Agricultural Statistical Data Analysis Using Stata

253 Pages·2013·15.918 MB·English

by  George Boyhan

Statistics A
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Agricultural c
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Statistical Data u
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Analysis Using Stata
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Practical statistics is a powerful tool used frequently by agricultural researchers and t
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graduate students involved in investigating experimental design and analysis. One c
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of the most widely used statistical analysis software packages for this purpose is
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Stata. The Stata software program has matured into a user-friendly environment D
with a wide variety of statistical functions. Agricultural Statistical Data Analysis
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Using Stata introduces readers to the use of Stata to solve agricultural statistical t
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problems.

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The book begins with an overview of statistical software and the Stata program. It n
explains the various windows and menus and describes how they are integrated. The a
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next chapters explore data entry and importing as well as basic output formats and y
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descriptive statistics. The author describes the ever-increasing design complexity
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and how this is implemented in the software. He reviews one of Stata’s strongest

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features, which is its programming ability. He also examines post hoc tests as well
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as Stata’s graphing capabilities. The final chapters provide information on regression
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analysis, data transformations, and the analyses of nonparametric data.
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Many agricultural researchers are unprepared for the statistics they will need to S
use in their profession. Written in an easy-to-read format with screen shots and t
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illustrations, the book is suitable for a wide audience, including beginners in statistics t
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who are new to Stata, as well as more advanced Stata users and those interested
in more complex designs.
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K20263_Cover.indd 1 5/8/13 9:50 AM

Agricultural
Statistical Data
Analysis Using Stata
George E. Boyhan
CRC Press
Taylor & Francis Group
6000 Broken Sound Parkway NW, Suite 300
Boca Raton, FL 33487-2742
© 2013 by Taylor & Francis Group, LLC
CRC Press is an imprint of Taylor & Francis Group, an Informa business
No claim to original U.S. Government works
Version Date: 20130503
International Standard Book Number-13: 978-1-4665-8586-7 (eBook - PDF)
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To Dr. Norton who answered the phone
over the Christmas holidays

Contents
IntroductIon vii
About the Author xi
chApter 1 GenerAl StAtIStIcAl pAckAGeS compArISonS 1
Program 3
Windows and Menus 4
What’s on the Menu? 13
Conclusion 27
chApter 2 dAtA entry 29
Importing Data 32
Manipulating Data and Formats 44
chApter 3 deScrIptIve StAtIStIcS 55
Output Formats 60
Experimentation Ideas 60
chApter 4 two SAmple teStS 63
ANOVA 69
Output and Meaning 71
chApter 5 vArIAtIonS of one fActor AnovA deSIGnS 75
Randomized Complete Block Design 75
Latin Square Designs 80
Balanced Incomplete Block Designs 84
Balanced Lattice Designs 88
Group Balanced Block Design 92
Subsampling 96
v
vi Contents
chApter 6 two And more fActorS AnovA 101
Split-Plot Design 106
Split-Block Design 109
Evaluation over Years or Seasons 114
Three-Factor Design 118
Split-Split Plot Design 120
Covariance Analysis 125
chApter 7 proGrAmmInG StAtA 133
chApter 8 poSt hoc teStS 147
Planned Comparisons 147
Built-in Multiple Range Tests 151
Programming Scheffé’s Test 157
chApter 9 prepArInG GrAphS 167
Graphing in Stata 167
chApter 10 correlAtIon And reGreSSIon 179
Correlation 179
Linear Regression 183
chApter 11 dAtA trAnSformAtIonS 203
chApter 12 bInAry, ordInAl, And cAteGorIcAl
dAtA AnAlySIS 215
AppendIx 231
referenceS 237
Introduction
Stata is a statistical software package that began as a command-line
program. A graphical user interface (GUI) was added to the program
sometime after its introduction, which has generally been very well
executed. It allows beginners and novice users to conduct statistical
procedures without having to type commands that can become rather
complex with certain models. The command-line approach is never
very far away and, as you gain confidence with the program, you will
find yourself using it more and more.
The program has matured into a user-friendly environment with
a wide variety of statistical functions. A couple of nice features
that have dramatically improved usability are being able to have a
dataset visible on the desktop, while analyzing data and help menus
that indicate where in the menus the specific statistical function
can be found.
This book will attempt to introduce the reader to using Stata to
solve agricultural statistical problems. Stata, as a general purpose sta-
tistical program, has a large suite of commands that are applicable in
a variety of disciplines. Based on the number and scope of textbooks
available on Stata, it has a strong following in medical, large popula-
tion, and regression analyses. This is not to detract from its overall
capabilities to solve a wide range of problems.
vii
viii IntroduCtIon
This book provides an overview of using the Stata program. It
includes a discussion of the various menus, many of the dialog boxes,
and an explanation of how the parts are integrated.
An explanation of how data can be entered into the program or
imported is also presented. Surprisingly, for those new to statistical
software and analyses, this can be one of the most time-consuming
aspects of statistics. Stata has a very in-depth set of capabilities for
entering, importing, and manipulating data prior to analyses.
This is followed by a chapter on the simplest of descriptive statis-
tics. An ever-increasing level of complexity as different models and
approaches to agricultural statistical problems are introduced follows.
One of the biggest changes in Stata is the ability to create graphs. This
gives the Stata user another tool in preparing results for presentation
and publication.
This book attempts to explain how to use Stata to analyze agricul-
tural experiments. Data that violate the underlying assumptions in
many parametric tests must be handled differently. This may involve
transformation or the use of nonparametric tests. Various examples
from agricultural experiments are covered.
Agricultural Statistical Data Analysis Using Stata includes the more
important statistical procedures used in agricultural research. Various
experimental designs and how to handle them within Stata are dis-
cussed. Analysis of variance and covariance applications for agri-
cultural experiments is covered. Post hoc tests and comparisons are
covered as well. How to perform regression and correlations with
some agricultural examples is included.
The more important nonparametric tests used in agricultural
research are also covered—in particular, the use of chi-square for cat-
egorical data, such as from inheritance studies.
As mentioned earlier, Stata grew out of a command-line inter-
face, which is still recognizable as part of its foundation. In fact,
this command-line interface is one of its strongest attributes because
these commands can be organized and executed as a program, which
expands the capabilities of Stata and ultimately makes things easier
for users willing to devote some time to developing unique programs
to solve their particular problems. An introduction to programming
Stata is included, which should help users in this area. How to pro-
gram Stata to extend its usability is also covered. Multiple-range tests