Long before I had any inkling that I would write a book, I learned that apreface is the author''s attempt to engage the reader in a leisurely conversation before serious joint work begins. In that spirit, I ask you to spend a moment with me now. Although an important focus of my training and daily work is in mathematics and statistics, I have found that many health care workers in general, and physicians in particular, have difficulty understanding research issues when they are presented mathe matically. Statistical principles in medicine are relatively straight forward and can be'' easily absorbed without a heavy mathematical preamble. I have come to believe that the underlying research principles are not difficult; what is difficult is the mathematics in which the principles are embedded. The mathematical medium often distorts and confuses the research message for nonmathe maticians. I wrote this book to explain the statistical principles in health care in fairly nonmathematical terms.
