Compare the DOI, title, authors, and year across both entries, then confirm whether either record is a preprint or a correction before you merge, because those differences change whether the two entries should be combined at all. A DOI lookup returns the metadata deposited for that DOI, so it gives you a fixed identifier to compare against the other entry rather than relying on how the title happens to be formatted.
1. Compare the DOI first. Open each entry and read the DOI field. If both entries carry the same DOI, they describe the same deposited record. If one entry has no DOI, or the DOIs differ, treat the pair as unresolved and continue with the checks below before merging.
2. Compare title, authors, and year as a set. Match the full title, the author list, and the publication year together. A shared title with a different author list or year points to two distinct records, such as a conference version and a journal version.
3. Check publication status. Look for a preprint label on either entry. The NIH Preprint Pilot labels eligible life-science preprints in PMC and PubMed as preprints so readers can distinguish publication status. If one entry is a preprint and the other is the published version, keep them as two clearly distinguished records and note the relationship in your notes instead of merging.
4. Check for a correction or erratum. If one entry is a correction notice tied to the other paper, it is a separate item with its own metadata. Keep it separate so the correction stays traceable to the article it amends.
5. Merge only the confirmed duplicates. When DOI, title, authors, and year all agree and neither entry is a preprint or correction, merge them. Zotero's duplicate detection provides a merge interface that preserves collections and tags while combining item records, so your filing and tags carry over to the merged item.
6. Verify the merged record. After merging, reopen the item and confirm the DOI, author list, and year survived, and that your notes and tags are attached to the single remaining entry. If a field is missing, restore it from the metadata you recorded in step 1.
When the checks leave the pair unresolved, keep both entries and add a short note in each explaining what you compared and what still differs. That keeps your citations traceable while you finish the paper.