An investigation conducted on behalf of the journal by Elsevier's Research Integrity & Publishing Ethics team has determined that the authors were requested by two of the reviewers to insert 26 references to their paper during the peer-review process. As these citations were requested by individuals who could influence the decision to accept the article, the authors are not considered at fault for the addition of these citations. The Editors have determined that the citations added to the paper at the request of the reviewers do not offer a balanced reflection of the literature.
A Sun, study studied this question.