An Erratum is a statement by the authors of the original article that briefly describes any corrections resulting from errors or omissions, such as an incorrect value in a table, a mislabeled figure, or a missing reference. Any effects on the conclusions of the article must be noted. The corrected article is not removed from the online journal; instead, a notice of the erratum is published. The erratum is freely available to all readers and is linked to the corrected article.

A Publisher’s Note notifies readers that an article has been corrected after publication. It is issued by the publisher when typographical or production errors that are the publisher’s responsibility affect the integrity of the article’s metadata (such as the title, author list, or byline) or significantly affect readers’ ability to understand the article. Publisher’s Notes are freely available to all readers.

In such cases, the original article is removed and replaced with a corrected version, and the date of the correction is noted on the corrected article. An original article can only be replaced within one year of its original publication date; corrections to articles published more than one year earlier are documented by a Publisher’s Note only.

Minor errors that do not affect the integrity of the metadata or readers’ understanding, and that do not involve a scientific error or omission, are corrected at the discretion of the publisher.

An Expression of Concern may be issued by the editors when there are serious concerns about the reliability of an article or the conduct of the research, but the evidence is not yet conclusive, for example while an investigation by the authors’ institution is still in progress. The notice alerts readers to the concern and is linked to the article. Depending on the outcome of the investigation, it may later be followed by a correction or a retraction, or it may be withdrawn.

A Retraction is a notice that an article should no longer be regarded as part of the scientific literature. Retractions are issued when there is clear evidence that:

• the findings are unreliable, as a result of misconduct (such as data fabrication or falsification) or honest error (such as a miscalculation or experimental error);
• the findings have previously been published elsewhere without proper referencing, permission, or justification (redundant publication);
• the work is plagiarized; or
• the work reports unethical research, for example research involving students without appropriate consent.

To protect the integrity of the record, a retracted article is not removed from the online journal. A retraction notice is published, made freely available to all readers, and linked to the retracted article, which is clearly marked as “Retracted”.

Authors may request a retraction when they discover substantial errors in their work; in other cases, the editors or the publisher may conclude that retraction is appropriate. Every retraction notice states the reason for the retraction and who is responsible for the decision. If a retraction is made without the unanimous agreement of the authors, this is also noted.

In rare and extreme cases involving legal infringement, such as defamation, copyright infringement, or a serious risk to the privacy of research participants, the publisher may redact or remove an article. Its bibliographic information is retained to preserve the integrity of the scientific record.