The apparent authenticity of published data can be as dangerous as it is inviting. This guide points out the main dangers (sampling errors, measurement errors, and invalid or unreliable procedures) and analyzes the various ways in which these problems arise -- giving numerous examples. Jacob discusses ways to solve these problems, and when no solutions seem available, he suggests appropriate disclaimers. An appendix critically evaluates several useful data sets. This monograph also serves as a general reference volume on how to avoid the pitfalls that researchers often overlook. `Its subject is one that should find a place in many more introductory social statistics and research methods texts that it actually does.' -- The Statistician, Vol 35, 1986