These pages are based on materials from http://mindtools.net, a site which I have maintained for many years and has had many hundreds of thousands of visitors from around the world. These pages represent my individual research and opinions and are written by me unless otherwise noted. Many of the materials are suitable for use by high school and college students. Some of these pages will provide links back to materials, such as quizzes and slideshows, on the original mindtools.net site.  — Anthony Birch, Ph.D.