There are several reasons to search for existing reviews on your topic. Consider:
"environmental health" is in quotation marks because it's searching for these two words together in this order. Leaving out the quotation marks will bring up search results for "environmental" and "health" separately as well as together. [tiab] means that this search is only looking in the title or abstract fields in PubMed. The terms cancer* and neoplasm* are truncated--the asterisk looks for these exact words plus any alternate endings, e.g., cancer, cancers, cancerous, neoplasm, neoplasms.
On the left-hand side of the page, there is a section called "Article Type" and a link at the bottom of that section that says "See all article type filters". Clicking this link brings up all articles types and allows for selecting Meta-Analysis, Scoping Review, and Systematic Review at the same time, which was done for this search.
This is a very specific search. It's good for finding existing reviews on your topic, but you typically do NOT want to use checkbox limiters when you are constructing your comprehensive search for your evidence synthesis project, and you would also use more search terms. Refer to the "Step 2: Searching" tab in this guide for more information.
Here is a visual of what the above PubMed search looks like in the search box.
As with all research projects, you don't want your evidence synthesis topic to be too broad or too narrow. A popular tool for framing research questions in health and medicine is PICO, an acronym that stands for patient/population, intervention, comparison, and outcome. While this is useful for reviews of intervention studies, it's not the best framing tool for review topics that would focus on other study designs, such as observational studies, interview or survey research, and so forth. The table below from Munn et al. (2018) describes some other framing tools for evidence synthesis topics with example research questions for each.
| Review Type | Aim | Question | Example |
| Effectiveness | To evaluate the effectiveness of a certain treatment/practice in terms of its impact on outcomes | Population, Intervention, Comparator/s, Outcomes (PICO) [23] | What is the effectiveness of exercise for treating depression in adults compared to no treatment or a comparison treatment? [69] |
| Experiential (Qualitative) | To investigate the experience or meaningfulness of a particular phenomenon |
Population, Phenomena of Interest, Context (PICo) [13] | What is the experience of undergoing high technology medical imaging (such as Magnetic Resonance Imaging) in adult patients in high income countries? [70] |
| Costs/Economic Evaluation | To determine the costs associated with a particular approach/treatment strategy, particularly in terms of cost effectiveness or benefit | Population, Intervention, Comparator/s, Outcomes, Context (PICOC) [14] | What is the cost effectiveness of self-monitoring of blood glucose in type 2 diabetes mellitus in high income countries? [71] |
| Prevalence and/or Incidence | To determine the prevalence and/or incidence of a certain condition | Condition, Context, Population (CoCoPop) [15] |
What is the prevalence/incidence of claustrophobia and claustrophobic reactions in adult patients undergoing MRI? [72] |
| Diagnostic Test Accuracy | To determine how well a diagnostic test works in terms of its sensitivity and specificity for a particular diagnosis | Population, Index Test, Reference Test, Diagnosis of Interest (PIRD) [16] |
What is the diagnostic test accuracy of nutritional tools (such as the Malnutrition Screening Tool) compared to the Patient Generated Subjective Global Assessment amongst patients with colorectal cancer to identify undernutrition? [73] |
| Etiology and/or Risk | To determine the association between particular exposures/risk factors and outcomes |
Population, Exposure, Outcome (PEO) [17] |
Are adults exposed to radon at risk for developing lung cancer? [74] |
| Expert opinion/policy | To review and synthesize current expert opinion, text or policy on a certain phenomena | Population, Intervention or Phenomena of Interest, Context (PICo) [18] | What are the policy strategies to reduce maternal mortality in pregnant and birthing women in Cambodia, Thailand, Malaysia and Sri Lanka? [75] |
| Psychometric | To evaluate the psychometric properties of a certain test, normally to determine how the reliability and validity of a particular test or assessment. | Construct of interest or the name of the measurement instrument(s), Population, Type of measurement instrument, Measurement properties [31, 32] | What is the reliability, validity, responsiveness and interpretability of methods (manual muscle testing, isokinetic dynamometry, hand held dynamometry) to assess muscle strength in adults? [76] |
| Prognostic | To determine the overall prognosis for a condition, the link between specific prognostic factors and an outcome and/or prognostic/prediction models and prognostic tests. | Population, Prognostic Factors (or models of interest), Outcome (PFO) [20, 34–36] | In adults with low back pain, what is the association between individual recovery expectations and disability outcomes? [77] |
| Methodology | To examine and investigate current research methods and potentially their impact on research quality. | Types of Studies, Types of Data, Types of Methods, Outcomes [39] (SDMO) | What is the effect of masked (blind) peer review for quantitative studies in terms of the study quality as reported in published reports? (question modified from Jefferson 2007) [40] |
Think of a protocol as a road map for your review. It helps you plan where you're going and keep everyone on track. A protocol also helps avoid "scope creep" by clearly defining your topic early. "Scope creep" refers to expanding your topic after you begin searching for literature and piecing together your review. This can lead to your review becoming large and unwieldy with elements that may not clearly relate to each other. It's important to refine your topic in the early exploratory stage before you write your protocol. Revising your topic later will require rewriting and re-registering the protocol if you have it published in a protocol registry.
Registering a protocol has several benefits, such as increasing transparency, reducing the risk of bias, and preventing duplicate reviews (Moher et al., 2015).
Moher, D., Shamseer, L., Clarke, M., Ghersi, D., Liberati, A., Petticrew, M., Shekelle, P., Stewart, L. A., & PRISMA-P Group. (2015). Preferred reporting items for systematic review and meta-analysis protocols (PRISMA-P) 2015 statement. Systematic Reviews, 4(1), 1-9. https://doi.org/10.1186/2046-4053-4-1
Protocol registries:
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