Second reviewer services for your systematic review

The case for a second reviewer is empirical, not ceremonial. Methodological research on study selection has repeatedly shown that a single screener misses eligible studies, and that adding an independent second reviewer recovers a meaningful share of them at both screening stages. Because a wrongly excluded study simply disappears from the review, the error can never be detected afterwards, which is why dual independent screening is written into the Cochrane Handbook and why PRISMA 2020 asks authors to state how many reviewers worked at each stage. Our guide to how many reviewers screening requires sets out the standard in detail.

The people this lands on hardest are solo doctoral candidates and small teams. A supervisor signs off the proposal, the work begins alone, and months later an examiner, an ethics panel, or a journal reviewer asks who the second reviewer was. At that point the choice is to recruit a colleague with no time, to downgrade the claim to a less rigorous review type, or to bring in an independent professional. We exist for that third option: a methodologist who joins your review, follows your eligibility criteria, and leaves behind the documentation that makes the dual process demonstrable.

The sequence below covers the full dual-review cycle. You commission the stages you need; some clients want blind screening only, others want the complete set through to risk-of-bias reconciliation.

1. 1

   Calibrate on your criteria

   We pilot your eligibility criteria on a sample of records with you, resolving interpretation differences before formal screening, so agreement statistics reflect real judgement rather than misunderstanding.

2. 2

   Blind title and abstract screening

   We screen the full deduplicated yield without sight of your decisions, in Rayyan, Covidence, or your platform of choice, keeping any record that could plausibly qualify.

3. 3

   Blind full-text screening

   We read every surviving full text against the criteria and record a specific exclusion reason for each paper we would reject, still blind to your calls until reconciliation.

4. 4

   Duplicate extraction and independent appraisal

   We extract data from the included studies onto your form in duplicate and score risk of bias independently with your chosen tool, ready for comparison against your assessments.

5. 5

   Reconcile, resolve, and document

   Decisions are unblinded and compared, conflicts are resolved against the criteria with an agreed tie-break route, and every resolution is logged alongside the agreement statistics.

The value of dual review depends entirely on the second set of decisions being made separately. We therefore screen blind: your inclusion and exclusion calls are hidden from us until both passes are complete, so our decisions cannot drift towards yours. The same discipline applies at full-text screening, where we record our own exclusion reasons before seeing yours, and at extraction, where the two forms are completed independently and then compared cell by cell. Where we disagree with you, we say so and show our reasoning against the criteria, because a second reviewer who simply confirms everything adds no protection and would not survive a probing question in a viva or peer review.

Disagreement is expected and useful. Most conflicts resolve quickly once the pair discusses how a criterion applies to the record in question, and persistent conflicts go to the tie-break route you nominate, typically your supervisor or a senior member of your team. Our guide to resolving screening conflicts explains the process we follow and the log we keep.

Every stage we double is quantified. We calculate Cohen’s kappa on the double-screened records and report it alongside raw percentage agreement, because kappa alone can mislead when eligible records are rare. You can check the arithmetic yourself with our kappa calculator for screening agreement, and our guide to inter-rater reliability in screening covers how to present the figure in your methods section. A weak value is treated as a signal to clarify the criteria and rescreen the affected records, not a number to bury, and the final write-up states plainly how agreement was measured, what it was, and how conflicts were settled. That paragraph, with the conflict log behind it, is what turns “two people looked at this” into a defensible documented agreement process.

You choose how our contribution appears, and we support either route. Some clients name our reviewer as a co-author, which is appropriate where the contribution meets the authorship standards of the target journal, and has the advantage that the methods section can name who performed each stage. Others prefer an acknowledged contributor credit, with the methods describing an independent second reviewer and the acknowledgements naming the contribution. Either way, the description is accurate: the review remains yours, the decisions are reconciled with you, and nothing in the paper claims more or less than what was done.

• An independent, blind screening decision on every record at both stages
• A full-text exclusion log with our specific reason for every rejected paper
• Duplicate data extraction reconciled against yours, cell by cell
• Independent risk-of-bias scores with justifications for every judgement
• Cohen's kappa and raw agreement figures, with a documented conflict-resolution log
• A methods-section paragraph describing the dual-review process, ready to use

This service is deliberately different from our complete screening service, where we run the whole screening stage with two of our own reviewers. Here, you are the first reviewer and we are the second, independent set of eyes on your review. The table shows where the two part.

We quote a fixed fee shaped by the size of the deduplicated yield, how many records reach full text, how many studies proceed to duplicate extraction and independent risk-of-bias assessment, and which stages you want doubled. If your review sits inside a thesis, our dissertation systematic review support page covers how this fits the wider project. Send your eligibility criteria and your search export, tell us which stages need a second reviewer, and we will return a fixed quote with no obligation to proceed.