Veterinary Clinical Epidemiology: From Patient to Population

Cover
Half Title
Title Page
Copyright Page
Contents
List of Examples
Preface to the Fourth Edition
Acknowledgments
About the Cover
Author
Chapter 1: Introduction
1.1 Definitions
1.2 Epidemiologic Approaches
1.2.1 Quantitative Epidemiology
1.2.2 Ecological Epidemiology (Medical Ecology)
1.2.3 Etiologic Epidemiology
1.2.4 Herd Health/Preventive Medicine
1.2.5 Clinical Epidemiology
1.3 Applications of Epidemiology in Veterinary Practice
1.4 Objectives
1.4.1 Development of Medical Decision-Making Skills
1.4.2 Learn Epidemiologic Methodology and How to Analyze and Present Data
1.4.3 Learn to Read the Medical Literature Critically
References
Answers to Follow-Up Questions
Chapter 2: Defining the Limits of Normality
2.1 Introduction
2.2 Properties of Clinical Measurements
2.2.1 Signs and Symptoms: Objective versus Subjective Data
2.2.2 Scales
2.2.3 Clinical Staging
2.2.4 Validity and Reliability
2.2.5 Variation
2.2.5.1 Measurement Variation
2.2.5.2 Biological Variation
2.2.5.3 How to Reduce the Effects of Variation
2.3 Distributions
2.3.1 Basic Properties of Distributions
2.3.2 Shapes of Naturally Occurring Distributions
2.3.2.1 Unimodal, Bimodal, and Multimodal
2.3.2.2 Symmetry, Skewness, and Kurtosis
2.3.2.3 Factors Influencing the Shape of Frequency Distributions
2.3.3 The Normal Distribution
2.4 Reference Ranges and the Criteria for Abnormality
2.4.1 Abnormal as Unusual
2.4.2 Abnormal as Associated with Disease
2.4.3 Abnormal as Detectable or Treatable
References
Answers to Follow-Up Questions
Chapter 3: Evaluation of Diagnostic Tests
3.1 Introduction
3.2 Test Accuracy
3.2.1 The Standard of Validity (Gold Standard)
3.2.2 Postmortem Examination as a Diagnostic Test
3.3 Properties of Diagnostic Tests
3.3.1 Sensitivity and Specificity (True Positive and True Negative Rates)
3.3.2 False Positive and Negative Rates
3.3.3 Predictive Values
3.3.4 The Effect of Prevalence on Predictive Values
3.3.5 Likelihood Ratios
3.3.6 Accuracy, Reproducibility, and Concordance
3.4 Interpretation of Tests Whose Results Fall on a Continuum
3.4.1 Trade-Offs between Sensitivity and Specificity
3.4.2 Receiver Operating Characteristic Curve
3.4.3 Two-Graph Receiver Operating Characteristic Analysis
3.4.4 Selecting a Cutoff
3.5 Comparison of Diagnostic Tests
3.5.1 Tests with Fixed Cutoffs
3.5.2 For Test Results That Fall on a Continuum
3.6 Sources of Bias in the Evaluation of Diagnostic Tests
3.6.1 Relative versus True Sensitivity and Specificity
3.6.2 The Spectrum of Patients
3.6.3 Bias in Associating Test Results with Disease
3.7 Statistical Significance
References
Answers to Follow-Up Questions
Chapter 4: Use of Diagnostic Tests
4.1 Introduction
4.2 Calculation of the Probability of Disease
4.2.1 From a Two-by-Two Table
4.2.2 Use of Bayes’ Theorem
4.2.3 Use of the Likelihood Ratio to Calculate Post-Test Probabilities
4.2.3.1 Conversion between the Probability of Disease and the Odds of Disease
4.2.3.2 Calculation of the Post-Test Probability of Disease
4.2.3.3 A Nomogram for Applying Likelihood Ratios and Bayes’ Theorem
4.2.3.4 Estimating Post-Test Probability of Disease from the Magnitude of a Test Result
4.2.4 Use of Post-Test Probabilities in Medical Decision-Making
4.3 Multiple Tests
4.3.1 Parallel Testing
4.3.2 Serial Testing
4.3.3 Herd Retest
4.3.4 Assumption of Independence of Multiple Test Results
4.4 Working with Differential Lists
4.4.1 Rule-Ins and Rule-Outs: The Choice of Sensitive or Specific Tests
4.5 Screening for Disease
4.5.1 Definitions
4.5.2 Test Criteria
4.6 Increasing the Predictive Value of Diagnostic Tests
4.7 Communication of Diagnostic Test Results
References
Answers to Follow-Up Questions
Chapter 5: Measuring the Commonness of Disease
5.1 Introduction
5.2 Expressing the Frequency of Clinical Events
5.2.1 Proportions, Rates, and Ratios
5.2.2 Prevalence, Incidence, and Attack Rate
5.3 Measuring the Frequency of Clinical Events
5.3.1 Prevalence
5.3.2 Incidence
5.4 Factors Affecting the Interpretation of Incidence and Prevalence
5.4.1 Temporal Sequence
5.4.2 Disease Duration
5.4.3 Relationship among Incidence, Prevalence, and Duration of Disease
5.4.4 True versus Apparent Prevalence
5.4.5 Case Definition
5.4.6 Dangling Numerators
5.4.7 Population at Risk
5.4.8 Crude versus Adjusted Rates
5.5 Adjusted Rates: The Direct Method
5.5.1 Age-Adjusted Rates
5.5.2 Rate Adjustment for Other Factors
5.5.3 The Choice of a Standard Population
5.5.4 When to Adjust Rates
5.5.5 The Uses of Incidence and Prevalence
References
Answers to Follow-Up Questions
Chapter 6: Risk Assessment and Prevention
6.1 Risk Factors and Their Identification
6.2 Factors That Interfere with the Assessment of Risk
6.3 Uses of Risk
6.4 Comparison of Risks
6.4.1 Univariate Analysis
6.4.2 Multivariate Analysis
6.4.2.1 Mantel-Haenszel Stratified Analysis
6.4.2.2 Multivariate Logistic Regression Analysis
6.5 Cohort Studies of Risk
6.5.1 True Cohort Study Designs
6.5.1.1 Concurrent Cohort Studies
6.5.1.2 Historical Cohort Studies
6.5.2 Comparing Risks in Cohort Studies
6.5.2.1 Relative Risk
6.5.2.2 Attributable Risk
6.5.2.3 Population Attributable Risk
6.5.2.4 Population Attributable Fraction
6.5.3 Limitations of Cohort Studies
6.5.4 Case Series
6.6 Case-Control Studies of Risk
6.6.1 Advantages of Case-Control Studies
6.6.2 Comparing Risks in Case-Control Studies
6.6.3 The Odds Ratio
6.6.4 Bias in Case-Control Studies
6.6.4.1 Bias in Selecting Groups
6.6.4.2 Bias in Measuring Exposure
6.6.4.3 Presumed Temporal Relationships
6.7 Prevalence Surveys of Risk
6.7.1 Comparing Risks in Prevalence Surveys
6.7.2 Limitations of Prevalence Surveys
6.8 Biological Plausibility and Cross-Sectional Study Designs
References
Answers to Follow-Up Questions
Chapter 7: Measuring and Communicating Prognoses
7.1 Expressing Prognoses
7.2 Natural History versus Clinical Course
7.3 Prognosis as a Rate
7.4 Survival Analysis
7.4.1 Population Models
7.4.2 Cross-Sectional Studies
7.4.2.1 Analysis of Longevity
7.4.2.2 Life Table Analysis
7.4.3 Longitudinal Studies
7.4.4 Interpreting Survival Curves
7.5 Communication of Prognoses
References
Answers to Follow-Up Questions
Chapter 8: Design and Evaluation of Clinical Trials
8.1 Introduction
8.2 Efficacy, Effectiveness, and Compliance
8.3 Clinical Trials: Structure and Evaluation
8.3.1 Case Definition
8.3.2 Uncontrolled Clinical Trials
8.3.3 Comparisons across Time and Place
8.3.4 Allocating Treatment
8.3.5 Remaining in Assigned Treatment Groups
8.3.6 Assessment of Outcome
8.3.7 Placebo Effect
8.3.8 Statistical Analysis
8.4 Subgroups
8.5 Clinical Trials in Practice
References
Answers to Follow-Up Questions
Chapter 9: Statistical Significance
9.1 Introduction
9.2 Hypothesis Definition and Testing: An Overview
9.2.1 The Steps in Hypothesis Testing: An Example
9.2.2 Results and Conclusions
9.3 Interpretation of Statistical Analyses
9.3.1 Concluding a Difference Exists
9.3.1.1 The Null Hypothesis
9.3.1.2 Statistical Significance
9.3.1.3 Confidence Limits
9.3.1.4 Confidence Interval for a Rate or Proportion
9.3.1.5 One-Tailed versus Two-Tailed Tests of Significance
9.3.2 Concluding a Difference Does Not Exist
9.3.2.1 Statistical Significance
9.3.2.2 Power
9.3.3 Concluding an Association Exists
9.3.3.1 Agreement between Tests
9.3.3.2 Association between Two Variables
9.4 The Selection of an Appropriate Statistical Test
9.4.1 Censoring
9.4.2 Level of Measurement
9.4.3 Number of Groups
9.4.4 Nature of Groups
9.4.5 Number of Categories
9.4.6 Category Size
9.4.7 Data
9.5 Parametric and Nonparametric Tests
9.6 Sample Size
9.6.1 Minimum Sample Size for Demonstrating an Extreme Outcome
9.6.2 Minimum Sample Size for Estimating a Rate or Proportion with a Specified Degree of Precision
9.6.3 Minimum Sample Size to Detect Differences among Groups in Studies of Risk, Prognosis, and Treatment
9.7 Sampling Strategies
9.7.1 Probability Sampling
9.7.1.1 Simple Random Sampling
9.7.1.2 Systematic Sampling
9.7.1.3 Stratified Random Sampling
9.7.1.4 Cluster Sampling
9.7.2 Nonprobability Sampling
9.7.2.1 Consecutive Sampling
9.7.2.2 Convenience Sampling
9.7.2.3 Judgmental Sampling
9.8 Multiple Comparisons
References
Answers to Follow-Up Questions
Chapter 10: Medical Ecology and Outbreak Investigation
10.1 Introduction
10.2 Issues in the Epidemiology of a Disease
10.2.1 Occurrence
10.2.2 Cause
10.2.3 Susceptibility
10.2.4 Source
10.2.5 Transmission
10.2.6 Cost
10.2.7 Control
10.3 Outbreak Investigation
10.3.1 Descriptive Phase (Subjective, Objective Data)
10.3.2 Analytic Phase (Assessment)
10.3.3 Intervention (Plan)
Reference
Chapter 11: Measuring and Expressing Occurrence
11.1 Introduction
11.2 Case Definition
11.2.1 Based on Disease Signs, Symptoms, and Epidemiology
11.2.2 Based on Performance
11.3 Reporting Disease Occurrence
11.3.1 Host Distribution
11.3.1.1 Attack Rate
11.3.1.2 Crude versus Adjusted Rates
11.3.2 Temporal Distribution
11.3.2.1 Sporadic Disease
11.3.2.2 Endemic Disease
11.3.2.3 Epidemic Disease (Outbreak)
11.3.3 Time Series Analysis
11.3.4 Spatial Distribution
References
Answers to Follow-Up Questions
Chapter 12: Establishing Cause
12.1 Introduction
12.2 Multiple Causation of Disease
12.2.1 Agent Factors
12.2.2 Host Factors: Susceptibility
12.2.3 Environmental (Management) Factors
12.3 Sources of Bias in Evaluating Cause-Effect Relationships
12.3.1 Confounding
12.3.2 Interaction or Effect Modification
12.3.3 Multicollinearity
12.3.4 Procedure for Evaluating Interaction and Confounding
12.3.5 The Choice of Multivariate versus Stratified Analysis
12.4 Establishing Cause
12.4.1 Strength of Study Design
12.4.2 Temporal Relationship between Cause and Effect
12.4.3 Strength of the Association
12.4.4 Dose-Response Relationship
12.4.5 Biological Plausibility
12.4.6 Consistency
12.4.7 Elimination of Other Possibilities (Rule Out)
12.4.8 Reversible Associations
References
Answers to Follow-Up Questions
Chapter 13: Source and Transmission of Disease Agents
13.1 Sources of Infection
13.1.1 Iatrogenic Illnesses
13.1.2 Animal Reservoirs
13.1.3 Environment
13.2 Transmission
13.2.1 Mode of Transmission versus Route of Infection
13.2.2 Transmissible versus Non-Transmissible Diseases
13.3 Modes of Transmission
13.3.1 Horizontal Transmission
13.3.1.1 Direct Transmission
13.3.1.2 Indirect Transmission
13.3.1.3 Airborne Transmission
13.3.2 Vertical Transmission
13.4 Factors Affecting Communicability
13.4.1 Agent Factors
13.4.1.1 Life Cycle
13.4.1.2 Minimal Infective Dose
13.4.2 Host Factors
13.4.2.1 Heterogeneity
13.4.2.2 Immunity
13.4.3 Environmental Factors
13.4.3.1 Particle Diameter
13.4.3.2 Microclimate
References
Answers to Follow-Up Questions
Chapter 14: The Cost of Disease
14.1 Defining Disease in Economic Terms
14.1.1 The “Measures of Effect” Approach to Estimating Disease Impact
14.1.2 Partial Budgeting and Benefit-Cost Analysis
14.1.2.1 Partial Budgeting
14.1.2.2 Benefit-Cost Analysis
14.1.2.3 Discounting, Present and Future Value of Money
14.1.2.4 Decision Criteria in Benefit-Cost Analysis
14.2 Decision Analysis
14.2.1 Steps in Building a Decision Tree
14.2.1.1 Nodes
14.2.1.2 Utilities
14.2.1.3 Variables
14.2.2 Analysis of the Decision Tree
14.2.2.1 Fold Back
14.2.2.2 Sensitivity Analysis
14.2.2.3 Risk Profile Analysis
14.3 Scenario (Event) Trees
14.4 Strategies to Reduce the Frequency of Disease
14.4.1 Disease Prevention
14.4.2 Disease Control
14.4.3 Disease Eradication
14.4.3.1 Test and Removal versus Herd Depopulation
14.4.3.2 Necessary Conditions for Eradication
References
Answers to Follow-Up Questions
Glossary
Index