One way to decide if a journal is peer reviewed is to look it up on Ulrichsweb. The description will tell you if it is "refereed" and that is another way of saying that articles in that journal undergo "peer review." 

From Poultry Science: http://ps.oxfordjournals.org/content/92/1/225

From Science: http://www.jstor.org/stable/3074252?seq=1#page_scan_tab_contents

• Does the source have a bibliography? This can lead you to other sources.
• Is there an author listed as part of the citation? Judging authority can be difficult without an author.
• Is the journal refereed (peer reviewed)?
• How old is the source? Will this matter for your topic? Currency of information can be important. Some aspects of a topic may need currency more than others.
• What other terminology is being used either by the author or by the database? Keep an eye out for other words you can use in your search statements.
• Does The Valley Library own the journal (either in print or electronically)? If we don't own it, it will take more time to get your hands on the source.