STATISTICAL METHOD
Synthesis Without Meta-Analysis
Statistical Consulting for Structured Synthesis
We plan and report synthesis without meta-analysis when pooling is not appropriate, specifying how studies are grouped, the standardized metric, the synthesis method and the certainty of evidence, so the conclusions remain transparent.
No Commitment Required
Strictly Confidential
In-House PhD-Level Statisticians
Fixed Project Fee
Same-Day Response
METHOD OVERVIEW
What Is Synthesis Without Meta-Analysis?
Synthesis without meta-analysis is a structured way to combine quantitative evidence in a systematic review when studies cannot or should not be pooled into one summary estimate, for example because their effect measures, outcomes or designs differ too much. SWiM is reporting guidance, not a statistical model: it asks reviewers to state how studies were grouped, which standardized metric and synthesis method were used, and how certainty was judged. Methods include medians and ranges of effects and effect direction plots, and vote counting by statistical significance is discouraged. OnlineSPSS, a specialist statistical consultancy for academic, clinical and professional research, provides this analysis within your review design, with the relevant checks, effect summaries, interpretation and publication-ready reporting.
WHEN TO ENGAGE
When Is a Structured Synthesis Appropriate?
This approach fits a review whose studies cannot be pooled, and these are the situations in which researchers most often ask us to plan, run or confirm it.
Outcomes Too Varied to Pool Studies measure the outcome on scales, time points or definitions that cannot share one metric, so a single meta-analytic estimate would mislead.
Incomplete Effect Reporting Many studies omit standard errors or report only direction or significance, so effects cannot be pooled and a structured synthesis is needed for what they give.
Prespecified Synthesis Plan The protocol must state how studies will be grouped and compared if pooling fails, so the synthesis is not an unstructured narrative written after the results.
Reviewing a Completed Synthesis A narrative synthesis was written and a reviewer asked how studies were grouped. Independent Statistical Review rechecks the grouping rules and the basis for each conclusion.
ANALYTICAL APPROACH
How We Plan a Structured Synthesis
Within the family of Evidence Synthesis & Meta-Research, a synthesis without pooling is built from explicit groupings, metrics and methods, not from narrative alone.
Grouping and Standardized Metric Studies are grouped by population, intervention and outcome per the protocol, and effects are put on one standardized metric so that direction and size can be compared.
Synthesis Method Choice We choose a transparent method, such as medians and ranges of effects, an effect direction plot or a harvest plot, and we state why pooling was not appropriate.
Result Selection and Variation We set rules in advance for which result each study contributes, and examine whether effects vary by population or risk of bias, without vote counting by significance.
Certainty and Reporting We rate certainty with GRADE and report against the nine SWiM items, including the limits of the synthesis, so readers see the strength of evidence, not only its direction.
DELIVERABLES
What You Receive
As part of our Meta-Analysis & Evidence Synthesis service, the synthesis is delivered with the summaries, checks and files needed to report and defend it.
Data & Variable Review Effect data, outcome definitions, scales, time points and the direction of benefit are aligned, and each study's usable metric is documented before any grouping.
Method-Specific Checks Groupings are checked against the protocol and tested for sensitivity, with risk of bias and study size carried through to every table, plot and conclusion.
Statistical Results Standardized effects per study with intervals where reported, group-level medians and ranges, and the direction and consistency of effects across studies.
Publication-Ready Tables & Figures Effect direction plots, harvest plots or structured tables with study size and risk of bias, formatted to the SWiM items, PRISMA 2020 or the journal's requirements.
Interpretation The synthesis is written as direction, size and consistency of effect with its limits, the reason for not pooling, and the certainty of evidence in the GRADE framework.
Reproducible Analysis Files R scripts, Stata do-files or SPSS syntax are provided with the extraction sheet, so each table and plot can be rebuilt when studies are added or data are corrected.
ALTERNATIVE METHODS
When Another Method May Be More Appropriate
We choose the method by the question and by what the studies report. Pooling is sometimes possible after all, and these methods fit those situations.
01
Meta-Analysis
When studies share a comparable effect measure and population, pooling gives a summary estimate with its uncertainty and is preferable to a descriptive synthesis.
02
Meta-Regression
Once enough studies share a metric for pooling, differences in effect by population or program can be modeled formally instead of described group by group.
03
Systematic Review
When the need is the review itself, from protocol and search to screening and risk of bias, that process comes first, and SWiM covers only how results are synthesized.
04
Individual Participant Data (IPD) Meta-Analysis
When reporting is the obstacle, participant records can be reanalyzed on a common metric with consistent definitions, which may make pooling possible.
CASE EXAMPLE
How We Work in Practice
An illustration of how a synthesis without pooling moves from a written plan to a transparent, reportable summary of the evidence.
ILLUSTRATIVE EXAMPLE · WORKPLACE HEALTH EVIDENCE REVIEW · UNITED STATES
A government evidence unit reviewed workplace physical activity programs and sickness absence for a policy brief, but studies reported absence in days, episodes and proportions.
The protocol, written before screening, stated that pooling would be attempted only for studies sharing a metric, and that otherwise a structured synthesis would follow the SWiM items. Absence was reported in incompatible forms, and several studies gave only direction and a p-value. Following the protocol, studies were grouped by program type, and we expressed each effect as relative change in absence where the data allowed. Counting significant studies was set aside because it ignores size and precision. Medians and ranges of effects per group and an effect direction plot, showing study size and risk of bias, carried the synthesis, and certainty was rated with GRADE.
Outcome: The unit received the grouped synthesis tables, the effect direction plot, the stated reason for not pooling, the GRADE certainty ratings, a completed SWiM checklist and the scripts.
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 Structured Synthesis
Standardized metrics, summary tables and effect direction plots are prepared in R, Stata, IBM SPSS and Python, with syntax or scripts provided where applicable.
RESEARCH DISCIPLINES
Structured Synthesis Across Research Fields
Synthesis without pooling is used wherever evidence is too varied for one summary estimate, each field with its own designs, outcomes 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 an evidence synthesis researcher who wanted a second set of statistical eyes on a review before reporting it.
“I wanted a second set of statistical eyes on our SWiM (Synthesis Without Meta-Analysis), mainly because of whether the studies were comparable enough to pool and how heterogeneity should be handled. The review was practical and specific, and the final results were much easier to explain to the rest of the research team. The final output was concise, clearly interpreted, and ready to use in our research reporting.”
RESEARCH RESPONSIBILITY
Statistical Support Without Taking Over Your Research
We provide the statistical work for your structured synthesis, and the review, its meaning and its authorship stay entirely with you.
Agreed Statistical Support We provide the agreed methodological, analytical and statistical reporting support for your structured synthesis, 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, the grouping rationale and the 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 Synthesis Without Pooling
Short answers to what researchers ask before synthesizing studies without pooling, from SWiM and vote counting to confidentiality and the assessment process.
Is SWiM a statistical method or reporting guidance?
SWiM is reporting guidance, not a statistical model. Its nine items ask reviewers to state how studies were grouped, which standardized metric and synthesis method were used, how heterogeneity was examined and how certainty was assessed. The statistical content comes from the synthesis methods chosen, such as medians and ranges or effect direction plots, which we select to fit your data.
Can I just count the studies with significant results?
Vote counting by statistical significance is discouraged. It discards the magnitude and precision of each effect, treats a small underpowered study like a large one and can point the wrong way. Counting by direction of effect is less flawed, but it still ignores size, so we pair direction with effect sizes where available, study size and risk of bias.
When is it acceptable not to perform a meta-analysis?
When the studies cannot answer one question together: populations, interventions or outcomes differ, effects or variances cannot be extracted, or heterogeneity is so great that a summary would mislead. Having few studies is not by itself a reason, since a meta-analysis of two comparable studies can be valid. The protocol states the reason, and the report explains it.
Can you review an analysis that has already been completed?
Yes, we can review a completed synthesis before submission or a response to reviewers. We check the grouping, the metric and the synthesis method against the SWiM items, whether vote counting by significance crept in, the certainty ratings and the reporting, and confirm what stands or needs to change.
How do you protect my dataset and research confidentiality?
Your extraction sheets, output files 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
Synthesis Without Meta-Analysis?
Share your review question, the extracted study data and your protocol. We assess how the studies can be synthesized 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