National Academies Press: OpenBook

Beyond the Blueprint: Directions for Research on Head Start's Families (1996)

Chapter: 5 Head Start Families in a Changing Economic Landscape

« Previous: 4 Examining Community-Head Start Collaborations
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

5
Head Start Families in a Changing Economic Landscape

Head Start was launched during an era when maternal employment, even among the poor, was far less prevalent than it is today. Evidence regarding long-term welfare dependence had not yet become an issue, and there was greater public tolerance for nonemployment among mothers with young children eligible for Aid to Families with Dependent Children (AFDC). Contemporary rates of employment and pressures toward labor force participation for low-income mothers, including those with very young children, contrast sharply with this earlier portrait. Among children under age 5 in families with household incomes below $15,000, 29 percent are being raised by two employed parents or by a working single parent, typically the mother (Brayfield et al., 1993).

A large share of parents in Head Start families are also employed. More than one-third of Head Start children have at least one parent who works full time; another 15 percent have parents who work part time or seasonally, and 5 percent of children have parents who are in school or training (U.S. Department of Health and Human Services, 1993). In contrast, employed single-parent families are underrepresented in Head Start (Hofferth, 1994). Although Head Start programs currently have legislative authority to use funds for full-day services, administrative policies over the past several years have discouraged such practices (U.S. Department of Health and Human Services, 1993). Only 6.5 percent of Head Start

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

children were served for 8 hours a day in 1991-1992. However, in the context of welfare-to-work initiatives, the recently amended Head Start Act (1994) contains a provision that requires the Department of Health and Human Services to conduct a study of the extent to which Head Start programs are addressing the need for services during a full working day or full calendar year among eligible low-income families with preschool children.

A hallmark of Head Start has been its focus on addressing the developmental needs of young children and involving parents as partners in this process. Today, as the needs of parents increasingly involve full-time work and as mothers in poverty are mandated to work, meeting parents' needs takes on new meaning. Not surprisingly, in a 1990 survey conducted by the National Head Start Association, parents most often listed the need for extended hours and days of operation of Head Start centers as an area that needed improvement.

Janet Swartz informed the roundtable that more than 90 percent of the caseworkers in her research program mentioned employment when asked to identify the greatest needs of the families with whom they work and highlighted the importance of understanding the role of case management within Head Start.

Head Start also plays a significant role as a employer of Head Start parents. One-third of Head Start employees are former Head Start parents. And several Head Start programs are involved in extensive parent literacy and job training initiatives. These sets of issues surrounding Head Start's role in the economic dimension of poor families' lives—as employer, a site for job training, and a source of care for the children of working parents—surfaced repeatedly in the presentations and discussions among the roundtable members.

As welfare reform at the state level affects a growing share of Head Start-eligible families, pressures on the program to articulate its relation not only to parents' childrearing responsibilities, but also to their responsibilities (and requirements) to prepare for and sustain paid employment, will mount.

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

Randale Valenti noted that, since welfare reform is unmistakably on the table politically, the pressing question is: What are the challenges associated with integrating Head Start with various parents' employment scenarios?

ISSUES FOR RESEARCH

The vision of Head Start is to launch children on a trajectory of school success and social competence that will, among other goals, reduce welfare dependence in the next generation. Today, however, parents living in poverty have also become the focus of developmental programs aimed at redirecting the trajectories of their lives away from dependence and toward economic self-sufficiency. The lives of Head Start children, as a result, are set in motion along two paths simultaneously—their own developmental path and that of their parents—both of which are being heavily orchestrated by public policies. As a pivotal institution in these families' lives, what possibilities are available to Head Start to redefine what it means to be a two-generational program in this new policy context? How can research help to identify these possibilities?

In addressing these questions, members of the roundtable first acknowledged that research that focuses on the changing economic landscape of Head Start-eligible families will confront a central tension concerning the program's fundamental goals. Head Start was not designed primarily to meet the child care needs of full-time, full-year employed parents. The relatively high quality of Head Start programs, compared with full-day community-based child care centers (see Layzer et al., 1993), may actually depend on their circumscribed hours of operation and clear focus on the developmental needs of children (as distinct from the employment-related needs of their parents). Yet even the Advisory Committee on Head Start Quality and Expansion noted that "Head Start can no longer continue to be a half-day program for children in those families that need full-day, full-year services" (U.S. Department of Health and Human Services, 1993:47).

In light of the tensions that surround this topic and recent examinations of pertinent policies by the Board on Children, Youth, and Families (see its two 1995 reports, New Findings on Children, Families, and Economic Self-Sufficiency and Child Care for Low-Income Families), the roundtable members identified three issues that warrant the immediate scrutiny of

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

research: (1) Head Start's role as a training ground and job site for the parents of enrolled children; (2) the implications of the new economic pressures on Head Start families for parent involvement strategies; and (3) effective approaches to providing high-quality, cost-effective, full-day services for the Head Start population. This last effort is an important step toward complying with the 1994 Head Start Act's provision of studying the full-day need for Head Start services. Hence, the exploration of new program options, which offer the opportunity to bridge the gap that still separates the child care and Head Start traditions in this country, was an overriding theme of the roundtable's discussions.

Head Start as a Catalyst for Employment

Few dispute that provisions to support the care of young children while their parents prepare for employment must be a central component of any welfare-to-work initiative. Although the benefits that may be provided are often meager and short term—a far cry from the vision of Head Start—those who craft job training and employment policies for families in poverty know that connections must be made to child care policy. Ironically, those who create policies for the early care and education of children in poverty are only now beginning to recognize the value of making connections to training and employment policy.

The roundtable heard from several pioneers in this area, including those who are involved with Head Start's family service centers,1 the founders of Project Match (see Box 3), and researchers involved in the evaluation of the Comprehensive Child Development Centers. 2 In addition, the roundtable had the benefit of the work of the Advisory Committee on Head Start Quality and Expansion, which gave special focus to parent literacy training in the context of Head Start. Based on this input, several issues that could benefit from new research were identified.

The first concerns the intersection between welfare policy and Head

1  

The goal of the Head Start Family Service Center Demonstration Projects is to ameliorate the interrelated problems of illiteracy, substance abuse, and unemployment, which limit the capacity of many Head Start families to achieve self-sufficiency. This project is conducted in collaboration with local community programs.

2  

The Comprehensive Child Development Program (CCDP) is a demonstration program funded by ACYF in 1989 to provide comprehensive care to low-income families at 24 sites throughout the country. The program aims to improve the cognitive, socioemotional, and physical development of low-income children.

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

Start policy. As a starting point, it would be beneficial to obtain basic information on the number and characteristics of Head Start families who also receive income support from the Aid to Families with Dependent Children program. More generally, it would be useful to gain a better understanding of the sources of income (e.g., earned, AFDC, child support, Medicaid, and other contributions) that constitute the economic resources of Head Start families. Because the greatest pressures toward labor force participation (and extensive participation) are likely to fall on the AFDC population, Head Start programs that serve large numbers of these families will be among the first child-focused programs to feel the impact of state and federal welfare reform experiments.

Second, efforts within Head Start to stretch parent involvement to embrace literacy and job training initiatives have generated important new insights into what it takes to successfully promote economic self-sufficiency. For example, progress, like development in general, is seldom linear or entirely predictable. These families and those who work with them experience alternating periods of progress and setbacks. As a result, flexibility around the sequencing and timing of activities (e.g., work first, then school), in the context of clear expectations and rewards for moving along a clear sequence of steps (e.g., register for a Graduate Equivalency Degree program, show up on time for the classes, take the exam), appears to be key to helping families with young children make the transition to employment. Another insight concerned the fact that these families do not have networks into the job market; not only do they need preparation for jobs, but also specific assistance finding jobs. Even more important, but challenging, is the task of helping these families keep jobs. Finally, the parenting role appears to be a powerful incentive that drives work effort. Programs that build on this, for example, by rewarding being on time with the child's drop-off at Head Start and then shifting to rewards for work-related timeliness, or developing work skills by training a parent to be the newsletter editor for their Head Start center, appear to have greater odds of success.

Third, not only is Head Start a locus for job preparation, but it also has historically served as a source of employment for low-income parents. In this context, the roundtable members raised several questions for research: What are the career trajectories of the parents who are employed by Head Start both prior to and after working in the program? What are their earnings trajectories? What barriers presently militate against the successful translation of employment in Head Start to potentially more lucrative

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

employment in other settings? How does parent employment in Head Start affect their children's (those in and not in Head Start) motivation in school and aspirations for the future? Research that approaches these parents as workers and as models of employment for their children should be viewed as integral to the goals of Head Start.

Parent Involvement in the New Economic Context

Schooling, job training, and employment inevitably restrict the options for parent involvement that are realistically available to Head Start families. For all parents, the demands of the workplace are increasingly impinging on the time and energy that they can make available for their children. Parents who are raising children in the context of poverty are not immune from these pressures. Indeed, given the nonstandard work schedules and inflexibility that tend to characterize low-wage work (see Hofferth, 1994), they may feel these pressures even more acutely than other families. Models of parent involvement that were developed in an era when the majority of low-income mothers did not work require reexamination in this era when economic viability entails substantial work effort and expectations about poor families entail job preparation and employment regardless of the number and ages of children at home.

The roundtable members heard evidence gathered from interviews with Head Start families about their experiences, which highlighted the numerous barriers to parent involvement that currently exist. A prominent issue is the lack of adequate child care for the siblings of Head Start children and during non-Head Start hours, which is when parent meetings often occur. Mental health problems such as depression, health problems and disabilities, and work and school schedules were also frequently cited as barriers to parent involvement.

Susan Young suggested doing case studies of parents and their initial encounters with Head Start for the purpose of identifying life circumstances that support or discourage parent involvement.

In this context, the design and deployment of effective parent involvement strategies warrant careful examination. One set of issues pertains to the strategies that are available to staff for involving parents. These strategies presently encompass a range of rather different activities:

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
  1. Participation, mainly of parents, in the governance of the Head Start center in which their children are (or have been) involved;

  2. Participation of family members on a voluntary or paid basis as assistants or teachers working with children at Head Start centers;

  3. Participation of family members in community actions designed to improve conditions of life for poor families with young children;

  4. Creation of mutual support groups among Head Start families who can call upon assistance from each other as the need arises; and

  5. Provision to Head Start parents (and other adult family members) of information and training that can enable them to be more effective in caring for and interacting with their children.

Research is needed, nevertheless, to distinguish forms of parent involvement that are now most likely to enhance the development of young children growing up in poor families—increasingly with employed parents—and to identify a broader range of ways to involve parents, including those focused on literacy and job skills, than is currently the norm within Head Start. A central challenge involves identifying strategies that can be tailored, first, to the other demands that characterize parents' lives and, second, to their motivation and capacity to get involved. The importance of examining strategies that take into consideration the ways in which family members other than mothers (e.g., fathers, grandparents) participate in the lives of their children was of special interest to the roundtable members. For example, the roundtable members highlighted the importance of the role that grandparents and community elders play in childrearing, especially in multigenerational families. Grandparents are particularly important as primary caregivers with teenage parents. Research is needed to identify promising avenues for involving these individuals in Head Start.

James Levine argued that programs again and again have demonstrated that fathers can be involved in Head Start programs and that, when they are, there are benefits to the child and to the family. He urged the roundtable to rethink the problem of establishing parent involvement, to bring in the whole family.

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

Because new strategies will be only as effective as the staff who implement them, there is a critical need to reorient staff development and training to highlight strategies for working with irregularly involved parents, including exploration of the staffs' feelings about the parents they are trying to engage. Approaches that (1) encourage first steps, (2) offer meaningful forms of participation to parents with different capabilities and different circumstances, and (3) establish relationships of mutual respect with parents and staff warrant careful documentation and study.

Finally, and especially prominent in the roundtable's discussions about new strategies for parent involvement, were concerns about the social realities that even the most creative approaches to parent involvement now confront. What else is needed in order to ensure effective parent involvement? Child care is a clear and relatively straightforward need. Mental health and substance abuse services may be another element of effective parent involvement strategies at some, if not many, Head Start sites. Migrant Head Start programs have faced daunting challenges in offering opportunities for parent involvement and might be an especially useful source of ideas for overcoming some of the community-and family-based conditions that militate against effective, sustained parent involvement.

Full-Time Needs and Part-Day Programs

It is becoming increasingly evident that many Head Start programs are inaccessible to single employed parents who are nevertheless eligible to enroll their children. Head Start predominantly serves eligible children of nonworking parents and those who are in education and training programs prior to employment (Brayfield et al., 1993; Hofferth, 1994). This suggests that Head Start runs the risk of being beyond the reach of precisely those families in poverty who are struggling to do everything right as now defined by prevailing attitudes about dependence and work. Furthermore, the Head Start and child care communities have joined to share resources and construct effective bridges across their respective services in only a handful of exemplary sites. Keenly aware of these circumstances, the Advisory Committee on Head Start Quality and Expansion called on researchers to study efforts aimed at improving coordination and collaboration across Head Start and other early childhood programs in local communities.

To learn more about effective means of providing for child care that meets comparable quality standards as Head Start programs and provides

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

employment opportunities for family members, ACYF is conducting an evaluation of the Head Start-Family Child Care Demonstration project. The goal of this project is to provide Head Start services through family child care homes. Preliminary findings suggest that Head Start services equivalent to those of center-based programs can be provided in a family child care home.

Again, the roundtable members identified a cluster of research issues that bear on the challenges arising from pressures for extensive labor force participation by poor parents. How individual children are distributed across the various prekindergarten and child care programs that now exist in most localities remains largely a mystery. Given an illogical system, a significant policy issue exists regarding the equity with which comparably poor children have access to and receive care that meets the high standards of Head Start and that provides a comparable range of services. The factors that impinge on children's selection into Head Start, the number and characteristics of children who do not enter Head Start and the quality of care they receive in the absence of Head Start, represent epidemiological and descriptive data needs that the roundtable members viewed as crucial to fulfilling many of Head Start's current goals.

To the extent that Head Start is being encouraged to consider collaborative models, its accompanying research enterprise must also be collaborative. One somewhat obvious manifestation of a more collaborative research agenda would be the inclusion, where appropriate, of non-Head Start programs in samples for Head Start research initiatives. The roundtable members were highly cognizant of the great divide that now characterizes the research literatures on child care, education, mental health, pediatrics, Head Start, and other related disciplines and was supportive of efforts aimed at bridging the disciplinary divides.

Perhaps the most useful target for research aimed at promoting continuity of care for Head Start children as their parents move into full-time jobs is the identification of feasible and cost-effective strategies for providing high-quality, full-day, full-year early childhood services. Because many of the factors that have deterred this goal have been financial and logistical in nature, effective research in this area will necessarily involve a number of technical and economic considerations. What approaches to linking funding mechanisms across various subsidy programs have served to protect families from arbitrary discontinuities in care? What regulatory and other top-down policy constraints need to be overcome to enable existing programs to establish effective linkages? What costs and benefits

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

are associated with differing approaches to covering the full hours of parental employment, including those that derive from within Head Start and those that are based elsewhere? What have we learned from the growing share of Head Start programs that have used various strategies to provide full-day services? What have we learned from existing efforts to extend Head Start-type services to other child care programs in local communities? What other out-of-home settings have 4-year-olds enrolled in Head Start attended prior to Head Start? While children are in Head Start, are they also attending other forms of child care? How do the practices and quality of these other settings compare to the environment of Head Start classrooms? What are their differential effects on child development?

NEXT STEPS FOR RESEARCH

The roundtable members identified five important directions for research in this area; grouped in terms of the three types of research agendas presented in Table 1.

Descriptive Agenda

5-1. To obtain an accurate portrait of reliance on public assistance and of the income sources that are available to children in Head Start families (including those provided by noncustodial fathers and other family members), consider appending a supplemental interview focused on these issues to family surveys that are in the field or being planned. Ideally, these questions could be asked repeatedly (every 6 months) during a family's involvement with Head Start to capture the dynamics of family income and employment in this population. Consideration could also be given to obtaining comparable data on a sample of Head Start-eligible but nonenrolled families to determine whether there are systematic differences between the income sources of enrolled and nonenrolled families living in poverty.

5-2. To document the effects of Head Start on parents' employment opportunities and career and earnings trajectories, conduct a prospective, longitudinal study of parents in a random sample of Head Start centers—some of whom obtain jobs within Head Start and some of whom obtain work elsewhere or do not obtain employment—and follow them through their early career moves. With careful documentation of selection effects, such a study could document Head Start's long-standing role as a ''leg up'' for many low-income parents into the labor force. In addition to documenting the work and earnings pathways of families in poverty, it would be

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×

beneficial to assess effects on family resources, family stability, child care arrangements, and child outcomes.

Descriptive, Quality, and Outcome Agendas

5-3. To continue to advance Head Start's efforts to provide high-quality, effective literacy and job training to its participating families, develop a systematic program of demonstration and evaluation research on different approaches to this type of two-generation program. What are the most critical ingredients of successful programs, defined in terms of outcomes for parents and children? Do these critical elements differ based on the characteristics of the families being served? Are the elements that promote the successful completion of training programs the same as those that enable parents to sustain employment?

5-4. To obtain a current profile of the range and intensity of parent involvement strategies currently being used in Head Start, and to provide a base for subsequent research on the effectiveness of different approaches with various families, support a descriptive study of current parent involvement practices in Head Start that relies on multiple informants and multiple methods of data collection (surveys, interviews, participant observations). Ideally, such a study would be designed to capture a "year in the life of" the family-Head Start interface, starting with recruitment and enrollment and continuing through several months after graduation from Head Start. Including programs that have experience with involving fathers, grandparents, and foster parents would be extremely worthwhile given the changing family demographics of Head Start children and the critical need to reassess current assumptions about whom to involve in Head Start.

5-5. To identify cost-effective approaches to providing for the full-time, full-year care needs of a growing share of Head Start families, conduct an economic analysis of differing strategies for providing full-day, full-year services. Among the models that are most pertinent to Head Start are those that compare the costs of differing approaches to full-day Head Start, such as wraparound programs, to the costs of supplementing the quality and comprehensiveness of existing, community-based child care programs—both family-based and center-based. To provide the most useful data regarding the comparative pros and cons of differing approaches, such a study would need to document both costs and benefits, including those that accrue over time (e.g., identification of health and developmental delays that can compromise early school achievement, parents' successful transition from welfare to employment, reduced behavioral problems in school).

Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 40
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 41
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 42
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 43
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 44
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 45
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 46
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 47
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 48
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 49
Suggested Citation:"5 Head Start Families in a Changing Economic Landscape." Institute of Medicine and National Research Council. 1996. Beyond the Blueprint: Directions for Research on Head Start's Families. Washington, DC: The National Academies Press. doi: 10.17226/5196.
×
Page 50
Next: 6 Extending the Benefits of Local Innovation »
Beyond the Blueprint: Directions for Research on Head Start's Families Get This Book
×
 Beyond the Blueprint: Directions for Research on Head Start's Families
Buy Paperback | $30.00 Buy Ebook | $23.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

On its 30th anniversary, public acceptance of Head Start is high, yet understanding of its goals is low, and evaluation research is limited in quality and scope. In this book, a roundtable of representatives from government, universities, medicine, and family support agencies identifies a set of research possibilities to generate a broader understanding of the effects of Head Start on families and children. Among the important issues discussed are the ethnic and linguistic diversity of Head Start families, the social conditions of the community context, and the implications of the changing economic landscape for both families and Head Start itself.

READ FREE ONLINE

  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!