Planning and Executing Credible Experiments

Planning and Executing Credible Experiments
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Covers experiment planning, execution, analysis, and reporting This single-source resource guides readers in planning and conducting credible experiments for engineering, science, industrial processes, agriculture, and business. The text takes experimenters all the way through conducting a high-impact experiment, from initial conception, through execution of the experiment, to a defensible final report. It prepares the reader to anticipate the choices faced during each stage.  Filled with real-world examples from engineering science and industry, Planning and Executing Credible Experiments: A Guidebook for Engineering, Science, Industrial Processes, Agriculture, and Business offers chapters that challenge experimenters at each stage of planning and execution and emphasizes uncertainty analysis as a design tool in addition to its role for reporting results. Tested over decades at Stanford University and internationally, the text employs two powerful, free, open-source software tools: GOSSET to optimize experiment design, and R for statistical computing and graphics. A website accompanies the text, providing additional resources and software downloads. A comprehensive guide to experiment planning, execution, and analysis Leads from initial conception, through the experiment’s launch, to final report Prepares the reader to anticipate the choices faced throughout an experiment Hones the motivating question Employs principles and techniques from Design of Experiments (DoE) Selects experiment designs to obtain the most information from fewer experimental runs Offers chapters that propose questions that an experimenter will need to ask and answer during each stage of planning and execution Demonstrates how uncertainty analysis guides and strengthens each stage Includes examples from real-life industrial experiments Accompanied by a website hosting open-source software Planning and Executing Credible Experiments is an excellent resource for graduates and senior undergraduates—as well as professionals—across a wide variety of engineering disciplines.

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Robert J. Moffat. Planning and Executing Credible Experiments

Table of Contents

List of Tables

List of Illustrations

Guide

Pages

Planning and Executing Credible Experiments. A Guidebook for Engineering, Science, Industrial Processes, Agriculture, and Business

About the Authors

Preface

Audience

Accompanying Material

Recommended Companion Texts

How Is This Book Used for Teaching?

Acknowledgments

About the Companion Website

1 Choosing Credibility

1.1 The Responsibility of an Experimentalist

1.2 Losses of Credibility

1.3 Recovering Credibility

1.4 Starting with a Sharp Axe

1.5 A Systems View of Experimental Work

1.6 In Defense of Being a Generalist

Panel 1.1 The Bundt Cake Story

The Moral of This Story?

References

Homework

Notes

2 The Nature of Experimental Work

2.1 Tested Guide of Strategy and Tactics

2.2 What Can Be Measured and What Cannot?

2.2.1 Examples Not Measurable

2.2.2 Shapes

2.2.3 Measurable by the Human Sensory System

2.2.4 Identifying and Selecting Measurable Factors

2.2.5 Intrusive Measurements

2.3 Beware Measuring Without Understanding: Warnings from History

2.4 How Does Experimental Work Differ from Theory and Analysis?

2.4.1 Logical Mode

2.4.2 Persistence

2.4.3 Resolution

2.4.4 Dimensionality

2.4.5 Similarity and Dimensional Analysis

2.4.6 Listening to Our Theoretician Compatriots

Panel 2.1 Positive Consequences of the Reproducibility Crisis

Panel 2.2 Selected Invitations to Experimental Research, Insights from Theoreticians

Better Invitation than a Nobel Prize

Einstein's Theory Always Invites Tests

Observations of a Popular Theoretical Physics Field

Another Invitation from Feynman

Extra Invitations to Experiments

Panel 2.3 Prepublishing Your Experiment Plan

2.4.7 Surveys and Polls

2.5 Uncertainty

2.6 Uncertainty Analysis

References

Homework

Notes

3 An Overview of Experiment Planning

3.1 Steps in an Experimental Plan

3.2 Iteration and Refinement

3.3 Risk Assessment/Risk Abatement

3.4 Questions to Guide Planning of an Experiment

Homework

4 Identifying the Motivating Question

4.1 The Prime Need

Panel 4.1 There's a Hole in My Bucket

4.2 An Anchor and a Sieve

4.3 Identifying the Motivating Question Clarifies Thinking

4.3.1 Getting Started

4.3.2 Probe and Focus

4.4 Three Levels of Questions

4.5 Strong Inference

4.6 Agree on the Form of an Acceptable Answer

4.7 Specify the Allowable Uncertainty

4.8 Final Closure

Reference

Homework

Notes

5 Choosing the Approach. 5.1 Laying Groundwork

5.2 Experiment Classifications

5.2.1 Exploratory

5.2.2 Identifying the Important Variables

5.2.3 Demonstration of System Performance

5.2.4 Testing a Hypothesis

5.2.5 Developing Constants for Predetermined Models

5.2.6 Custody Transfer and System Performance Certification Tests

5.2.7 Quality‐Assurance Tests

5.2.8 Summary

5.3 Real or Simplified Conditions?

5.4 Single‐Sample or Multiple‐Sample?

Panel 5.1 A Brief Summary of “Dissertation upon Roast Pig” (with Thanks and Apologies to Charles Lamb [1775–1834])

Panel 5.2 Consider a Spherical Cow

5.5 Statistical or Parametric Experiment Design?

5.6 Supportive or Refutative?

5.7 The Bottom Line

References

Homework

Notes

6 Mapping for Safety, Operation, and Results. 6.1 Construct Multiple Maps to Illustrate and Guide Experiment Plan

6.2 Mapping Prior Work and Proposed Work

6.3 Mapping the Operable Domain of an Apparatus

6.4 Mapping in Operator's Coordinates

6.5 Mapping the Response Surface

6.5.1 Options for Organizing a Table

6.5.2 Options for Presenting the Response on a Scatter‐Plot‐Type Graph

Homework

7 Refreshing Statistics

7.1 Reviving Key Terms to Quantify Uncertainty. 7.1.1 Population

7.1.2 Sample

7.1.3 Central Value

7.1.4 Mean, μ or Y

7.1.5 Residual

7.1.6 Variance, σ2 or S2

7.1.7 Degrees of Freedom, Df

7.1.8 Standard Deviation, σY or SY

7.1.9 Uncertainty of the Mean, δμ

7.1.10 Chi‐Squared, χ2

7.1.11 p‐Value

7.1.12 Null Hypothesis

7.1.13 F‐value of Fisher Statistic

7.2 The Data Distribution Most Commonly Encountered. The Normal Distribution for Samples of Infinite Size

7.3 Account for Small Samples: The t‐Distribution

7.4 Construct Simple Models by Computer to Explain the Data

7.4.1 Basic Statistical Analysis of Quantitative Data

7.4.2 Model Data Containing Categorical and Quantitative Factors

7.4.3 Display Data Fit to One Categorical Factor and One Quantitative Factor

7.4.4 Quantify How Each Factor Accounts for Variation in the Data

7.5 Gain Confidence and Skill at Statistical Modeling Via the R Language

7.5.1 Model and Plot Results of a Single Variable Using the Example Data diceshoe.csv

7.5.2 Evaluate Alternative Models of the Example Data hiloy.csv (Sections 7.5.3 Through 7.5.8) 7.5.2.1 Inspect the Data

7.5.3 Grand Mean

7.5.4 Model by Groups: Group‐Wise Mean

7.5.5 Model by a Quantitative Factor

7.5.6 Model by Multiple Quantitative Factors

7.5.7 Allow Factors to Interact (So Each Group Gets Its Own Slope)

7.5.8 Include Polynomial Factors (a Statistical Linear Model Can Be Curved)

7.6 Report Uncertainty

7.7 Decrease Uncertainty (Improve Credibility) by Isolating Distinct Groups

7.8 Original Data, Summary, and R

References

Homework

Notes

8 Exploring Statistical Design of Experiments. 8.1 Always Seeking Wiser Strategies

8.2 Evolving from Novice Experiment Design

8.3 Two‐Level and Three‐Level Factorial Experiment Plans

8.4 A Three‐Level, Three‐Factor Design

8.5 The Plackett–Burman 12‐Run Screening Design

8.6 Details About Analysis of Statistically Designed Experiments

8.6.1 Model Main Factors to Original Raw Data

8.6.2 Model Main Factors to Original Data Around Center of Each Factor

8.6.3 Model Including All Interaction Terms

8.6.4 Model Including Only Dominant Interaction Terms

8.6.5 Model Including Dominant Interaction Term Plus Quadratic Term

8.6.6 Model All Factors of Example 2, Centering Each Quantitative Factor

8.6.7 Refine Model of Example 2 Including Only Dominant Terms

8.7 Retrospect of Statistical Design Examples

8.8 Philosophy of Statistical Design

8.9 Statistical Design for Conditions That Challenge Factorial Designs

8.10 A Highly Recommended Tool for Statistical Design of Experiments

8.11 More Tools for Statistical Design of Experiments

8.12 Conclusion

Further Reading

Homework

Notes

9 Selecting the Data Points

9.1 The Three Categories of Data

9.1.1 The Output Data

9.1.2 Peripheral Data

9.1.3 Backup Data

9.1.4 Other Data You May Wish to Acquire

9.2 Populating the Operating Volume. 9.2.1 Locating the Data Points Within the Operating Volume

9.2.2 Estimating the Topography of the Response Surface

9.3 Example from Velocimetry

9.3.1 Sharpen Our Approach

9.3.2 Lessons Learned from Velocimetry Example

9.4 Organize the Data. 9.4.1 Keep a Laboratory Notebook

9.4.2 Plan for Data Security

9.4.3 Decide Data Format

9.4.4 Overview Data Guidelines

9.4.5 Reasoning Through Data Guidelines

9.5 Strategies to Select Next Data Points

9.5.1 Overview of Option 1: Default Strategy with Intensive Experimenter Involvement

9.5.1.1 Choosing the Data Trajectory

9.5.1.2 The Default Strategy: Be Bold

9.5.1.2.1 Halve Rather than Nibble

9.5.1.3 Anticipate, Check, Course Correct

9.5.1.4 Other Aspects to Keep in Mind

9.5.1.5 Endpoints

9.5.2 Reintroducing Gosset

9.5.3 Practice Gosset Examples (from Gosset User Manual)

9.6 Demonstrate Gosset for Selecting Data

9.6.1 Status Quo of Experiment Planning and Execution (Prior to Selecting More Samples)

9.6.1.1 Specified Motivating Question

9.6.1.2 Identified Pertinent Candidate Factors

9.6.1.3 Selected Initial Sample Points Using Plackett–Burman

9.6.1.4 Executed the First 12 Runs at the PB Sample Conditions

9.6.1.5 Analyzed Results. Identified Dominant First‐Order Factors. Estimated First‐Order Uncertainties of Factors

9.6.1.6 Generated Draft Predictive Equation

9.6.2 Use Gosset to Select Additional Data Samples

9.6.2.1 Example Gosset Session: User Input to Select Next Points

9.6.2.2 Example Gosset Session: How We Chose User Input

9.6.2.3 Example Gosset Session: User Input Along with Gosset Output

9.6.2.4 Example Gosset Session: Convert the Gosset Design to Operator Values

9.6.2.5 Results of Example Gosset Session: Operator Plots of Total Experiment Plan

9.6.2.6 Execute Stage Two of the Experiment Plan: User Plus Gosset Sample Points

9.7 Use Gosset to Analyze Results

9.8 Other Options and Features of Gosset

9.9 Using Gosset to Find Local Extrema in a Function of Several Variables

9.10 Summary

Further Reading

Homework

10. Analyzing Measurement Uncertainty. 10.1 Clarifying Uncertainty Analysis

10.1.1 Distinguish Error and Uncertainty

10.1.1.1 Single‐Sample vs. Multiple‐Sample

10.1.2 Uncertainty as a Diagnostic Tool

10.1.2.1 What Can Uncertainty Analysis Tell You?

10.1.2.2 What Is Uncertainty Analysis Good For?

10.1.2.3 Uncertainty Analysis Can Redirect a Poorly Conceived Experiment

10.1.2.4 Uncertainty Analysis Improves the Quality of Your Work

10.1.2.5 Slow Sampling and “Randomness”

10.1.2.6 Uncertainty Analysis Makes Results Believable

10.1.3 Uncertainty Analysis Aids Management Decision‐Making

10.1.3.1 Management's Task: Dealing with Warranty Issues

10.1.4 The Design Group's Task: Setting Tolerances on Performance Test Repeatability

10.1.5 The Performance Test Group's Task: Setting the Tolerances on Measurements

10.2 Definitions

10.2.1 True Value

10.2.2 Corrected Value

10.2.3 Data Reduction Program

10.2.4 Accuracy

10.2.5 Error

10.2.6 XXXX Error

10.2.7 Fixed Error

10.2.8 Residual Fixed Error

10.2.9 Random Error

10.2.10 Variable (but Deterministic) Error

10.2.11 Uncertainty

10.2.12 Odds

10.2.13 Absolute Uncertainty

10.2.14 Relative Uncertainty

10.3 The Sources and Types of Errors

10.3.1 Types of Errors: Fixed, Random, and Variable

10.3.2 Sources of Errors: The Measurement Chain

10.3.2.1 The Undisturbed Value

10.3.2.2 The Available Value

10.3.2.3 The Achieved Value

10.3.2.4 The Observed Value

10.3.2.5 The Corrected Value

10.3.3 Specifying the True Value

10.3.3.1 If the Achieved Value Is Taken as the True Value

10.3.3.2 If the Available Value Is Taken as the True Value

10.3.3.3 If the Undisturbed Value Is Taken as the True Value

10.3.3.4 If the Mixed Mean Gas Temperature Is Taken as the True Value

10.3.4 The Role of the End User

10.3.4.1 The End‐Use Equations Implicitly Define the True Value

10.3.5 Calibration

10.4 The Basic Mathematics

10.4.1 The RSS Combination

10.4.2 The Fixed Error in a Measurement

10.4.3 The Random Error in a Measurement

10.4.4 The Uncertainty in a Measurement

10.4.5 The Uncertainty in a Calculated Result

10.4.5.1 The Relative Uncertainty in a Result

10.5 Automating the Uncertainty Analysis

10.5.1 The Mathematical Basis

10.5.2 Example of Uncertainty Analysis by Spreadsheet

10.6 Single‐Sample Uncertainty Analysis

10.6.1 Assembling the Necessary Inputs

10.6.2 Calculating the Uncertainty in the Result

10.6.3 The Three Levels of Uncertainty: Zeroth‐, First‐, and Nth‐Order

10.6.3.1 Zeroth‐Order Replication

10.6.3.2 First‐Order Replication

10.6.3.3 Nth‐Order Replication

10.6.4 Fractional‐Order Replication for Special Cases

10.6.5 Summary of Single‐Sample Uncertainty Levels. 10.6.5.1 Zeroth‐Order

10.6.5.2 First‐Order

10.6.5.3 Nth‐Order

References

Further Reading

Homework

11 Using Uncertainty Analysis in Planning and Execution

11.1 Using Uncertainty Analysis in Planning

11.1.1 The Physical Situation and Energy Analysis

11.1.2 The Steady‐State Method

11.1.3 The Transient Method

11.1.4 Reflecting on Assumptions Made During DRE Derivations

11.2 Perform Uncertainty Analysis on the DREs. 11.2.1 Uncertainty Analysis: General Form

11.2.2 Uncertainty Analysis of the Steady‐State Method

11.2.3 Uncertainty Analysis – Transient Method

11.2.4 Compare the Results of Uncertainty Analysis of the Methods

Planning Decisions

11.2.5 What Does the Calculated Uncertainty Interval Mean?

11.2.6 Cross‐Checking the Experiment

11.2.7 Conclusions

11.3 Using Uncertainty Analysis in Selecting Instruments

11.4 Using Uncertainty Analysis in Debugging an Experiment

11.4.1 Handling Overall Scatter

11.4.2 Sources of Scatter

11.4.3 Advancing Toward Calibration

11.4.4 Selecting Thresholds

11.4.5 Iterating Analysis

11.4.6 Rechecking Situational Uncertainty

11.5 Reporting the Uncertainties in an Experiment

11.5.1 Progress in Uncertainty Reporting

11.6 Multiple‐Sample Uncertainty Analysis. 11.6.1 Revisiting Single‐Sample and Multiple‐Sample Uncertainty Analysis

11.6.2 Examples of Multiple‐Sample Uncertainty Analysis

11.6.3 Fixed Error and Random Error

11.7 Coordinate with Uncertainty Analysis Standards

11.7.1 Describing Fixed and Random Errors in a Measurement

11.7.2 The Bias Limit

11.7.2.1 Fossilization

11.7.2.2 Bias Limits

11.7.3 The Precision Index

11.7.4 The Number of Degrees of Freedom

11.8 Describing the Overall Uncertainty in a Single Measurement

11.8.1 Adjusting for a Single Measurement

11.8.2 Describing the Overall Uncertainty in a Result

11.8.3 Adding the Overall Uncertainty to Predictive Models

11.9 Additional Statistical Tools and Elements

11.9.1 Pooled Variance

11.9.1.1 Student's t‐Distribution – Pooled Examples

11.9.2 Estimating the Standard Deviation of a Population from the Standard Deviation of a Small Sample: The Chi‐Squared χ2 Distribution

References

Homework

12 Debugging an Experiment, Shakedown, and Validation. 12.1 Introduction

12.2 Classes of Error

12.3 Using Time‐Series Analysis in Debugging

12.4 Examples

12.4.1 Gas Temperature Measurement

12.4.2 Calibration of a Strain Gauge

12.4.3 Lessons Learned from Examples

12.5 Process Unsteadiness

12.6 The Effect of Time‐Constant Mismatching

12.7 Using Uncertainty Analysis in Debugging an Experiment

12.7.1 Calibration and Repeatability

12.7.2 Stability and Baselining

12.8 Debugging the Experiment via the Data Interpretation Program

12.8.1 Debug the Experiment via the DIP

12.8.2 Debug the Interface of the DIP

12.8.3 Debug Routines in the DIP

12.9 Situational Uncertainty

13 Trimming Uncertainty. 13.1 Focusing on the Goal

13.2 A Mlotivating Question for Industrial Production

13.2.1 Agreed Motivating Questions for Industrial Example

13.2.2 Quick Answers to Motivating Questions

13.2.3 Challenge: Precheck Analysis and Answers

13.3 Plackett–Burman 12‐Run Results and Motivating Question #3

13.4 PB 12‐Run Results and Motivating Question #1

13.4.1 Building a Predictive Model Equation from R‐Language Linear Model

13.4.2 Parsing the Dual Predictive Model Equation

13.4.3 Uncertainty of the Intercept in the Dual Predictive Model Equation

13.4.4 Mapping an Answer to Motivating Question #1

13.4.5 Tentative Answers to Motivating Question #1

13.5 Uncertainty Analysis of Dual Predictive Model and Motivating Question #2

13.5.1 Uncertainty of the Constant in the Dual Predictive Model Equation

13.5.2 Uncertainty of Other Factors in the Dual Predictive Model Equation

13.5.3 Include All Coefficient Uncertainties in the Dual Predictive Model Equation

13.5.4 Overall Uncertainty from All Factors in the Predictive Model Equation

13.5.5 Improved Tentative Answers to Motivating Questions, Including Uncertainties

13.5.6 Search for Improved Predictive Models

13.6 The PB 12‐Run Results and Individual Machine Models

13.6.1 Individual Machine Predictive Model Equations

13.6.2 Uncertainty of the Intercept in the Individual Predictive Model Equations

13.6.3 Uncertainty of the Constant in the Individual Predictive Model Equations

13.6.4 Uncertainty of Other Factors in the Individual Predictive Model Equation

13.6.4.1 Uncertainties of Machine 1

13.6.4.2 Uncertainties of Machine 2

13.6.4.3 Including Instrument and Measurement Uncertainties

13.6.5 Include All Coefficient Uncertainties in the Individual Predictive Model Equations

13.6.6 Overall Uncertainty from All Factors in the Individual Predictive Model Equations

13.6.7 Quick Overview of Individual Machine Performance Over the Operating Map

13.7 Final Answers to All Motivating Questions for the PB Example Experiment

13.7.1 Answers to Motivating Question #1

13.7.2 Answers to Motivating Question #2

13.7.3 Answers to Motivating Question #3 (Expanded from Section 13.3)

13.7.4 Answers to Motivating Question #4

13.7.5 Other Recommendations (to Our Client)

13.8 Conclusions

Homework

Notes

14 Documenting the Experiment : Report Writing

14.1 The Logbook

14.2 Report Writing

14.2.1 Organization of the Reports

14.2.2 Who Reads What?

14.2.3 Picking a Viewpoint

14.2.4 What Goes Where?

14.2.4.1 What Goes in the Abstract?

14.2.4.2 What Goes in the Foreword?

14.2.4.3 What Goes in the Objective?

14.2.4.4 What Goes in the Results and Conclusions?

14.2.4.5 What Goes in the Discussion?

14.2.4.6 References

14.2.4.7 Figures

14.2.4.8 Tables

14.2.4.9 Appendices

14.2.5 The Mechanics of Report Writing

14.2.6 Clear Language Versus “JARGON”

Panel 14.1 The Turbo‐Encabulator

14.2.7 “Gobbledygook”: Structural Jargon

Panel 14.2 U.S. Code, Title 18, No. 793 *

14.2.8 Quantitative Writing

14.2.8.1 Substantive Versus Descriptive Writing

Panel 14.3 The Descriptive Bank Statement

Abstract

14.2.8.2 Zero‐Information Statements

14.2.8.3 Change

14.3 International Organization for Standardization, ISO 9000 and other Standards

14.4 Never Forget. Always Remember

Notes

Appendix A Distributing Variation and Pooled Variance. A.1 Inescapable Distributions. A.1.1 The Normal Distribution for Samples of Infinite Size

A.1.2 Adjust Normal Distributions with Few Data: The Student’s t‐Distribution

A.2 Other Common Distributions

A.2.1.1 Discrete Distributions

A.2.1.2 Continuous Distributions

A.3 Pooled Variance (Advanced Topic)

Note

Appendix B Illustrative Tables for Statistical Design. B.1 Useful Tables for Statistical Design of Experiments. B.1.1 Ready‐made Ordering for Randomized Trials

B.1.2 Exhausting Sets of Two‐Level Factorial Designs (≤ Five Factors)

B.2 The Plackett–Burman (PB) Screening Designs

Appendix C Hand Analysis of Two‐Level Factorial Designs

C.1 The General Two‐Level Factorial Design

C.2 Estimating the Significance of the Apparent Factor Effects

C.3 Hand Analysis of a Plackett–Burman (PB) 12‐Run Design

C.4 Illustrative Practice Example for the PB 12‐Run Pattern

C.4.1 Assignment: Find Factor Effects and the Linear Coefficients Absent Noise

C.4.2 Assignment: Find Factor Effects and the Linear Coefficients with Noise

C.5 Answer Key: Compare Your Hand Calculations. C.5.1 Expected Results Absent Noise (compare C.4.1)

C.5.2 Expected Results with Random Gaussian Noise (cf. C.4.2)

C.6 Equations for Hand Calculations

Appendix D Free Recommended Software: Obtain Recommended Free, Open‐Source Software for Your Computer. D.1 Instructions to Obtain the R Language for Statistics

D.2 Instructions to Obtain LibreOffice

D.3 Instructions to Obtain Gosset

D.4 Possible Use of RStudio

Index. a

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Robert J. Moffat

.....

NASA provides a good example of the interdependence of theory and experiment. The National Advisory Council on Aeronautics (NACA) was the precursor of NASA; “Aeronautics” is the first A of NASA. As airplane designs rapidly advanced during the 1900s, NASA deliberately adopted a four‐pronged approach: theory, scale‐model testing (wind‐tunnel experiments), full‐scale testing (in‐flight experiments), and numerical simulation (computational models verified by experiment). Each of the first three prongs have always been essential (Baals and Corliss 1981). Since the 1980s, numerical simulation has aided theory. Theory and experiment need each other. Since our numerical colleagues often refer to their “numerical experiments,” we do advocate an appropriate way to report the uncertainties of their results, just as we experimentalists do.

The science of fluid flow remains important, as another quote (from a personal letter) from Feynman makes clear:

.....

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