This book sets out to give an account of the principles and more elementary techniques of statistical reasoning, particularly as they are relevant to the biologist. I have tried to keep the use of symbolism and mathematical jargon to a minimum and, except in a very few sections, there is nothing assumed beyond that normally contained in a school elementary mathematics course. I have attempted rather to concentrate on the exposition of ideas, because I believe that when a scientist first realizes his need for statistical tools it is their meaning rather than their procedure which causes him difficulty. Once the logic is clear it is relatively easy to follow the form of the calculations.

The chapters are arranged for consecutive reading; a few sections of a slightly mathematical nature, which can be omitted at a first reading, are marked with an asterisk after the section number. A decimal system is used for this numbering.

The first chapter aims to show the need for statistical procedures in experiments and surveys, and does not contain any techniques. Chapters 2, 3 and 4 deal with the simpler non-parametric methods, with particular emphasis on the logic of statistical reasoning; I believe that this is easier to follow in non-parametric procedures than in normal distribution methods. Chapter 5 is concerned with decision theory ideas, which seem certain to have an increasing effect on statistical practice.