The Users' Guides to the Medical Literature was originally published as a 25 part series in JAMA between 1993-2000. Some of the most relevant articles from the series are listed below. The current Users' Guides (2nd edition, 2008) are published as a book (see link to online version below or read the print copy located on the second floor of the Health Sciences Library at MU HSL Reference WB 39.U845 2008).
Dawson. Basic and Clinical Biostatistics. 4th ed. McGraw-Hill, 2004. (Especially Chapter 13: "Reading the Medical Literature").