study Identifies two groups (cohorts) of patients, one which did receive the exposure of interest, and one which did not, and following these cohorts forward for the outcome of interest.
Cross-Sectional Studies Observational studies that analyze data from a population at a single point in time. They are often used to measure the prevalence of health outcomes, understand determinants of health, and describe features of a population.
Case Series & Expert Opinion Case series is a group of case reports involving patients who were given similar treatment. Case reports and case series usually contain demographic information about the patient(s), such as age, gender, etc. Case series are uncontrolled. Expert opinions can include information from committee reports or other "voices of authority"; these types of resources are at the bottom of the hierarchy because both case series and expert opinions can be biased by the author's experience or opinions and there is no control of confounding factors.