U.S. Department of Justice National Institute of Corrections HOW TO COLLECT AND ANALYZE DATA: A Manual for Sheriffs and Jail Administrators U.S. Department of Justice National Institute of Corrections 320 First Street, NW Washington, DC 20534 Morris L. Thigpen Director Thomas J. Beauclair Deputy Director Virginia Hutchinson Chief, Jails Division Vicci Persons Project Manager National Institute of Corrections http://www.nicic.org HOW TO COLLECT AND ANALYZE DATA: A Manual for Sheriffs and Jail Administrators 3rd edition Gail Elias July 2007 NIC Accession Number 021826 This publication was funded by the National Institute of Corrections, U.S. Department of Justice. Points of view or opinions stated in this publication are those of the author and do not necessarily represent the official position or policies of the U.S. Department of Justice. Copyright © 2007, Voorhis Associates, Inc. The National Institute of Corrections reserves the right to reproduce, publish, translate, or otherwise use and to authorize others to publish and use all or any part of the copyrighted material contained in this publication. Table of Contents FOREWORD . vii PREFACE . ix ACKNOWLEDGMENTS . xi CHAPTER 1: INTRODUCTION . 1-1 The Situation . 1-3 Traditional Resources Have Failed To Help . 1-4 Resource 1: Introductory Statistics Courses . 1-4 Resource 2: Information Systems Seminars . 1-4 Resource 3: Research Methods . 1-5 Additional Resources . 1-5 CHAPTER 2: GOOD MANAGEMENT REQUIRES GOOD INFORMATION . 2-1 What Is Management? . 2-3 Ways To Get the Facts . 2-4 What Can You Do With Data? . 2-4 Example 1: Better Budgeting and Allocation of Funds . 2-4 Example 2: More Effective Deployment of Staff . 2-5 Conclusion . 2-6 CHAPTER 3: INFORMATION THAT SHOULD BE COLLECTED . 3-1 Writing Good Problem Statements . 3-3 Identifying Data Elements From Problem Statements . 3-4 A Catalog of Correctional Data Elements . 3-5 Inmate Population Data Elements . 3-6 Inmate Profile Data Elements . 3-7 Operational Data Elements . 3-10 Criminal Justice System Performance Data Elements . 3-12 A Word About Collecting Data in Other Agencies . 3-14 Conclusion . 3-14 iii CHAPTER 4: PREPARING FOR THE DATA COLLECTION . 4-1 Data Collection Skills . 4-3 Where To Find the Skills You Need . 4-4 Working With People From Outside the System . 4-5 Conclusion . 4-6 CHAPTER 5: HOW TO LOCATE AND CAPTURE INFORMATION . 5-1 Jail Information Sources . 5-3 Logs and Forms . 5-5 Summary . 5-7 The Problem With Data Sources—and Some Solutions . 5-8 Problem 1: Data Elements Are Scattered . 5-8 Problem 2: Data Is Missing . 5-8 Problem 3: Information on the Form Is Wrong . 5-9 Problem 4: Data Elements Are Poorly Defined . 5-9 Problem 5: The Handwriting Is Illegible . 5-10 Problem 6: No One Keeps Data for the Whole System . 5-10 Setting Up an Information System for the Jail . 5-10 Elements of the System . 5-10 System Startup . 5-10 Special Issue Data Collections . 5-18 Designing Special Data Collection Forms and Code Books . 5-19 Conclusion . 5-24 CHAPTER 6: HOW TO PUT IT ALL TOGETHER . 6-1 Doing the Data Collection . 6-3 Determine an Overall Strategy . 6-3 Determine How Much Data To Collect . 6-4 Coding . 6-7 Rules for Coding Data . 6-7 Coding in an Automated System . 6-8 Gather Your Data Collection Supplies . 6-10 Begin . 6-10 Automation Issues . 6-12 Conclusion . 6-12 CHAPTER 7: HOW TO ANALYZE INFORMATION . 7-1 What is Statistics? . 7-4 Statistically Significant Differences . 7-4 Probability . 7-4 Normal (Bell-Shaped) Distribution . 7-5 Statistical Results . 7-6 Types of Statistics . 7-6 Descriptive Statistics . 7-6 Statistics for Examining Differences Between Groups . 7-11 Statistics To Examine the Relationship Between Data Elements . 7-13 Statistical Sins . 7-15 Sin 1: How Could the Results Be Wrong if the Calculations Were Perfect? . 7-15 iv HOW TO COLLECT AND ANALYZE DATA Sin 2: What Is the Real Average? . 7-16 Sin 3: What Is Missing From This Picture? . 7-17 Sin 4: So What if It Is Statistically Significant? . 7-17 Sin 5: If A, Then B? . 7-17 Sin 6: What Is Wrong With This Picture? . 7-18 Conclusion . 7-18 CHAPTER 8: HOW TO INTERPRET INFORMATION . 8-1 Case Study 1: The Friday Night Blues . 8-4 Before Going on to Case Study 2 . 8-15 Case Study 2: The Alternative Answer . 8-15 Conclusion . 8-27 CHAPTER 9: SHARING INFORMATION WITH OTHERS . 9-1 Why Pictures Are Worth a Thousand Numbers . 9-4 Methods for Displaying Data . 9-4 Tables . 9-4 Bar Charts . 9-5 Pie Charts . 9-6 Line Graphs . 9-6 Guidelines for Good Graphics . 9-7 Rule 1: Know Your Limitations . 9-7 Rule 2: Make the Graphic Illustrate the Most Important Information . 9-7 Rule 2a: Keep It Simple . 9-7 Rule 3: Determine the Best Medium for Sharing the Information . 9-9 Rule 4: Decide What Scale Will Best Display the Data . 9-10 Rule 5: Consider Who the Audience Is . 9-10 Rule 6: Make the Graphic Pleasing to the Eye . 9-11 Rule 7: Resist the Temptation to Save Money by Putting Everything on One Page, Transparency, or Slide . 9-11 Conclusion . 9-11 CHAPTER 10: GETTING THE MOST FROM YOUR INFORMATION SYSTEM . 10-1 What This Chapter Is—and Is Not—About . 10-3 A Short Course in Computers . 10-4 Overview of Computer Elements . 10-4 The Central Computer . 10-4 Peripherals . 10-5 Communication Devices . 10-5 Overview of Software . 10-5 Applications Software . 10-6 A Last Word on Hardware and Software . 10-7 Getting the Most Out of a Database . 10-7 What To Do Before Buying or Upgrading a Computer . 10-8 Determine the Purpose of the Information System . 10-8 Define Your Needs . 10-9 System Expectations and Guidelines . 10-12 The User Manages the System . 10-12 CONTENTS v The System Avoids Duplication of Effort . 10-12 The System Is Reliable . 10-12 The System Has a Safety Net . 10-12 Match the Right Application to the Task . 10-12 Know How the System Handles Updated Information . 10-12 Format Flexibility . 10-13 Determine Internal Checks . 10-13 User Guidelines . 10-13 Explore the System . 10-13 Practice Analysis . 10-13 APPENDIX A: A GLOSSARY OF STATISTICAL TERMS FOR NON-STATISTICIANS . A-1 APPENDIX B: ANNOTATED BIBLIOGRAPHY . B-1 Resources for the Criminal Justice System . B-3 Other Resources . B-5 APPENDIX C: MANUAL DATA COLLECTION PROCEDURES AND SAMPLE FORMS . C-1 Elements of the System . C-3 System Startup . C-4 APPENDIX D: INMATE PROFILE DATA COLLECTION . D-1 Data Collection Form . D-3 Inmate Profile Data Collection Code Book . D-4 APPENDIX E: INCIDENT DATA CODE BOOK . E-1 APPENDIX F: TRANSPORT DATA COLLECTION . F-1 APPENDIX G: TABLES FOR DETERMINING SAMPLE SIZE . G-1 APPENDIX H: SIMPLE RANDOM SAMPLING . H-1 APPENDIX I: CALCULATING THE STANDARD DEVIATION . I-1.