Breaking Down Differences Between a Systematic review and a Systematic Literature Review

For those not immersed in systematic reviews, understanding the difference between a systematic review and a systematic literature review can be confusing. It helps to realise that a “systematic review” is a clearly defined thing, but ambiguity creeps in around the phrase “systematic literature review” because people can and do use it in a variety of ways. 

A systematic review is a research study of research studies. To qualify as a systematic review, a review needs to adhere to standards of transparency and reproducibility. It will use explicit methods to identify, select, appraise, and synthesise empirical results from different but similar studies.

The study will be done in stages:

1. In stage one, the question, which must be answerable, is framed
2. Stage two is a comprehensive literature search to identify relevant studies
3. In stage three, the identified literature’s quality is scrutinised and decisions made on whether to include each article in the review
4. In stage four the evidence is summarised and, if the review includes a meta-analysis, the data extracted; in the final stage, findings are interpreted.

Some reviews also state what degree of confidence can be placed on that answer, using the GRADE scale. By going through these steps, a systematic review provides a broad evidence base on which to make decisions about medical interventions, regulatory policy, safety, or whatever question is analyzed. By documenting each step explicitly, the review is not only reproducible, but can be updated as more evidence on the question is generated.

Sometimes when people talk about a “systematic literature review”, they are using the phrase interchangeably with “systematic review”. However, people can also use the phrase systematic literature review to refer to a literature review that is done in a fairly systematic way, but without the full rigor of a systematic review. 

For instance, for a systematic review, reviewers would strive to locate relevant unpublished studies in grey literature and possibly by contacting researchers directly. Doing this is important for combatting publication bias, which is the tendency for studies with positive results to be published at a higher rate than studies with null results. It is easy to understand how this well-documented tendency can skew a review’s findings, but someone conducting a systematic literature review in the loose sense of the phrase might, for lack of resource or capacity, forgo that step.

Another difference might be in who is doing the research for the review. A systematic review is generally conducted by a team including an information professional for searches and a statistician for meta-analysis, along with subject experts. Team members independently evaluate the studies being considered for inclusion in the review and compare results, adjudicating any differences of opinion. In contrast, a systematic literature review might be conducted by one person.

Overall, while a systematic review must comply with set standards, you would expect any review called a systematic literature review to strive to be quite comprehensive. A systematic literature review would contrast with what is sometimes called a narrative or journalistic literature review, where the reviewer’s search strategy is not made explicit, and evidence may be cherry-picked to support an argument.

FSTA – Food Science and Technology Abstracts is a key tool for systematic reviews and systematic literature reviews in the sciences of food and health.

• A defining characteristic of a systematic literature review is its thoroughness. A systematic review must capture all the relevant literature on a question so that its conclusion is based on all available evidence. Because FSTA indexes research articles related to the science of food and health wherever they appear, including journals not indexed in PubMed, Web of Science, CAB Abstracts, or other databases, using FSTA will help ensure that literature searches are exhaustive.
• The patents indexed help find results of research not otherwise publicly available because it has been done for commercial purposes.
• The FSTA thesaurus will surface results that would be missed with keyword searching alone. Since the thesaurus is designed for the sciences of food and health, it is the most comprehensive for the field. 
• All indexing and abstracting in FSTA is in English, so you can do your searching in English yet pick up non-English language results, and get those results translated if they meet the criteria for inclusion in a systematic review.
• FSTA includes grey literature (conference proceedings) which can be difficult to find but is important to include in comprehensive searches.
• FSTA content has a deep archive. It goes back to 1969 for farm to fork research, and back to the late 1990s for food-related human nutrition literature — systematic reviews (and any literature review) should include not just the latest research but all relevant research on a question. 

You can also use FSTA to find literature reviews.

FSTA allows you to easily search for review articles (both narrative and systematic reviews) by using the subject heading or thesaurus term “REVIEWS" and an appropriate free-text keyword.

• On the EBSCO platform, an FSTA search for reviews about cassava would look like this: DE "REVIEWS" AND cassava.

In 2011 FSTA introduced the descriptor META-ANALYSIS, making it easy to search specifically for systematic reviews that include a meta-analysis published from that year onwards.

• On the EBSCO platform, an FSTA search for systematic reviews with meta-analyses about staphylococcus aureus would look like this: DE "META-ANALYSIS" AND staphylococcus aureus.

Systematic reviews with meta-analyses published before 2011 are included in the REVIEWS controlled vocabulary term in the thesaurus.

An easy way to locate pre-2011 systematic reviews with meta-analyses is to search the subject heading or thesaurus term "REVIEWS" AND meta-analysis as a free-text keyword AND another appropriate free-text keyword.

• On the EBSCO platform, the FSTA search would look like this: DE "REVIEWS" AND meta-analysis AND carbohydrate*

EBSCO offers FSTA – Food Science and Technology Abstracts on EBSCOhost® and EBSCO Discovery Service™. EBSCO, along with IFIS, recently sponsored the Research Information webinar, “Literature reviews in food science – what, why and how?”

This post was originally published by IFIS Publishing on the Thought for Food Blog.