Step 1: Check the peer review status of the JOURNAL.
Step 2: If the JOURNAL is peer reviewed, then assess the ARTICLE.
A technical defintion...
"That which is produced on all levels of govenment, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers."
(Fourth International conference on Grey Literature, Washington D.C., October 1999)
Examples of grey literature may include:
Market research reports
Newsletters and/or bulletins
Dissertations & Theses
Examples of why you might use grey literature: