A team surveys 1,200 students about sleep, social media use and grades. Paper one links sleep to grades. Paper two links social media to grades. Paper three links social media to sleep. Same sample, same questionnaire, near-identical methods sections, and none of the three mentions the other two. Each paper is technically correct, but together they are a textbook case of salami slicing.
Pressure to publish makes “how many papers should one study become?” a very practical question. The answer is not “always one.” It depends on whether each paper answers a distinct question and whether the shared material is disclosed openly.
Three terms that get mixed up
| Term | What it is | Telltale sign |
|---|---|---|
| Duplicate publication | The same data and results published twice | Two papers with near-identical results tables |
| Redundant or overlapping publication | Substantial overlap in data and conclusions, not disclosed | Methods and some results repeated with no citation of the earlier paper |
| Salami slicing | Dividing one study into minimal units to multiply output | One variable per paper, same sample, questions that cannot stand alone |
All three cause the same harm: they make one finding look as though several independent studies confirmed it. In a meta-analysis, a sample counted twice distorts the pooled estimate, and reviewers often cannot tell.
When several papers from one study are legitimate
Large projects, especially longitudinal cohorts and multi-site trials, almost always produce several papers. That is fine when all four conditions hold:
- Each paper answers a different question, not the same question with a different outcome variable swapped in.
- Each paper stands on its own: a reader of that paper alone can understand and evaluate it.
- Papers cross-cite: later papers state that the data come from the same project and cite earlier outputs.
- Editors are told: the cover letter mentions related papers published or under review and offers copies.
For the student survey, a healthier plan would be one main paper testing the three-variable model, and a second paper only if there is a genuinely different question, say, a comparison between first-year and final-year students that was planned from the start, citing the first paper throughout.
Republishing in another language
Researchers often publish first in a national-language journal and later want to reach an international audience. Translating the paper and submitting it as new work is duplicate publication, even though similarity software will not catch it across languages. A translated republication is legitimate only when:
- Both journals agree (the original publisher often holds copyright).
- The translation states on its first page that it is a translation or secondary publication and cites the original.
- The content is faithful to the original and does not add new data presented as new findings.
ICMJE guidance on secondary publication follows exactly this logic. In practice, many international journals decline translations, so the more realistic route is to extend the work with new data and a new question and cite the earlier paper as prior work.
Conference papers, theses and preprints
- Conference abstracts: almost every journal accepts full papers developed from them. Mention it in your cover letter.
- Full papers in peer-reviewed proceedings: a grey zone. Some fields treat them as formal publications; a journal version usually needs substantial extension and disclosure. Read the target journal’s policy.
- Theses and dissertations: most journals do not treat a thesis in a university repository as prior publication, but say so anyway.
- Preprints: widely accepted, though policies still vary in some fields. Check before posting.
Reusing methods text: where people worry too much
When the same protocol underpins several papers, rewording the methods just to dodge a similarity score can make the description less accurate. Many guidelines accept reuse of standard methods text if the earlier paper is cited. A tidy approach is a brief summary plus “the full protocol is described in [earlier paper].” What you must not reuse is the results or the discussion.
A self-check before submitting the second paper
Answer these five questions honestly:
- If I merged this paper into the earlier one, would readers lose anything? If not, this is a slice.
- Does any table or figure here closely resemble one in the earlier paper?
- Have I cited the earlier paper and stated that the sample is shared?
- Does my cover letter list every related paper?
- If a meta-analyst read both papers, could they accidentally count my sample twice?
If an overlap has already happened
Duplicate publication is often spotted when a reviewer recognises a familiar table or when a systematic reviewer finds two papers reporting the same participants. Common outcomes are a notice of duplicate publication or retraction of the later paper. If you notice first, write to the editor of the later paper, explain what happened and propose a notice linking the two. Early self-reporting always leads to a gentler outcome.
Something to do this week: list your publications, group them by dataset, and check that each paper cites the others from the same project. For future projects, agree a simple publication plan when data collection starts, naming the questions that will become separate papers, so that nobody has to decide under deadline pressure.
Câu hỏi thường gặp
Is it wrong to publish two papers from one study?
Not necessarily. If each paper answers a different question, stands on its own and cites the other, that is a legitimate use of the data. The problem is splitting purely to increase output while hiding the connection.
Can I republish my paper in English if it was published in another language?
Only with the agreement of both journals and if the translation is clearly labelled as a secondary publication citing the original. Submitting a translation as new work is duplicate publication.
What is salami slicing in research?
It means dividing one study into the smallest publishable units to maximise the number of papers. It makes a finding look independently replicated and can bias meta-analyses.
Is reusing my own methods section self-plagiarism?
Many journals accept reuse of standard methods text when the earlier paper is cited. A short summary with a reference to the original protocol is the safest approach.
Can a conference paper be submitted to a journal?
Conference abstracts are routinely developed into journal articles. Full papers in peer-reviewed proceedings usually need substantial extension and disclosure, depending on the journal’s policy.
