I'm aware that it's a violation of terms for most publishers to submit the same article to more than one journal, but I frequently see authors whose papers seem very similar, particularly papers released in a single year. In my field, neuroscience, this is particularly true about conference papers; one researcher will often have numerous posters/conference papers about seemingly the same topic. What are the guidelines for acceptability regarding this type of behavior?
According to the Committee on Publication Ethics Guidelines on Good Publication Practice, the term "redundant publication" is defined this way:
"Redundant publication occurs when two or more papers, without full cross reference, share the same hypothesis, data, discussion points, or conclusions." In addition, it states: "(1) Published studies do not need to be repeated unless further confirmation is required. (2) Previous publication of an abstract during the proceedings of meetings does not preclude subsequent submission for publication, but full disclosure should be made at the time of submission. (3) Re-publication of a paper in another language is acceptable, provided that there is full and prominent disclosure of its original source at the time of submission. (4) At the time of submission, authors should disclose details of related papers, even if in a different language, and similar papers in press." Note that (2) states that it is generally acceptable to present a paper in a conference and then later publish exactly the same paper in a journal, as long as you mention to the editor that the paper has been publicly presented.
According to the paper Science journal editors’ views on publication ethics: Results of an international survey,
"Breaches of publication ethics such as plagiarism, data fabrication and redundant publication are recognised as forms of research misconduct that can undermine the scientific literature." It also stated that redundant publication is an unethical practice. Of 16 ethical issues studied, redundant publication had the highest severity (that is, it caused editors the most concern---more than plagiarism or data fabrication).