This book has been written at an elementary mathematical level and requires no more than high school mathematics to understand. Nevertheless, you may find Chapters4and5alittledifficultatfirst.Thesechaptersonprobabilityanddistributions are basic building blocks for subsequent concepts, however, and you should study them carefully. The basic concepts of estimation and hypothesis testing are covered by the end of Chapter 8, and this is followed in Chapter 9 by some more advancedconcepts–butalwaysexplainedinsimplelanguage–thatunderliemany types of analysis now commonly used by geneticists and epidemiologists. The next threechapterscoverspecialstatisticalmethodsthatarewidelyusedinbothgenetic and epidemiological research. There is no attempt, on the other hand, to go into any detail on the advanced statistical methods of analysis used in the special field ofgeneticepidemiology–thiswouldbeabookinitself.Inthelastchapterwehave tried to review the most important concepts introduced in earlier chapters as they relate to a critical reading of reports published in the literature.