Welcome to the section of the EBM Express course on Using Advanced Search Strategies in PubMed.  EBM Express is designed to build your understanding of evidence-based practice in short, manageable blocks of content.  

In this section, we will explore advanced search techniques and strategies to help you achieve the best results in PubMed. 

In previous modules, you have learned how to begin a search from the PubMed homepage. Now, we will start with the Advanced Search Screen. 

We will cover phrase searching, truncation, proximity searching, and field tag searching. Please note that using any of these techniques will turn off the Automatic term mapping feature in PubMed. Automatic term mapping means that the search terms you enter into the search box are automatically mapped to MeSH terms.  

To search for words as a phrase, put double quotation marks around them. Otherwise, the search engine defaults to using the AND operator between the search terms.   In this screenshot of a search history, the phrase "postoperative complications" yields nearly half as many results compared to searching without quotation marks, resulting in more relevant outcomes. 

In this screenshot of an abstract from a search conducted for the term postoperative complications without using quotes, the term "postoperative" appears several times, and   "complications" appears once, but they do not appear together.  

In this next screenshot of an abstract, searching postoperative complications surrounded by quotation marks, the results show the searched phrase. Postoperative complications appears as a phrase three times in the abstract and is also listed in the keywords section. 

To search multiple endings of a word, use an asterisk at the root of the word. The root must have at least 4 characters for this to work. For example, Injur asterisk will return injury, injuries, etc. You can also use truncation within a phrase. In this example, “child asterisk disease” will return child disease, child’s disease, childhood disease, children’s disease.  

Here is a screenshot of a search history, showing the results obtained by using truncation versus searching for each phrase separately.  Searching Child asterisk disease yields over 1,900 results, while searching for "children’s disease," "child’s disease," and "child disease" each returns results in the 200s, and "childhood disease" returns just over 1,000 results. Using truncation in this case captures all of these phrases and more 

Proximity searching is another useful technique. It allows you to specify the number of words between your search terms. This method is broader than phrase searching but narrower than using the AND operator, which is the default if you do not use quotation marks around your search terms. You can use proximity when searching in the title, title/abstract, or affiliation fields. The format for proximity searching is your search terms in quotes, followed by an opening bracket, the field, a colon, a tilde, the number of words that can be between the search terms, and a closing bracket.   

Here is a screenshot showing a citation and a partial abstract from the search results for the phrase "sleep therapy" in the Title/Abstract field. In this search, "N" (or the number of words allowed between the search terms) is set to 3. This means that there can be up to 3 words separating "sleep" and "therapy." Also, note that the words can be in any order, as shown in this abstract, which includes phrases such as "therapy on sleep," "therapy on self-reported sleep," and "therapy improves sleep." 

The last technique we will explore is field tag searching. This method allows you to limit your search term to a specific field, such as title, title/abstract, Medical Subject Heading, author, or journal name.  

There are two ways to apply this technique. The first is to add the field abbreviation in brackets after your search term. For example, adding  ‘tiab' in brackets after 'heart failure'   ensures that 'heart failure' is found in the title and abstract. Changing the field abbreviation to ‘majr’ means that heart failure must be a major Medical Subject Heading.  

The second method for using field searching involves the Advanced Search Builder on the Advanced Search page. In this method, use the dropdown menu in the fields box to choose a specific field before entering your search term in the Search Builder box. Then, select "ADD" on the right to add it to the query box.  

 

Now that we have covered advanced search techniques, let’s look at some helpful search tips. 

Tip number 1: Avoid stop words. Stop words are words that the database ignores during a search. These include the words 'for', 'of', 'in', 'among', and others.  If your search contains a stop word, the database will skip over it and continue with the next word. 

For example, in the search query  'depression among physicians’, the word ‘among’ is a stop word. As a result, PubMed ignores it and processes the search as "depression AND physicians."  

Tip number 2 -  Instead of applying the humans filter after conducting your search, you can achieve better results by incorporating the following at the end of your search string: NOT space opening parenthesis animals opening bracket MeSH terms closing bracket space NOT space humans opening bracket MeSH Terms closing bracket closing parenthesis. The Not-Not logic may seem counterintuitive, but it is effective. Using NOT-NOT excludes any studies that contain the undesired MeSH terms in the first NOT phrase  (in this case, animal-based studies), while still retrieving records that have the terms from the 2nd NOT phrase - humans. It also keeps records with NO MeSH terms. While this method may not eliminate all non-human studies, it does significantly reduce their numbers.  

The final tip is to apply filters, such as publication date and article type, after retrieving your search results. If you are affiliated with an institution, you do not need to use the full text or free full-text filter, as your institution can obtain articles that it does not own via interlibrary loan. If you do not see a specific filter you want on the filter sidebar, select 'Additional Filters' at the bottom of the filter list. There, you can choose language, age, sex, and more. Remember, your filters do not reset automatically when you start a new search; you must manually clear them. 

By using these techniques, strategies, and tips, you can create effective searches that retrieve precise and relevant results.