Statistics for Veterinary and Animal Science

414 Pages·2013·11.17 MB·English

by  Aviva Petrie

Statistics for Veterinary and
Animal Science

Statistics for Veterinary and
Animal Science
Third Edition
Aviva Petrie
, BSc, MSc, CStat, CSci, FHEA
Senior Lecturer in Statistics and Head of the Biostatistics Unit
UCL Eastman Dental Institute
University College London
Honorary Lecturer in Medical Statistics
London School of Hygiene and Tropical Medicine
University of London
London
UK
Paul Watson
, BSc, BVetMed, PhD, DSc, FRCVS
Emeritus Professor of Reproductive Cryobiology
The Royal Veterinary College
University of London
London
UK
A John Wiley & Sons, Ltd., Publication
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Cover image: Horse illustration: all-silhouettes.com
Pig and dog illustration: Neubau Welt
Cover design by www.hisandhersdesign.co.uk
Set in 10/12 pt Times Ten by Toppan Best-set Premedia Limited
1 2013
Contents
Preface to third edition ix
Preface to second edition xi
Preface to first edition xiii
About the companion website xv
 1 The whys and wherefores of statistics  1
1.1 Learning objectives 1
1.2 Aims of the book 1
1.3 What is statistics? 2
1.4 Statistics in veterinary and
animal science 3 4.3 Statistical inference 46
1.5 Evidence-based veterinary medicine 4 4.4 Sampling distribution of
1.6 Types of variable 4 the mean 48
1.7 Variations in measurements 5 4.5 Confidence interval for a mean 50
1.8 Terms relating to measurement 4.6 Sampling distribution of the
quality 7 proportion 52
1.9 Populations and samples 9 4.7 Confidence interval for a
1.10 Types of statistical procedures 10 proportion 53
1.11 Conclusion 10 4.8 Bootstrapping and jackknifing 53
Exercises 10 Exercises 54
 2 Descriptive statistics  12  5 Experimental design and 
2.1 Learning objectives 12 clinical trials  55
2.2 Summarizing data 12 5.1 Learning objectives 55
2.3 Empirical frequency distributions 12 5.2 Types of study 55
2.4 Tables 14 5.3 Introducing clinical trials 59
2.5 Diagrams 15 5.4 Importance of design in the
2.6 Numerical measures 19 clinical trial 60
2.7 Reference interval 24 5.5 Control group 61
Exercises 25 5.6 Assignment of animals to the
treatment groups 62
 3 Probability and probability  5.7 Avoidance of bias in the
distributions  28 assessment procedure 65
3.1 Learning objectives 28 5.8 Increasing the precision of the
3.2 Probability 28 estimates 66
3.3 Probability distributions 30 5.9 Further considerations 68
3.4 Discrete probability the population E4x6ercises 73
vi Contents
 6 An introduction to hypothesis testing  75 9.5 Testing associations in an r × c
6.1 Learning objectives 75 contingency table 117
6.2 Introduction 75 9.6 Comparing two proportions:
6.3 Basic concepts of hypothesis paired observations 120
testing 75 9.7 Chi-squared goodness-of-fit test 122
6.4 Type I and Type II errors 79 Exercises 123
6.5 Distinction between statistical
and biological significance 80 10 Linear correlation and regression  126
6.6 Confidence interval approach to 10.1 Learning objectives 126
hypothesis testing 81 10.2 Introducing linear correlation
6.7 Collecting our thoughts on and regression 126
confidence intervals 82 10.3 Linear correlation 127
6.8 Equivalence and non-inferiority 10.4 Simple (univariable) linear
studies 82 regression 132
Exercises 83 10.5 Regression to the mean 142
Exercises 142
 7 Hypothesis tests 1 – the t-test: 
comparing one or two means  85 11 Further regression analyses  146
7.1 Learning objectives 85 11.1 Learning objectives 146
7.2 Requirements for hypothesis 11.2 Introduction 146
tests for comparing means 85 11.3 Multiple (multivariable) linear
7.3 One-sample t-test 87 regression 147
7.4 Two-sample t-test 89 11.4 Multiple logistic regression:
7.5 Paired t-test 92 a binary response variable 154
Exercises 96 11.5 Poisson regression 159
11.6 Regression methods for
 8 Hypothesis tests 2 – the F-test:  clustered data 161
comparing two variances or more   Exercises 163
than two means  100
8.1 Learning objectives 100 12 Non-parametric statistical methods  165
8.2 Introduction 100 12.1 Learning objectives 165
8.3 The F-test for the equality of 12.2 Parametric and non-parametric
two variances 100 tests 165
8.4 Levene’s test for the equality 12.3 Sign test 167
of two or more variances 102 12.4 Wilcoxon signed rank test 169
8.5 Analysis of variance (ANOVA) 12.5 Wilcoxon rank sum test 171
for the equality of means 102 12.6 Non-parametric analyses of
8.6 One-way analysis of variance 105 variance 173
Exercises 109 12.7 Spearman’s rank correlation
coefficient 175
 9 Hypothesis tests 3 – the Chi-squared  Exercises 178
test: comparing proportions  112
9.1 Learning objectives 112 13 Further aspects of design 
9.2 Introduction 112 and analysis  181
9.3 Testing a hypothesis about a 13.1 Learning objectives 181
single proportion 112 13.2 Transformations 181
9.4 Comparing two proportions: 13.3 Sample size 184
independent groups 113 13.4 Sequential and interim analysis 189
Contents vii
13.5 Meta-analysis 190 17.3 REFLECT statement (livestock
13.6 Methods of sampling 194 and food safety RCTs) 254
Exercises 198 17.4 ARRIVE guidelines (research
using laboratory animals) 255
14 Additional techniques  200
17.5 STROBE statement
14.1 Learning objectives 200
(observational studies) 255
14.2 Diagnostic tests 200
17.6 STARD statement (diagnostic
14.3 Bayesian analysis 208
accuracy) 256
14.4 Measuring agreement 211
17.7 PRISMA statement (systematic
14.5 Measurements at successive
reviews and meta-analysis) 256
points in time 218
14.6 Survival analysis 221
18 Critical appraisal of reported 
14.7 Multivariate analysis 226
studies  269
Exercises 227
18.1 Learning objectives 269
18.2 Introduction 269
15 Some specialized issues and 
18.3 A template for critical appraisal
procedures  230
of published research involving
15.1 Learning objectives 230
animals 270
15.2 Introduction 230
18.4 Paper 1 273
15.3 Ethical and legal issues 230
18.5 Critical appraisal of paper 1 284
15.4 Spatial statistics and geospatial
18.6 Paper 2 288
information systems 233
18.7 Critical appraisal of paper 2 297
15.5 Veterinary surveillance 237
18.8 General conclusion 302
15.6 Molecular and quantitative
genetics 240
  Solutions to exercises  303
Exercises 242
16 Evidence-based veterinary medicine  243   Appendices  323
16.1 Learning objectives 243 A Statistical tables 323
16.2 Introduction 243 B Tables of confidence intervals 339
16.3 What is evidence-based C Glossary of notation 341
veterinary medicine? 244 D Glossary of terms 345
16.4 Why has evidence-based E Flowcharts for selection of
veterinary medicine developed? 244 appropriate tests 368
16.5 What is involved in practising
evidence-based veterinary   References  371
medicine? 245
16.6 Integrating evidence-based Index 379
veterinary medicine into
clinical practice 249 Colour plate section can be found facing
16.7 Example 249 page 240
Exercises 250
17 Reporting guidelines  252
17.1 Learning objectives 252
17.2 Introduction to reporting
guidelines (EQUATOR network) 252