Structure of Search Strategies for Systematic Reviews: Line by Line versus Block by Block versus Single-Line
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Over the past 18 years, I have had this discussion several times with information specialists, researchers, students, and colleagues. Some seem to be defending a single approach at the beginning of the conversation, but as we go forward, they change their minds.
Unsurprisingly, all three approaches of structuring the search strategies are useful at the right time and place. There is no advice in PRESS, PRISMA, MECIR, or PRISMA-S to push you to follow one of the approaches.
Since there is no best practice guide, many get confused about what structure to choose for each purpose. Before I start explaining and avoiding wasting your time, this post is not about structuring the search based on PICO families (PECO, PIPOH, PICOS, etc.).
Line by Line Search Strategy
Borrowed from computer programming, we put the single term in each line in this structure, and there is no guide on how much information you can put in each line. Since each line is concise — usually one term or one set of terms followed by field tags — the entirety of the structure becomes long, and you have to scroll from top to down to see all the lines. In some cases, there are 300–400 lines! At the same time, since each line carries only a little information, it is easy to follow each line and line numbers to figure out the structure by looking at Boolean logic such as AND, OR, and NOT. Line by line searching makes it very easy to find the errors. The main trouble is that if you want to run this search, you have to copy the line, paste it into the search box, and press Enter/Search 300–400 times, depending on the number of lines. If this repetitive task does not turn you into a mad hatter, it will waste time. On the other hand, it is easy to check and peer-review such strategies and shows the contribution of each term/line to the search, so it can be beneficial when you develop/validate a search filter. I use this structure for training purposes as students get it well and find the errors on the spot. See a single example from Ovid Embase below:
1 exp Black Person/
5 “Women of Colo?r”.ti,ab.
7 Maternal Health Service/
8 exp Pregnancy/
10 Pregnancy Outcome/
11 Perinatal Care/
12 Pregnancy Complication/
13 Pregnant Woman/
24 Health Disparity/
25 Health Care Disparity/
28 Social Discrimination/
29 Health Equity/
30 Social Justice/
32 “Racial Prejudice”.ti,ab.
41 exp United States/
42 (United States).ti,ab,ad,gc,go,in.
47 6 and 23 and 40 and 46
Block by Block Search Strategy
In this type of structuring, you have one line per search concept. If you break your question into PICOS — or any other framework — elements, you will have 5 lines: P (population/ problem), I (intervention), C (comparator or control), O (outcome-rarely included in the search), and S (study design). The last line will combine all lines with AND to give you the final results.
In the following example, you only have to copy and paste 5 times, and you can see the search structure, which reflects the research question. It can be read easily, and you won’t need lots of scrolling unless you really have to run pages of terms. This structure is understandable to those who are not searching experts, and the structure helps you test combining 2, 3, 4, or 5 and mix and match the blocks to see what number of results is more reasonable. It must be noted that it may not be possible to break down searches into CLEAN single-concept blocks in complex searches and some blocks may have sub-blocks and sub-sub-blocks.
1 exp Black Person/ or (Black* or African* or Multiethnic* or “Women of Colo?r”).ti,ab.
2 Maternal Health Service/ or exp Pregnancy/ or Prematurity/ or Pregnancy Outcome/ or Perinatal Care/ or Pregnancy Complication/ or Pregnant Woman/ or (Pregnan* or Birth* or Post?natal or Gestation* or Peri?natal or Post?partum or Matern* or Ante?natal or Pre?natal).ti,ab.
3 Health Disparity/ or Health Care Disparity/ or Racism/ or Prejudice/ or Social Discrimination/ or Health Equity/ or Social Justice/ or (Racis* or “Racial Prejudice” or Discrimination or Disparit* or Inequit* or Inequalit* or Equalit* or Equity or Bias*).ti,ab.
4 exp United States/ or (United States or USA or “U.S.” or “U.S.A.”).ti,ab,ad,gc,go,in.
5 1 and 2 and 3 and 4
Single Line Search Strategy
It is possible to combine all the concepts and terms in a single line. This way, you only need to copy, paste, and press Enter only once rather than several or hundreds of times; for this why all the searches that I ran when I worked as a clinical librarian in the emergency department were in the single line structure. It may take the system some time to digest your search query, but a good system will finally give you the results while drinking your coffee/tea/water. In some cases, the system may give you error(s), which will not be easy to find in a large search. Since you do not have many lines, the search does not take much space and does not require scrolling down. If you are busy or lazy, this may work just fine.
(exp Black Person/ or (Black* or African* or Multiethnic* or “Women of Colo?r”).ti,ab.) and (Maternal Health Service/ or exp Pregnancy/ or Prematurity/ or Pregnancy Outcome/ or Perinatal Care/ or Pregnancy Complication/ or Pregnant Woman/ or (Pregnan* or Birth* or Post?natal or Gestation* or Peri?natal or Post?partum or Matern* or Ante?natal or Pre?natal).ti,ab.) and (Health Disparity/ or Health Care Disparity/ or Racism/ or Prejudice/ or Social Discrimination/ or Health Equity/ or Social Justice/ or (Racis* or “Racial Prejudice” or Discrimination or Disparit* or Inequit* or Inequalit* or Equalit* or Equity or Bias*).ti,ab.) and (exp United States/ or (United States or USA or “U.S.” or “U.S.A.”).ti,ab,ad,gc,go,in.)
Since it may seem a dull collection of words, I use formatting — such as Bold, Underline, and Italic — and colour-coding [see top image] to separate the blocks for the audience.
The structure of the search strategy depends on the purpose of the presentation of the search strategy, your or your customers’ preferences, the complexity of the search, and the database’s search capabilities.
I must confess not all the search interfaces allow you to use all three structures. Oddly, sometimes they may allow you to run a single line search, but the next time the search interface may stop you with an unknown error or break down/parse your query differently than the intended way. Assuming that you have all three options, I summarise the pros and cons in the following table, which is not complete, but I am happy to add more if you share:
Remember: in complex searches, we may have to use a combination of these three structures.
On 9th June 2021, I updated the entry to include input from a Twitter conversation. Special thanks to the contributors.
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Cite as: Shokraneh, Farhad. Structure of Search Strategies for Systematic Reviews: Line by Line versus Block by Block versus Single-Line. Medium 6 June 2021; [Revised 9 June 2021]. Available from: https://farhadinfo.medium.com/structure-of-search-strategies-for-systematic-reviews-line-by-line-versus-block-by-block-versus-d59aae9e92df