National Academies Press: OpenBook
Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
×

Ensuring Safe Food From Production to Consumption

Committee to Ensure Safe Food from Production to Consumption

INSTITUTE OF MEDICINE

NATIONAL RESEARCH COUNCIL

NATIONAL ACADEMY PRESS
Washington, D.C.
1998

Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
×

NATIONAL ACADEMY PRESS
2101 Constitution Avenue, N.W. Washington, DC 20418

NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.

The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences.

The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering.

The Institute of Medicine was established in 1970 by the National Academy of Sciences to enlist distinguished members of the appropriate professions in the examination of policy matters pertaining to the health of the public. In this, the Institute acts under both the Academy's 1863 congressional charter responsibility to be an adviser to the federal government and its own initiative in identifying issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine.

The National Research Council was organized by the National Academy of Sciences in 1916 to link the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. William A. Wulf are chairman and vice-chairman, respectively, of the National Research Council.

This material is based upon work supported by the U.S. Department of Agriculture, Agricultural Research Service, under Agreement No. 59-0790-8-013. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author and do not necessarily reflect the view of the U.S. Department of Agriculture.

Library of Congress Cataloging-in-Publication Data 98-86932 International Standard Book No: 0-309-06559-3

This report is available for sale from the
National Academy Press,
2101 Constitution Avenue, N.W., Box 285, Washington, DC 20055, Call (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area), or visit the NAP's on-line bookstore at http://www.nap.edu.

©1998 by the National Academy of Sciences. All rights reserved.

Printed in the United States of America

Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
×

COMMITTEE TO ENSURE SAFE FOOD FROM PRODUCTION TO CONSUMPTION

JOHN C. BAILAR III* (Chair),

Department of Health Studies, The University of Chicago, Illinois

CAROLE A. BISOGNI,

Division of Nutritional Sciences, Cornell University, Ithaca, New York

DAVID L. CALL, Retired,

College of Agriculture and Life Sciences, Cornell University, Ithaca, New York

MARSHA N. COHEN,

Hastings College of the Law, University of California, San Francisco

MICHAEL P. DOYLE,

Center for Food Safety and Quality Enhancement, University of Georgia, Griffin

DELIA A. HAMMOCK,

Good Housekeeping Institute, New York

LONNIE J. KING,

College of Veterinary Medicine, Michigan State University, East Lansing

GILBERT A. LEVEILLE,

Leveille Associates, Denville, New Jersey

RICHARD A. MERRILL,*

University of Virginia School of Law, Charlottesville, Virginia

SANFORD A. MILLER,

Graduate School of Biomedical Sciences, University of Texas Health Science Center, San Antonio

HARLEY W. MOON,

Veterinary Medical Research Institute, Iowa State University, Ames

MICHAEL T. OSTERHOLM,

Minnesota Department of Health, Minneapolis

THOMAS D. TRAUTMAN,

General Mills, Minneapolis, Minnesota

Staff

ALLISON A. YATES, Study Director

CHARLOTTE KIRK BAER, Senior Program Officer

SANDRA A. SCHLICKER, Senior Program Officer

ELISABETH REESE, Research Associate

KATHERINE J. GORTON, Policy Intern

GAIL E. SPEARS, Administrative Assistant

SHIRLEY B. THATCHER, Administrative Assistant

GERALDINE KENNEDO, Project Assistant

MELINDA SIMONS, Project Assistant

*  

Member, Institute of Medicine.

  

Member, National Academy of Sciences.

Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
×

FOOD SAFETY OVERSIGHT COMMISSION

DONALD KENNEDY (Chair), *

Institute for International Studies, Stanford University, California

DALE E. BAUMAN,

Cornell University, Ithaca, New York

FERGUS M. CLYDESDALE,

University of Massachusetts at Amherst

JOHANNA T. DWYER,

Tufts Medical School and School of Nutrition Science and Policy, New England Medical Center, Boston, Massachusetts

JOHN W. ERDMAN, Jr.,

College of Agriculture, University of Illinois at Urbana-Champaign

CUTBERTO GARZA,

Cornell University, Ithaca, New York

GEORGE R. HALLBERG,

The Cadmus Group, Inc., Waltham, Massachusetts

JOHN W. SUTTIE,

University of Wisconsin-Madison

BAILUS WALKER, Jr.,*

Howard University Cancer Center, Washington, DC

Staff

PAUL GILMAN, Executive Director,

Board on Agriculture

KAREN HEIN, Executive Officer,

Institute of Medicine

MICHAEL J. PHILLIPS, Director,

Board on Agriculture

ALLISON A. YATES, Director,

Food and Nutrition Board

*  

Member, Institute of Medicine.

  

Member, National Academy of Sciences.

Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
×

Preface

Protecting the food supply from harmful agents and thus promoting the public health is an important activity of government. The current system for food safety in the United States is a complex and multi-layered activity that depends on multiple players that include the federal government, state governments, local governments, universities, the news media, and, of course, the public itself, both as preparers and handlers of food and as consumers. These varied roles which each segment plays in food safety, with their many complexities and charges, must be integrated within the equally complex and changing system of the food supply from production to final consumption. Though the federal roles of guidance, research, surveillance, enforcement, and education are extremely important, they represent only one part of the food safety system.

Given the size and complexity of this multi-faceted system, it is not unexpected that new information and new concerns often emerge. Many are due to advances in science or to changes in food production and consumption patterns. The system itself must then change if it is to maintain effective vigilance over the safety of the food supply. Congress has acted to strengthen the federal role as the primary agent for integration of activities related to food safety. Many components of the federal food safety system determined by Congress have been relatively unchanged over the last few decades, and concerns have come forward that major changes may be required.

At the request of Congress, and in light of the emerging food safety concerns and many recent proposals recommending change, the Agricultural Research Service of the United States Department of Agriculture asked the National Academy of Sciences (NAS) in late 1997 to 1) determine the scientific

Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
×

basis of an effective food safety system, 2) assess the effectiveness of the current food safety system in the United States, 3) identify scientific needs and gaps within the current system, and 4) provide recommendations on scientific and organizational changes in federal food safety activity needed to ensure an effective science-based food safety system.

The Committee to Ensure Safe Food from Production to Consumption was formed by the Institute of Medicine (IOM) and National Research Council (NRC) to do the evaluation in response to this request. The committee reviewed mechanisms now in place at the federal level to ensure safe food, assessed the extent to which they are effective in addressing food safety issues from production to consumption, and developed recommendations about changes needed to move toward a more effective food safety system. This volume reports the deliberations, conclusions, and recommendations of the committee.

The IOM and the NRC also formed an oversight commission composed of members from the Food and Nutrition Board, the Board on Agriculture, and the Board on Environmental Studies and Toxicology of the Commission on Life Sciences. The chair, Donald Kennedy, is a member of both IOM and of NAS. The role of the Commission was to nominate a committee whose expertise would be appropriately balanced for a study of this scope and complexity. The multidisciplinary group included experts in public health, epidemiology, food science, food microbiology, production agriculture, veterinary medicine, food technology, food regulatory law, consumer protection, consumer education, and media communications. In addition, five members of the 13 member committee held previous positions in federal agencies involved in food safety, three were from the food industry, and two from the agriculture/aquaculture industry. And, of course, all committee members are frequent consumers of food (see Appendix G for biographical sketches of each committee member).

The committee held three meetings during its short period of deliberations. The first meeting, held March 23 to 25, 1998, included an open meeting to hear from the federal agencies most involved with food safety and from Dr. Ed Knipling, Associate Administrator of ARS/USDA who served as the project officer for the study. Representatives from each agency were asked to discuss the mission of their agency and its involvement in regulatory efforts, and to provide the agency budget for key activities related to food safety (see Appendix E).

The second meeting, held April 28 to May 1, 1998, was held in conjunction with an open meeting to which individuals representing many of the major organizations with interests related to food safety presented their responses to three questions:

    1)  

    What works well in the current US food safety system?

    2)  

    What changes would lead to a more effective food safety system?

    3)  

    What types of changes would be detrimental to an effective food safety system?

    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×

    A summary of the major points made by invited participants during the second workshop appears as Appendix D in the report.

    The final meeting of the committee, held June 12-14, 1998, did not include an open portion. At this meeting, the committee finished its major deliberations related to the report and finalized its recommendations.

    The Executive Summary presents the committee's principal findings and recommendations from its review of the four areas it was charged to consider. Chapter 1 provides an introduction to the issues and concerns related to food safety, including a brief history of food safety legislation since the early 1900's. Chapter 2 describes the current food safety system, with special attention to the federal role. Public health hazards resulting from the changing nature of pathogens and other toxicants are discussed in Chapter 3. Chapter 4 presents the committee's judgment regarding the attributes of a model food safety system. Chapter 5 compares the current federal system with the model system and identifies gaps. Chapter 6 includes the major conclusions and recommendations of the committee regarding changes needed in approaches and organizational structure to move toward a more effective food safety system. The appendices include reports and information related to the overall issues: Appendix A includes organizational charts, which identify the various components of the federal governments with functions related to food safety; Appendix B includes a recently released report from the Congressional Research Service outlining past recommendations for organizational change in food safety at the federal level; Appendix C includes the executive summary from Food Safety from Farm to Table: A National Food-Safety Initiative; Appendix D is a summary of points presented to the committee at their open meeting in April by representatives of various groups with interests in food safety, Appendix E includes information provided by federal agencies on levels of funding attributed to the major components of food safety for the years 1995-98, and Appendix F acknowledges the many individuals who assisted the committee by providing comments and materials in the information-gathering phase of the study.

    This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the NRC Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the IOM and the NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The content of the final report is the responsibility of the IOM, NRC, and the study committee, and not the responsibility of the reviewers. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. The Committee to Ensure Safe Food From Production to Consumption thanks the following individuals, who are neither officials nor employees of the IOM or the NRC, for their participation in the review of this report: Francis F. Busta, University of Minnesota; Lester Crawford, Georgetown University; Bernard D. Goldstein, UMDNJ-Robert Wood Johnson Medical School; Ray Hankes,

    Page viii Cite
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×

    Preferred Stock Genetic, Inc.; Carol Tucker Foreman, Foreman, Heiderpriem and Mager, Inc.; Cynthia M. Harris, Florida A&M University; Donald Hornig, Harvard University; Malden Nesheim, Cornell University; Stuart E. Richardson, California Department of Health Services; Mark Silbergeld, Consumers Union; and Bruce Stillings, Food & Agriculture Consultants. While the individuals listed above have provided many constructive comments and suggestions, it must be emphasized that responsibility for the final content of this report rests entirely with the authoring committee, the IOM, and the NRC.

    On behalf of the committee, it is a pleasure to thank Allison Yates, study director, senior staff officers Charlotte Kirk Baer and Sandra Schlicker, research associate Elisabeth Reese, IOM policy intern Kate Gorton, and project assistants Geraldine Kennedo and Melinda Simons. Their efforts were essential to the timely conclusion of our mission. Additionally, the committee thanks Michael Phillips for his assistance as director of the Board on Agriculture and Shirley Thatcher, his administrative assistant, and Norman Grossblatt of the Commission on Life Sciences for his valued editorial assistance early in the development of the report. We thank Michael A. Edington from the IOM Reports and Information Office for assistance in the production of the report and Claudia Carl, who managed the report review process. We also thank all who provided comments to the committee during the course of its deliberations.

    It is a pleasure also to record my personal thanks to the committee itself, which accomplished a prodigious amount of high-quality analysis and interpretation in a very short time.

    JOHN C. BAILAR III,

    CHAIR,

    COMMITTEE TO ENSURE SAFE FOOD FROM PRODUCTION TO CONSUMPTION

    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
       

    The Role of Media-Government Partnerships in Food Safety Education

     

    42

       

    Research and Development

     

    43

       

    Federal Research Activities

     

    43

       

    Application of New Technology

     

    45

       

    International Dimensions

     

    46

       

    Food Safety Efforts of Other Countries

     

    46

       

    US Regulation of Imported Foods

     

    47

       

    Summary Findings: The Current US System for Food Safety

     

    49

    3

     

    THE CHANGING NATURE OF FOOD HAZARDS: CAUSE FOR INCREASING CONCERN

     

    51

       

    Changes that Affect the Epidemiology of Foodborne Disease

     

    51

       

    Diet

     

    52

       

    Commercial Food Service

     

    54

       

    Methods of Production and Distribution

     

    54

       

    New or Re-emerging Infectious Foodborne Agents

     

    55

       

    Populations at High Risk for Severe or Fatal Foodborne Disease

     

    56

       

    Changes in Chemical Hazards Associated with the Food Supply

     

    57

       

    New Food Components

     

    58

       

    New Food Technologies

     

    59

       

    New or Re-emerging Toxic Agents

     

    59

       

    Physical Hazards

     

    60

       

    Summary Findings: The Changing Nature of Food Hazards

     

    61

    4

     

    WHAT CONSTITUTES AN EFFECTIVE FOOD SAFETY SYSTEM?

     

    63

       

    The Mission of the System

     

    63

       

    General Attributes of the System

     

    65

       

    The Importance of Partnering

     

    67

       

    The Roles of Government Partners

     

    67

       

    A Science-Based Foundation Using Risk Analysis

     

    68

       

    Adequate Surveillance and Monitoring

     

    69

       

    Focused Education and Research

     

    69

       

    Effective and Consistent Regulation and Enforcement

     

    71

       

    Response and Adaptation to New Technology and Changing Consumer Needs

     

    71

       

    Human and Financial Resources

     

    72

       

    The Roles of Private-Sector Partners

     

    73

       

    Producers

     

    73

       

    Processors, Marketers, and Distributors

     

    74

       

    The Role of the Consumer

     

    75

       

    The Role of Other Partners

     

    76

       

    A Dynamic Interdependence

     

    77

       

    Summary Findings: An Effective Food Safety System

     

    78

    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×

    5

     

    WHERE CURRENT US FOOD SAFETY ACTIVITIES FALL SHORT

     

    79

       

    Inadequate Application of Science

     

    80

       

    Research Funding Levels

     

    81

       

    Recent Efforts to Improve Research

     

    82

       

    Inadequate Use of Risk Assessment

     

    82

       

    Insufficient Information

     

    83

       

    HACCP Systems and Their Limitations

     

    84

       

    Absence of Focused Leadership

     

    85

       

    Statutory Limitations

     

    85

       

    Lack of Coordination

     

    87

       

    Deficiencies in Regulation of Imported Food

     

    89

       

    Summary Findings: Where the US Food Safety System Falls Short

     

    90

    6

     

    CONCLUSIONS AND RECOMMENDATIONS

     

    91

       

    Scientific Recommendations

     

    92

       

    Rationale for Recommendations Related to a Science-Based System

     

    95

       

    Role of Risk Analysis

     

    96

       

    Resources Required for Research

     

    96

       

    Recommendations to Implement a Science-Based System Through Organizational Changes

     

    97

       

    Rationale for Organizational Recommendations

     

    98

       

    Centralized and Unified Federal Framework

     

    98

       

    Integration of Food Safety Efforts

     

    99

     

     

    REFERENCES

     

    101

     

     

    APPENDIXES

     

    105

       

    AGlossary and Organizational Framework for Current Food Safety System

     

    105

       

    BCRS Report for Congress, Food Safety: Recommendations for Changes in the Organization of Federal Food Safety Responsibilities, 1949-1997

     

    115

       

    CExecutive Summary: Food Safety From Farm to Table: A National Food-Safety Initiative

     

    161

       

    DSummary of Comments and Testimony from Workshop (April 29-30, 1998) and Agenda

     

    169

       

    EFederal Food Safety Budget Information

     

    181

       

    FAcknowledgments

     

    185

       

    GCommittee Biographical Sketches

     

    189

    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    This page in the original is blank.
    Page xiii Cite
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×

    Ensuring Safe Food From Production to Consumption

    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    This page in the original is blank.
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R1
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R2
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R3
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R4
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R5
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R6
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R7
    Page viii Cite
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R8
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R9
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R10
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R11
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R12
    Page xiii Cite
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R13
    Suggested Citation:"Front Matter." Institute of Medicine. 1998. Ensuring Safe Food: From Production to Consumption. Washington, DC: The National Academies Press. doi: 10.17226/6163.
    ×
    Page R14
    Next: Executive Summary »
    Ensuring Safe Food: From Production to Consumption Get This Book
    ×
    Buy Paperback | $48.00 Buy Ebook | $38.99
    MyNAP members save 10% online.
    Login or Register to save!
    Download Free PDF

    How safe is our food supply? Each year the media report what appears to be growing concern related to illness caused by the food consumed by Americans. These food borne illnesses are caused by pathogenic microorganisms, pesticide residues, and food additives. Recent actions taken at the federal, state, and local levels in response to the increase in reported incidences of food borne illnesses point to the need to evaluate the food safety system in the United States. This book assesses the effectiveness of the current food safety system and provides recommendations on changes needed to ensure an effective science-based food safety system. Ensuring Safe Food discusses such important issues as:

    What are the primary hazards associated with the food supply? What gaps exist in the current system for ensuring a safe food supply? What effects do trends in food consumption have on food safety? What is the impact of food preparation and handling practices in the home, in food services, or in production operations on the risk of food borne illnesses? What organizational changes in responsibility or oversight could be made to increase the effectiveness of the food safety system in the United States?

    Current concerns associated with microbiological, chemical, and physical hazards in the food supply are discussed. The book also considers how changes in technology and food processing might introduce new risks. Recommendations are made on steps for developing a coordinated, unified system for food safety. The book also highlights areas that need additional study. Ensuring Safe Food will be important for policymakers, food trade professionals, food producers, food processors, food researchers, public health professionals, and consumers.

    1. ×

      Welcome to OpenBook!

      You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

      Do you want to take a quick tour of the OpenBook's features?

      No Thanks Take a Tour »
    2. ×

      Show this book's table of contents, where you can jump to any chapter by name.

      « Back Next »
    3. ×

      ...or use these buttons to go back to the previous chapter or skip to the next one.

      « Back Next »
    4. ×

      Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

      « Back Next »
    5. ×

      Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

      « Back Next »
    6. ×

      To search the entire text of this book, type in your search term here and press Enter.

      « Back Next »
    7. ×

      Share a link to this book page on your preferred social network or via email.

      « Back Next »
    8. ×

      View our suggested citation for this chapter.

      « Back Next »
    9. ×

      Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

      « Back Next »
    Stay Connected!