STATISTICAL METHOD
Systematic Review Methodology
Statistical Consulting for Evidence Reviews
We apply systematic review methodology to your review question, from a protocol fixed in advance and duplicate screening and extraction to risk-of-bias appraisal and PRISMA 2020 reporting, with a meta-analysis only where the included studies justify one.
No Commitment Required
Strictly Confidential
In-House PhD-Level Statisticians
Fixed Project Fee
Same-Day Response
METHOD OVERVIEW
What Is a Systematic Review?
A systematic review answers a defined research question by identifying, selecting, appraising and synthesizing all eligible studies with explicit, prespecified methods designed to limit bias. It is defined by its process: a protocol registered in advance, a comprehensive and reproducible search, screening and data extraction by two reviewers, a risk-of-bias assessment of every included study and a synthesis planned before results are seen. A meta-analysis is one possible synthesis within a systematic review, not a requirement of it. OnlineSPSS, a specialist statistical consultancy for academic, clinical and professional research, provides systematic review methodology support within your review question, with the relevant checks, effect estimates, uncertainty measures, interpretation and publication-ready reporting.
WHEN TO ENGAGE
When Is a Systematic Review Appropriate?
A systematic review fits a question that a body of studies can answer, and these are the research situations in which researchers most often ask us to plan, support or confirm one.
Planning a Review From the Start A research team has a focused question but no registered protocol yet, and the review must be planned before the first search is run.
Screening Decisions in Dispute Two reviewers differ on whether a study is eligible or on an extracted value, and the team needs a resolution that will stand up to peer review.
Pooling Decision After Appraisal Included studies differ in design and outcomes, and the plan must say when a meta-analysis is justified and when a structured synthesis is used instead.
Reviewing a Completed Review A review is drafted or submitted, and an editor has questioned the appraisal or synthesis. Independent Statistical Review re-examines the synthesis and its statistics.
ANALYTICAL APPROACH
How We Support a Systematic Review
Within the family of Evidence Synthesis & Meta-Research, systematic review methods fix the design first, and the synthesis follows from what the included studies report.
Protocol and Eligibility We work with you on eligibility criteria, outcomes and the synthesis plan, which you register before screening. Criteria are worded so that two reviewers would apply them alike.
Screening and Extraction Records are deduplicated, two reviewers screen and extract independently on a piloted form, and each disagreement is settled by a written rule, never a silent override.
Bias Appraisal by Design Tools match the design, such as RoB 2 for randomized trials and ROBINS-I for non-randomized studies, and the judgments inform the synthesis instead of only being tabulated.
Synthesis and Reporting The planned synthesis is run, pooling only comparable studies, and certainty is rated per outcome. A PRISMA systematic review reports results for every included study, pooled or not.
DELIVERABLES
What You Receive
As part of our Meta-Analysis & Evidence Synthesis service, the review is delivered with the checks, syntheses and files needed to report and defend it.
Data & Variable Review Study screening and extraction records are reviewed for completeness, duplicates and consistent coding of study characteristics and outcomes.
Method-Specific Checks Reviewer agreement, risk-of-bias judgments and the comparability of included studies are examined, with sensitivity analyses where pooling is planned.
Statistical Results Study characteristics, risk-of-bias summaries and, where justified, pooled estimates with 95% confidence intervals and heterogeneity, or a structured synthesis.
Publication-Ready Tables & Figures A PRISMA 2020 flow diagram, study and risk-of-bias tables and forest plots, formatted to the reporting guidance and the journal's requirements.
Interpretation Findings are written for the evidence they support, with certainty considered in the GRADE framework and the limits of the search, studies and synthesis stated plainly.
Reproducible Analysis Files Extraction sheets, R scripts or Stata do-files and figure code are provided where applicable, so reported values can be traced and the review updated.
ALTERNATIVE METHODS
When Another Method May Be More Appropriate
We choose the method by the question the review must answer. A systematic review is a process, and these methods fit questions that call for a specific synthesis.
01
Meta-Analysis
When the included studies are comparable and share an effect measure, pooling them gives a summary estimate, as one synthesis option within the review.
02
SWiM (Synthesis Without Meta-Analysis)
If included studies cannot be pooled, a structured synthesis explains why, groups them as the protocol specified and avoids vote counting by statistical significance.
03
Network Meta-Analysis (NMA)
If the question asks which of several treatments works best and few were tested head to head, a network can use indirect evidence, under assumptions we examine.
04
Diagnostic Test Accuracy Meta-Analysis
When the studies evaluate a test against a reference standard, sensitivity and specificity are pooled jointly with a bivariate model, reported in line with PRISMA-DTA.
CASE EXAMPLE
How We Work in Practice
An illustration of how a review moves from a registered plan to a transparent synthesis that a panel can rely on.
ILLUSTRATIVE EXAMPLE · CLINICAL GUIDELINE DEVELOPMENT · UNITED STATES
A guideline group at a professional society was running a systematic review of delirium prevention in older surgical patients and needed a synthesis plan its panel could defend.
The protocol, registered before screening, set the eligibility criteria and fixed that trials sharing one delirium instrument would be pooled as risk ratios in a random-effects meta-analysis, and the rest synthesized without pooling. Two reviewers disagreed on whether quasi-randomized trials were eligible, so the resolution was documented and applied to every record, not trial by trial. Trials were appraised with RoB 2. Because several used different instruments and follow-up windows, only trials sharing an instrument were pooled, as planned, and the others were grouped by a stated rule.
Outcome: The group received the synthesis plan, the PRISMA 2020 flow diagram, risk-of-bias tables, pooled risk ratios with 95% confidence intervals, a structured synthesis for the other trials and the analysis files.
This example does not describe a real client or project. We never share details of actual client work, in line with the confidentiality we promise every researcher. This illustrative example is included to show the type, scope, and standard of work involved in this kind of analysis.
SOFTWARE
Statistical Software for Evidence Reviews
Review data are synthesized in R, Stata and IBM SPSS, and NVivo supports coding of narrative findings from included studies, with scripts provided where applicable.
RESEARCH DISCIPLINES
Systematic Reviews Across Research Fields
Systematic reviews are written in every field with a body of studies to weigh, each with its own study designs, appraisal tools and reporting conventions.
A Defined Process for Your Analysis
We review your dataset, research question and design before any work begins, so the scope, deliverables, timeline and fixed project fee are clear from the outset.
01
Share Your Research Materials
Send your dataset, research question, study design and any existing analysis plan or output. We will let you know if anything else is needed to assess the project.
02
Receive Your Assessment
Your statistically trained Research Coordinator reviews the project and confirms the required analysis, deliverables, timeline and fixed project price before work begins.
03
Analysis & Delivery
Once you confirm the scope, an in-house statistician completes the agreed analysis and delivers the outputs, interpretation and reporting files.
RESEARCHER VOICE
What Researchers Say
Feedback from a clinical epidemiologist who needed the comparability of studies and the reporting choices of a review worked through.
“We came to the team with a fairly technical Systematic Review problem: whether the studies were comparable enough to pool and how heterogeneity should be handled. They worked through the assumptions and reporting choices with us, then delivered a clean analytical summary rather than pages of software output. The final reporting was much easier to use in the manuscript and in responding to reviewer comments.”
RESEARCH RESPONSIBILITY
Statistical Support Without Taking Over Your Research
We provide the statistical work for your review, and the question, the search and the authorship stay entirely with you.
Agreed Statistical Support We provide the agreed methodological, analytical and statistical reporting support for your systematic review, within the scope confirmed before work begins.
No Intellectual Contribution OnlineSPSS claims no intellectual contribution to your research. Our work is statistical support, and authorship remains yours.
Your Research Decisions The review question, search, eligibility judgments and conclusions remain with you, and our statistical interpretation stays within what the included studies support.
Confidential Handling Research data and project details are handled confidentially and are not published. An NDA is available where required, and can be arranged before sensitive materials are shared.
FREQUENTLY ASKED QUESTIONS
Questions About Systematic Reviews
Short answers to what researchers ask before planning a review, from meta-analysis and registration to confidentiality and the assessment process.
Does a systematic review always need a meta-analysis?
No. What makes a review systematic is its prespecified protocol, comprehensive search and structured appraisal of each study, and a pooled estimate is only one possible result. Whether pooling happens depends on clinical and methodological comparability. A review whose studies cannot be combined is still a valid systematic review when it says so and reports why.
Why should the protocol be registered before screening?
Registration fixes the question, eligibility criteria, outcomes and synthesis plan before the results are known, so the review cannot be steered by what the studies show. Changes remain possible, but they are reported as amendments with reasons. A registry such as PROSPERO also makes duplicated reviews visible. Registering afterward cannot repair criteria that followed the findings.
Does following PRISMA 2020 make a review high quality?
No. PRISMA 2020 is a reporting guideline, a checklist and flow diagram for describing what was done, not an instrument that rates the review or its studies. Study quality is judged with risk-of-bias tools such as RoB 2 for randomized trials and ROBINS-I for non-randomized studies, and a review’s own conduct with a tool such as AMSTAR 2.
Can you review an analysis that has already been completed?
Yes, we can review a completed systematic review before submission or a response to reviewers. We check whether the protocol and the report agree, how screening and extraction disagreements were resolved, the risk-of-bias judgments, the synthesis choice and the PRISMA reporting, and confirm what stands or needs to change.
How do you protect my dataset and research confidentiality?
Your screening records, extraction sheets and any protocol or analysis plan are handled confidentially, and project information is not published. An NDA is available where required and can be arranged before sensitive materials are shared. Read more about confidentiality and data security.
What happens when I request an assessment, and how long does it take?
You share your research question, design and relevant materials, and a statistically trained Research Coordinator reviews the request and responds the same day. The analysis, deliverables, timeline and one fixed project fee are then confirmed before any work begins, so the timeline follows from the agreed scope.
Still have a question? Find more answers in our full FAQ.
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Need Support With a
Systematic Review?
Share your review question, protocol and any extracted data. We assess which parts of the review need statistical support and confirm the approach before any work begins.
No Commitment Required
Strictly Confidential
Fixed Project Fee
In-House PhD-Level Statisticians
Same-Day Response
Serving Researchers Since 2014