# Is a Systematic Review Empirical Research? Clarifying the Distinction ## Quick Answer - A systematic review is a research method that collects and analyzes existing studies, but it does not generate new primary data, so it is not empirical research in the strict sense. - The practical distinction matters when you classify your study design, select reporting guidelines, and describe your methodology in grant applications and journal submissions. - The key limitation is that a systematic review depends entirely on the quality and availability of prior studies, so gaps in the literature limit what the review can conclude. ## Understanding the Core Distinction The confusion between systematic reviews and empirical research is common among graduate students, early-career researchers, and laboratory professionals who must classify their work for theses, journal submissions, and funding applications. The distinction is also semantic. It changes how you design your project, which reporting standards you follow, and how reviewers evaluate your contribution to the scientific literature. Empirical research, also called primary research, involves collecting new data through observation, experimentation, or direct measurement. A laboratory scientist measuring enzyme activity in tissue samples, a field ecologist counting bird populations, or a clinician recording patient responses to a treatment are all conducting empirical research. The defining feature is that the researcher directly interacts with the subject of study and generates original data that did not exist before the study began. A systematic review operates at a different level. It is a structured investigation of the existing research record. The researcher defines a focused question, searches systematically for all relevant studies, appraises the quality of those studies, and synthesizes their findings. The raw material for a systematic review is not new observations but the published and unpublished reports of other researchers' empirical work. The review produces new knowledge about what the evidence shows, but it does not produce new empirical data about the world. This epistemological difference matters for practical reasons. When you submit a manuscript describing a systematic review, editors and peer reviewers expect you to follow specific reporting guidelines designed for synthesis research. When you apply for funding, grant reviewers need to understand that your project will not generate primary data and therefore has different data management requirements. When you write your thesis methodology chapter, your committee will evaluate whether you have correctly positioned your work within the research design taxonomy. ## At a Glance | Feature | Empirical Research | Systematic Review | |---------|-------------------|-------------------| | Data source | Direct observation, measurement, or experimentation | Published and unpublished reports of prior studies | | Researcher role | Primary data collector | Evidence synthesizer and critical appraiser | | Output | New raw data and findings | Synthesized conclusions about the existing evidence | | Timeframe | Data collection occurs during the study period | Data collection is the literature search, which covers all time up to the search date | | Reporting guidance | Discipline-specific reporting standards for primary studies | PRISMA and other synthesis-specific reporting guidelines | | Replication | Another researcher can repeat the experiment or observation | Another researcher can repeat the search and selection process | The table above summarizes the practical differences that affect your daily research decisions. The most important distinction is the source of data. Empirical researchers create data. Systematic reviewers consume and interpret data that others have created. ## The Epistemological Basis of the Distinction The philosophical foundation of this distinction rests on what counts as evidence in scientific inquiry. Empirical evidence comes from direct sensory observation or measurement of phenomena. When a researcher records the weight of rats in a feeding trial, the resulting data point is empirical because it represents a direct measurement of a real biological system. A systematic review produces a different kind of knowledge. It produces knowledge about the state of the evidence. When a reviewer concludes that the literature supports a particular feeding strategy for dairy cattle, that conclusion is a synthesis of many individual empirical studies. The conclusion is evidence-based, but it is not itself empirical evidence about cattle. It is an interpretation of the empirical evidence that already exists. This distinction has a long history in the philosophy of science. Epistemologists distinguish between knowledge gained through direct experience and knowledge gained through reasoning about the reports of others. Both forms of knowledge are valuable in science, but they serve different functions and have different standards of validation. For practical purposes, the distinction affects how you answer the question, "What did you do for your research?" If you conducted an experiment, you can describe your materials, methods, and measurements. If you conducted a systematic review, you describe your search strategy, inclusion criteria, and synthesis methods. The two descriptions share some vocabulary, but the underlying activities are fundamentally different. ## How Systematic Reviews Use Empirical Evidence A systematic review is empirical in a limited sense. The review process itself involves systematic observation of the literature. The reviewer searches databases, screens titles and abstracts, extracts data from included studies, and records decisions. These activities are systematic and transparent, and they can be audited by other researchers. However, the object of observation in a systematic review is the research record, not the natural world. The reviewer observes what other researchers have reported, not the phenomena those researchers studied. This is a critical distinction. When a systematic reviewer extracts data from a study of antibiotic residues in milk, the reviewer is not measuring antibiotic residues. The reviewer is recording what the original researchers reported about their measurements. This is why systematic reviews are often described as secondary research. They are secondary because they analyze the products of primary research. The term secondary does not mean less important. It describes the relationship between the review and the underlying empirical studies. The practical implication is that a systematic review can be no more reliable than the studies it includes. If the primary studies have methodological flaws, the review will inherit those flaws. This is why systematic reviewers spend substantial effort appraising the quality of included studies and why they report the risk of bias in their syntheses. ## Reporting Guidelines and Transparency The distinction between empirical research and systematic review has direct consequences for how you report your work. Reporting guidelines are checklists that tell researchers what information to include in their manuscripts so that readers can understand and evaluate the methods. The [EQUATOR Network](https://www.equator-network.org/) maintains a comprehensive library of reporting guidelines for different study types. For empirical studies, the appropriate guideline depends on the study design. Randomized trials use CONSORT, observational studies use STROBE, and diagnostic accuracy studies use STARD. These guidelines ask for detailed descriptions of the study population, interventions, measurements, and statistical analyses. For systematic reviews, the relevant guideline is PRISMA, which stands for Preferred Reporting Items for Systematic Reviews and Meta-Analyses. PRISMA asks for a detailed description of the search strategy, inclusion and exclusion criteria, study selection process, risk of bias assessment, and synthesis methods. The guideline also requires a flow diagram showing how studies were identified, screened, and included. The [EQUATOR Network](https://www.equator-network.org/) provides tools to help researchers select the right reporting guideline for their study type. Using the correct guideline is not optional. Most journals require authors to submit a completed checklist with their manuscript, and peer reviewers use the checklist to evaluate whether the methods are fully reported. Choosing the wrong guideline signals to reviewers that you do not understand your own study design. If you submit a systematic review with a STROBE checklist, reviewers will question whether you understand the difference between primary and secondary research. This is a common reason for manuscript rejection or requests for major revision. ## The Role of Systematic Reviews in Grant Applications When you apply for research funding, the distinction between empirical and synthesis research affects how you describe your project and what reviewers expect from your proposal. The [National Institutes of Health](https://grants.nih.gov/) provides official guidance on grant applications, including how to describe research strategies and methods. Grant reviewers evaluate whether your proposed methods are appropriate for your research question. If you propose a systematic review, you must explain why a synthesis of existing evidence is the right approach. You must also describe your search strategy, your inclusion criteria, and your plans for quality appraisal and synthesis. One important consideration is that systematic reviews do not generate new data in the same way that empirical studies do. This affects the data management section of your application. The [NIH Data Management and Sharing Policy](https://sharing.nih.gov/data-management-and-sharing-policy) requires researchers to describe how they will manage and share data generated by their research. For a systematic review, the data are the extracted information from included studies, the search records, and the screening decisions. You must describe how you will preserve and share these materials so that other researchers can verify your work. Another consideration is the timeline. Empirical studies often require extended periods for data collection, especially if they involve animal subjects, clinical populations, or long-term observations. Systematic reviews have a different timeline. The literature search and screening can be completed in a defined period, but the process requires careful planning to ensure completeness and reproducibility. Grant reviewers also consider the expertise of the research team. A systematic review requires skills in database searching, study screening, quality appraisal, and evidence synthesis. These skills are different from the skills required for laboratory work or field research. Your application should demonstrate that your team has the appropriate expertise. ## Researcher Identity and Record Keeping The distinction between empirical and synthesis research also affects how you document your professional identity and maintain your research records. The [ORCID for Researchers](https://info.orcid.org/researchers) resource explains how researchers can maintain a persistent digital identifier that links to their publications and research activities. When you register your ORCID record, you can list your systematic reviews alongside your empirical studies. The record does not distinguish between the two types of research, but your publication list will show the mix of primary and secondary research you have conducted. This is useful for job applications, promotion reviews, and grant applications because it demonstrates your range of research skills. Maintaining accurate records of your systematic review process is essential for reproducibility and for responding to peer review. You should document your search strategies for each database, the dates of your searches, the number of records retrieved, the screening decisions, and the reasons for excluding studies. This documentation is the equivalent of a laboratory notebook for a systematic review. The [Committee on Publication Ethics](https://publicationethics.org/core-practices) core practices emphasize the importance of accurate record keeping and transparent reporting. These practices apply equally to empirical research and systematic reviews. Fabricating search results, omitting studies that do not support your conclusions, or failing to disclose conflicts of interest are ethical violations regardless of your research design. ## Practical Workflow for Conducting a Systematic Review If you decide that a systematic review is the appropriate approach for your research question, you should follow a structured workflow. The steps below describe the process from planning to publication. ### Step 1: Formulate a Focused Research Question Your research question must be specific enough to guide your search and your inclusion criteria. A vague question such as "What do we know about antibiotic use in livestock?" is too broad for a systematic review. A focused question such as "What is the effect of prophylactic antibiotic use on the incidence of respiratory disease in feedlot cattle?" is more appropriate. Use a structured framework to develop your question. For clinical and animal health questions, the PICO framework is common. PICO stands for Population, Intervention, Comparison, and Outcome. Defining each element helps you build your search strategy and your inclusion criteria. ### Step 2: Develop a Search Strategy Your search strategy must be comprehensive and reproducible. You will search multiple databases, and you must document the exact search terms and filters you use for each database. The search strategy should include controlled vocabulary such as MeSH terms in PubMed as well as free-text terms. The [National Library of Medicine](https://www.ncbi.nlm.nih.gov/books) provides access to authoritative biomedical books and research method references that can help you develop your search strategy. These resources explain how to build effective searches and how to document your process for reproducibility. ### Step 3: Screen Studies Against Inclusion Criteria You will screen the titles and abstracts of all records retrieved by your search. Studies that clearly do not meet your inclusion criteria are excluded at this stage. The full text of remaining studies is then reviewed to make the final inclusion decision. You should document the number of records screened, the number excluded, and the reasons for exclusion. This information is required for the PRISMA flow diagram. ### Step 4: Assess the Quality of Included Studies Quality appraisal is a critical step that distinguishes a systematic review from a simple literature review. You must evaluate the risk of bias in each included study using a validated tool appropriate for the study design. The results of your quality appraisal should be reported transparently. Readers need to know whether the evidence base is strong or weak and how the quality of the included studies affects your conclusions. ### Step 5: Synthesize the Findings Synthesis can be quantitative or qualitative. A meta-analysis is a statistical synthesis that combines the results of multiple studies to produce a pooled estimate. A narrative synthesis describes the findings of the included studies and explains patterns and inconsistencies. Not all systematic reviews include a meta-analysis. Meta-analysis is only appropriate when the included studies are sufficiently similar in their populations, interventions, and outcomes. If the studies are too heterogeneous, a narrative synthesis is more appropriate. ### Step 6: Report According to PRISMA Your final manuscript should follow the PRISMA reporting guideline. The [EQUATOR Network](https://www.equator-network.org/) provides access to the PRISMA checklist and explains how to use it. The checklist ensures that you report all essential elements of your review methods and findings. ## Records and Measurements for Systematic Reviews Systematic reviews require careful documentation of the review process. The table below lists the key records you should maintain and the measurements you should track. | Record Type | What to Document | Why It Matters | |-------------|------------------|----------------| | Search log | Database names, search dates, exact search strings, number of results | Reproducibility and transparency | | Screening log | Number of records screened, excluded, and included at each stage | Required for PRISMA flow diagram | | Inclusion and exclusion criteria | Explicit criteria applied to each study | Transparency and reproducibility | | Data extraction form | Standardized form for extracting data from included studies | Consistency and completeness | | Quality appraisal results | Risk of bias ratings for each included study | Transparency about evidence quality | | PRISMA checklist | Completed checklist submitted with manuscript | Journal compliance and reviewer evaluation | These records serve the same function as a laboratory notebook in empirical research. They allow other researchers to verify your process and to replicate your review if they wish. ## Common Failure Patterns in Systematic Reviews Understanding common failure patterns helps you avoid mistakes that lead to rejection or to unreliable conclusions. ### Inadequate Search Strategy A search that misses relevant studies produces a biased review. Common errors include searching only one database, using only free-text terms without controlled vocabulary, and failing to search gray literature such as conference abstracts and government reports. Your search strategy should be developed with the help of a librarian or information specialist if possible. ### Lack of Duplicate Screening Screening decisions should be made by at least two reviewers working independently. If one person screens all studies, errors are more likely to pass through. Disagreements between reviewers should be resolved through discussion or by a third reviewer. ### Failure to Assess Quality A systematic review that does not assess the quality of included studies is not a systematic review. It is a narrative literature review. Quality appraisal is essential because it tells readers how much confidence they should place in the findings. ### Inappropriate Meta-Analysis Combining studies that are too different produces a meaningless pooled estimate. Meta-analysis requires clinical and statistical homogeneity. If the studies are too heterogeneous, you should present a narrative synthesis instead. ### Selective Reporting Omitting studies that do not support your preferred conclusion is a form of bias. Your inclusion criteria must be applied consistently, and you must report all studies that meet your criteria, regardless of their findings. ## Limitations of Systematic Reviews Systematic reviews have important limitations that you should acknowledge in your work and consider when interpreting findings. The most fundamental limitation is that a systematic review depends on the existing literature. If no studies have addressed your question, your review will find nothing to synthesize. This is a valid finding, but it means the review cannot answer the question. Publication bias is another limitation. Studies with positive findings are more likely to be published than studies with null or negative findings. If your review only includes published studies, your conclusions may overstate the evidence for an effect. The quality of the included studies limits the quality of the review. If the primary studies have serious methodological flaws, your synthesis will inherit those flaws. Your quality appraisal should make this limitation explicit. Finally, systematic reviews are time-consuming and require specialized skills. A well-conducted review can take months or years to complete. The effort is justified when the review addresses an important question and when the existing evidence is sufficient to support synthesis. ## Welfare and Safety Context The distinction between systematic reviews and empirical research has particular relevance in animal science and veterinary medicine. Systematic reviews are often used to evaluate the evidence for animal welfare interventions, disease prevention strategies, and production practices. A systematic review of animal welfare research synthesizes the findings of empirical studies that measured outcomes such as stress indicators, behavior, health, and productivity. The review can identify gaps in the evidence base and guide future research priorities. It can also inform decisions about which interventions are supported by sufficient evidence to justify implementation. The [National Library of Medicine](https://www.ncbi.nlm.nih.gov/books) provides access to resources on research methods that are relevant to animal health and welfare research. These resources can help you design a systematic review that addresses animal welfare questions rigorously. When you conduct a systematic review in the animal science field, you should consider the welfare implications of your findings. If the evidence supports a particular intervention, your review may influence decisions that affect animal welfare. Your conclusions should be based on the evidence and should acknowledge uncertainty where it exists. ## Professional Escalation Criteria You should seek professional guidance when you encounter situations that exceed your expertise or when the stakes of your review are high. Consult a librarian or information specialist when you are developing your search strategy. A professional searcher can help you identify all relevant databases, build effective search strings, and document your searches for reproducibility. This is especially important for complex topics that span multiple disciplines. Consult a statistician when you are considering a meta-analysis. A statistician can help you determine whether meta-analysis is appropriate, select the correct effect measure, and interpret the results. Statistical errors in meta-analysis are common and can lead to incorrect conclusions. Consult a subject matter expert when you are appraising the quality of included studies. An expert can help you understand the methodological nuances of the studies in your field and can identify flaws that a generalist might miss. Escalate to your institution's research integrity office if you suspect that any of the studies you are reviewing involve research misconduct. The [Committee on Publication Ethics](https://publicationethics.org/core-practices) core practices describe the responsibilities of researchers and institutions in addressing misconduct. If you identify concerns about the integrity of a study you are reviewing, you should report your concerns through the appropriate channels. ## Frequently Asked Questions ### Is a systematic review considered primary research? No. A systematic review is secondary research because it analyzes the findings of primary studies instead of generating new data through direct observation or experimentation. The reviewer synthesizes existing evidence but does not collect new empirical data. ### Can a systematic review include unpublished studies? Yes. A well-conducted systematic review searches for unpublished studies, including conference abstracts, dissertations, and reports in the gray literature. Including unpublished studies helps reduce publication bias, but these studies may not have undergone peer review, so their quality must be assessed carefully. ### What is the difference between a systematic review and a literature review? A systematic review follows a structured, transparent, and reproducible process for searching, selecting, and appraising studies. A narrative literature review is less structured and may not document its search methods. Systematic reviews are designed to minimize bias, while narrative reviews are more subjective. ### Do I need ethics approval for a systematic review? Ethics approval is generally not required for systematic reviews because the research does not involve human or animal subjects directly. However, you should check your institution's policies and the requirements of the journal where you plan to publish. Some institutions require registration of systematic review protocols. ### How long does a systematic review take to complete? A systematic review typically takes several months to more than a year, depending on the scope of the question, the volume of literature, and the size of the review team. The search, screening, and data extraction phases are time-intensive and require careful planning. ### Can a systematic review be part of a thesis or dissertation? Yes. Many graduate programs accept systematic reviews as thesis or dissertation projects. You should check your program's requirements and discuss your plans with your advisor. Some programs require that a systematic review be accompanied by a component of primary research. ### What is a meta-analysis and is it the same as a systematic review? A meta-analysis is a statistical technique for combining the results of multiple studies. A systematic review may include a meta-analysis, but not all systematic reviews do. Meta-analysis is only appropriate when the included studies are sufficiently similar to justify combining their results. ### How do I choose the right reporting guideline for my systematic review? The [EQUATOR Network](https://www.equator-network.org/) provides a searchable library of reporting guidelines. For systematic reviews, the PRISMA guideline is the standard. You should also check the instructions for authors of your target journal to confirm which guideline they require. ## Related Articles - [Ethical Considerations in Psychological Research: A Guide for Students and Early-Career Researchers](/blog/guides/ethical-considerations-in-psychological-research-a-guide-for-students-and-early-career-researche) - [Meta-Analysis vs Systematic Review: What's the Difference?](/blog/guides/meta-analysis-vs-systematic-review-what-s-the-difference) - [Open Science Practices: A Guide for Researchers](/blog/guides/open-science-practices-a-guide-for-researchers) - [Epidemiological Study Designs: An Overview for Researchers](/blog/guides/epidemiological-study-designs-an-overview-for-researchers) - [Longitudinal Research Designs: An Overview for Life Scientists](/blog/guides/longitudinal-research-designs-an-overview-for-life-scientists) ## References and Further Reading - [Research Methods Resources](https://www.ncbi.nlm.nih.gov/books). National Library of Medicine. - [EQUATOR Network](https://www.equator-network.org/). EQUATOR Network. - [Core Practices](https://publicationethics.org/core-practices). Committee on Publication Ethics. - [NIH Grants and Funding](https://grants.nih.gov/). National Institutes of Health. - [ORCID for Researchers](https://info.orcid.org/researchers). ORCID. - [Data Management and Sharing Policy](https://sharing.nih.gov/data-management-and-sharing-policy). National Institutes of Health. - [NCBI Literature Resources](https://www.ncbi.nlm.nih.gov/). National Center for Biotechnology Information. - [PubMed](https://pubmed.ncbi.nlm.nih.gov/). National Library of Medicine. > This article is educational and does not replace institutional policy, professional advice, or applicable safety and regulatory requirements.