Page 14 - Statistics for Environmental Engineers

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The Aim of this Book
Learning statistics is not difficult, but engineers often dislike their introductory statistics course. One
reason may be that the introductory course is largely a sterile examination of textbook data, usually
from a situation of which they have no intimate knowledge or deep interest. We hope this book, by
presenting statistics in a familiar context, will make the subject more interesting and palatable.
The book is organized into short chapters, each dealing with one essential idea that is usually developed
in the context of a case study. We hope that using statistics in relevant and realistic examples will make
it easier to understand peculiarities of the data and the potential problems associated with its analysis.
The goal was for each chapter to stand alone so the book does not need to be studied from front to back,
or in any other particular order. This is not always possible, but the reader is encouraged to “dip in”
where the subject of the case study or the statistical method stimulates interest.
Most chapters have the following format:

• Introduction to the general kind of engineering problem and the statistical method to be
discussed.
• Case Study introduces a specific environmental example, including actual data.
• Method gives a brief explanation of the statistical method that is used to prepare the solution
to the case study problem. Statistical theory has been kept to a minimum. Sometimes it is
condensed to an extent that reference to another book is mandatory for a full understanding.
Even when the statistical theory is abbreviated, the objective is to explain the broad concept
sufficiently for the reader to recognize situations when the method is likely to be useful, although
all details required for their correct application are not understood.
• Analysis shows how the data suggest and influence the method of analysis and gives the
solution. Many solutions are developed in detail, but we do not always show all calculations.
Most problems were solved using commercially available computer programs (e.g.,
MINITAB, SYSTAT, Statview, and EXCEL).
• Comments provide guidance to other chapters and statistical methods that could be useful
in analyzing a problem of the kind presented in the chapter. We also attempt to expose the
sensitivity of the statistical method to assumptions and to recommend alternate techniques
that might be used when the assumptions are violated.
• References to selected articles and books are given at the end of each chapter. Some cover
the statistical methodology in greater detail while others provide additional case studies.
• Exercises provides additional data sets, models, or conceptual questions for self-study or
classroom use.

Summary

To gain from what statistics offer, we must proceed with an attitude of letting the data reveal the critical
properties and of selecting statistical methods that are appropriate to deal with these properties. Envi-
ronmental data often have troublesome characteristics. If this were not so, this book would be unneces-
sary. All useful methods would be published in introductory statistics books. This book has the objective
of bringing together, primarily by means of examples and exercises, useful methods with real data and
real problems. Not all useful statistical methods are included and not all widely encountered problems
are discussed. Some problems are omitted because they are given excellent coverage in other books
(e.g., Gilbert, 1987). Still, we hope the range of material covered will contribute to improving the state-
of-the-practice of statistics in environmental engineering and will provide guidance to relevant publica-
tions in statistics and engineering.

© 2002 By CRC Press LLC