Predatory journals…prioritize self-interest at the expense of scholarship and are characterized by false or misleading information, deviation from best editorial and publication practices, a lack of transparency, and/or the use of aggressive and indiscriminate solicitation practices.

--Grudniewicz A, Moher D, Cobey KD, et al. Predatory journals: no definition, no defence. Nature 2019; 576: 210-212. PMID: 31827288.

Predatory journals know you need to publish and take advantage of that need. They will get your article online, but it will be in a journal no one has head, that is not indexed in a major database like PubMed, CINAHL, Scopus, or Web of Science, and that doesn't provide copy-editing or even peer review. Your article is published but is lost to other authors. Even though the article processing charge might be low, others will not be able to find it.

There are signs to look for but remember:

• Not all low-quality journals are predatory or published with malicious intent.
• They may be published by well-intentioned but inexperienced people who don't understand the basics of journal publishing.
• This doesn't make them predatory, but you still probably don't want to publish in them.

• the journal promises peer review turnaround time of only a week or two (or less!).
• there is no mention of copy-editing.
• the journal website has very few articles per issue.
• the journal is overly broad in scope (i.e., the Iowa Journal of Medicine, Dentistry, Nursing, and Public Health).
• the publisher publishes many journals, started at the same time or who all have the same editor.
• the website says the journal is open access gives little or vague information on fees.
• there are typos and grammar issues on the website.
• there is no physical address or phone number for the publisher.

The most important of these is probably the first two -- the promise of rapid peer review and the lack of copy-editing. Peer review takes time and all good journals provide copy-editing to make your article better.

• A journal claims to be "indexed in PubMed" but the only articles in PubMed are ones arising from NIH research.
  • Check the PubMed journal listings to see if all of a publication's articles are included or only the ones required to be included in PubMed Central by NIH.
  • Having all articles from a journal included in PubMed requires the journal to meet the quality standards for PubMed Central or the more rigorous standards for MEDLINE, which accepts only about 13% of the journals which apply for inclusion annually.
  • If an article arising from NIH funding is published in a predatory journal, that article must still be included in PMC and in PubMed.
  • MEDLINE, PubMed, and PubMed Central: how are they different?
• The journal advertises an impact factor, but it's not included in Journal Citation Reports (JCR).
  • JCR is the official source of the Journal Impact Factor (JIF). Some journals calculate their own JIFs, but it's important to be able to compare a JIF with those of other journals within a category, such as Pediatrics or Dentistry. 
• The journal or its publisher is not listed by the Directory of Open Access Journals or the Open Access Scholarly Publishing Association. Both require transparency and best practices. 
• Did you get an email asking you to write an article or even edit an issue?  Evaluate it carefully-- although some legitimate journals send requests like this, it's more likely to be a template from an unscrupulous publisher.  Don't click links in the email; instead, google for the journal or publisher to find their website.

• NIH Statement on Article Publication Resulting from NIH Funded Research (Guide Notice OD-18-011)
• Authors Responsibilities re Predatory or Pseudo Journals (International Committee of Medical Journal Editors)
• Identifying Predatory or Pseudo Journals (World Association of Medical Editors)
• Think. Check. Submit. (From representatives of publishing-related groups including the Association of University Presses, the Committee on Publication Ethics, the International Association of STM Publishers, and others)