 Whether you're looking for a few high-quality articles to answer a specific question, scoping the literature to see what's already been published on the topic of interest, or conducting a more in-depth literature review, you'll want to incorporate a variety of search techniques into your search strategy. In this lecture, we'll focus on the most common techniques and demonstrate how to use them in PubMed. Specifically, we'll focus on using the Boolean operators AND and OR to combine search terms, nesting to group similar terms, truncation to search for words with multiple endings, and quotes to search for phrases. While this lecture focuses on PubMed, the techniques that we're discussing work in most literature databases, such as M-Base, CINNL, PsychInfo, Web of Science, and Scopus. Let's use the following scenario to dive deeper into PubMed. Your colleagues published an article 15 years ago about the possible risk of mobile phones causing cancer in children. They are now interested in seeing how the literature has changed on this topic, given the increased use of smartphones throughout the world. The easiest method to search PubMed is to type in a few key terms into the search box at the top of the homepage. For example, we can type cancer, children, mobile phones, and click the search button. To see exactly what PubMed did to find these results, click on the advance link and scroll down to the history and search details box. Next, click on the arrow underneath the details heading. Here, you'll see the official search strategy that PubMed used. There's a lot going on here that we could discuss, but for right now, take a look at the ands and ors that PubMed has added to the search. And or and not are referred to as Boolean operators. You may have used them in searches that you've conducted in the past, but let's take a few minutes to review how they work in the database. Think about what happens when we combine terms with and. For example, if we were to type cancer and children and mobile phones into the search box, we are telling the database that we want articles that include both terms. Each time I and in a term, the results get smaller. So when I just search for articles pertaining to cancer, I find over 4 million results. When I type and children, the results drop down to around 300,000. This is because the articles now need to address both terms to show up in the results. If I and in mobile phones, the results drop down to about 186. When you combine terms with or rather than and such as mobile phones or smartphones or cell phones, you're telling the database to find articles on any of these topics. Each time I or in a term, the results get bigger. Searching for mobile phones yields around 14,000 results. Typing mobile phones or smartphones or cell phones finds 11,000 more results. For this reason or is most often used with synonyms or similar terms in order to expand a search. Not does just what you think it does. It tells the database to eliminate articles from the search that use a specific term. Typing cancer not leukemia will look for articles about cancer but removes any articles that talk about leukemia. It's tempting to use not to remove irrelevant citations. For example, I often get asked if it's all right to type not adults to find articles that focus on children. I usually respond with a word of caution. Not runs the risk of removing citations that could be relevant. For example, many articles about children may also mention adults somewhere in the abstract. We will miss out on those possibly valuable articles. Here are a couple technical things to keep in mind when using Boolean operators. PubMed recommends that they are entered in all caps. You may notice that the search works correctly if you use lowercase, but this is only a recent improvement that has been made to PubMed. To be certain that your search is working properly, always use Boolean operators in capital letters. Remember in the search details how PubMed automatically added the AND in between our search terms? By default, PubMed assumes that you're ANDing terms together unless you specifically use a different Boolean operator. This brings up an important point. While sometimes it feels like PubMed is reading your mind, in reality it's only searching according to how it's programmed. It's using an algorithm to conduct its searches. This point becomes important when you begin to use a mix of ANDs and ORs. If you type children AND cancer and mobile phones or smartphones or cell phones, you might be surprised by the results that you get. For example, this article, a new smartphone application to predict hematologic acute radiation syndrome based on blood cell count changes, the H-Model app. Logically, you're asking for articles about our mobile phone concept as it pertains to cancer and children. Take a minute to see how PubMed is searching with these terms. PubMed is programmed to read from left to right, so it's finding all of the articles on cancer and children and mobile phones or all of the articles on smartphones or all of the articles on cell phones, which explains some of the strange results. To fix this problem, you'll need to group your OR terms with parentheses. This action is called nesting, and if you remember nesting an algebra, it works in a similar way. In our search to ensure that PubMed is ANDing and ORing exactly as we intended, we place parentheses around mobile phones or smartphones or cell phones. Going back to that idea of how PubMed assumes you're ANDing together terms, this becomes a problem when you're searching with phrases. For example, let's say I want to expand my search to see if the proliferation of cell towers also increases the risk of cancer in children. When I search the phrase cell towers, I get off topic results like skin cell heterogeneity in development, wound healing, and cancer. Looking at the search details, we can see that PubMed is finding these results because it's splitting the terms apart and looking for articles that address both the word cell and the word towers. To remedy this problem, keep your terms together and put double quotation marks around phrases. Looking at our search, we can use quotes around the phrase mobile phones and cell phones. We don't need to use quotes around smartphones because this is all one word. You'll only need to use double quotes around multi-word phrases. To save you time, databases including PubMed allow you to search on variations of a root word by using the asterisk to represent the rest of the term. Using this asterisk is called truncation. For example, putting an asterisk at the end of mobile phone will retrieve mobile phone or mobile phones. Using an asterisk at the end of child will find variations of this root, so child, children, childhood, etc. As you can see, using truncation means that you don't need to think of all possible term variations and include them in your search. One important thing to note about truncation in PubMed, however, is that you can only truncate the last word of a phrase. So I can't search cell with an asterisk towers to get cell phone towers, even though it makes sense logically. Instead, I would have to type out each phrase and use an or. So cell tower with an asterisk or cell phone tower with an asterisk. In both cases, I put these phrases in double quotes. Notice in PubMed you can now use truncation and quotation marks to keep the phrases together. This is a new feature introduced in PubMed's latest upgrade. We started this lecture with a very simple search on the PubMed homepage. Now that we know about a few database search techniques, we can apply them to our search to make it more effective. First, I add in my similar terms placing an or in between them. I also make sure to group them together in parentheses. Then I put double quotes around the multi-word phrases. Last, I look for opportunities to use truncation. For example, I could search cancer and child with an asterisk and in parentheses mobile phone with truncation at the end of the E putting that phrase in double quotes or cell phone again truncation at the end of the E putting it in double quotes or smartphone with truncation at the end of the E or cell tower with truncation at the end of the R and putting that phrase in double quotes. In summary, using Boolean operators nesting phrase searching and truncation will put you on the right path for finding relevant results in PubMed. There are other search techniques that you can incorporate, but understanding how and when to use these four techniques is crucial to building an effective and efficient PubMed search.