preface by

The RAND Graduate School dissertation series reproduces dissertations that have been approved by the student's dissertation committee. RAND is a nonprofit institution that helps improve policy and decisionmaking through research and analysis. RAND ® is a registered trademark. RAND's publications do not necessarily reflect the opinions or policies of its research sponsors. © Copyright 1999 RAND All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means (including photocopying, recording, or information storage and retrieval) without permission in writing from RAND. Published 1999 by RAN