Since the different kinds of statistics to be described in this book will be carried out with one of the, if not the, most widely used and comprehensive statistical programs in the social sciences, SPSS, we will begin by outlining what this entails. The abbreviation SPSS stands for Statistical Package for the Social Sciences. This package of programs is available for personal computers. These programs are being continuously updated, and so there are various versions in existence. This book covers the latest version of SPSS, Version 19, which we shall refer to as SPSS for short unless otherwise indicated. Previous editions of this book have described earlier versions of SPSS (Bryman & Cramer, 1990, 1994, 1997, 1999, 2001, 2005, 2009). As Version 19 is very similar to Releases 18, 17, 16 and 15, this book can also be used for these earlier versions.