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COMMITTEE ON POPULATION AND DEMOGRAPHY Report No. 22 Comparative Analysis of Fertility, Breastfeeding, and Contraception A Dynamic Mode! Toni Richards Panel on Fertility Determinants Committee on Population and Demography Commission on Behavioral and Social Sciences and Education National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1983

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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 This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The National Research Council was established by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal government. The Council operates in accordance with general policies determined by the Academy under the authority of its congressional charter of 1863, which establishes the Academy as a private, nonprofit, self-governing membership corporation. The Counci1 has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in the conduct of their services to the government, the public, and the scientific and engineering communities. It is administered jointly by both Academies and the Institute of Medicine. The National Academy of Engineering and the Institute of Medicine were established in 1964 and 1970, respectively, under the charter of the National Academy of Sciences. Available from National Academy Press 2101 Constitution Avenue, N.W Washington, D.C. 20418 Printed in the United States of America

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PANEL ON FERTILITY DETERMINANTS W. PARKER MAULDIN (Chair), The Rockefeller Foundation, New York ELBA BERQUO, Centro Brasileiro de Analise e Planej~mento, Sao Paulo, Braz il WILLIAM BRASS, Centre for Population Studies, London School of Bygiene and Tropical Medicine DAVID R. BRILLTNGER, Department of Statistics, University of California, Berkeley V.C. CHIDAMBARAK, World Fertility Survey, London JULIE DAV~NZO, Rand Corporation, Santa Monica RICHARD A. EASTERLIN, Department of Economics, University of Southern California, Los Angeles JAMES T. FAMCE:TT, East-West Population Institute, East-West Center, Honolulu RONALD FREEDMAN, Population Studies Center, University of Michigan DAVID GOLDBERG, Population Studies Center, University of Michigan RONALD GRAY, School of Hygiene and Public Health, The Johns Hopkins University, Baltimore PAULA E. HO7.r.ERBACH, Center for Policy Studies, The Population Council, New York RONAID rues, Graduate Group in Demography, University of California, Berkeley ROBERT A. LEVINE, Graduate School of Education, Harvard University S USAN C.M. SCRhMSMAW, School of Public Bealth, University of California, Los Angeles ROBERT WILLIS, Department of Economics, State University of New York, Stony Brook ROBERT J. LAPEAM, Study Director iii

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GOMMITT" ON POPt3LATION AM DEMOGRAPHY ANSLEY J. COALE (Chair), Off ice of Population Research, Princeton University WILLIAM BRASS,~Centre for Population Studies, London School of Hygiene and Tropical Medicine LEE-JAY COO, East-West Population Institute, East-West Center, Honolulu ROT FREEDMAN, Population Studies Center, University of Michigan NATHAN REMITS, Department of Sociology, Harvard University LESLIE RISE, Institute for Social Research, University of Michigan W. PARKER MAULDIN, Population Division, The Rockefeller Foundation, New York JANE ~EN, Office of Population Research, Princeton Univers ity SAMUEL PRESTON, Population Studies Center, University of Pennsylvania WILLIAM SELTZER, Statistical Of f ice, United Nations CONRAD TAEUBER, Kennedy Institute, Center for Population Research, Georgetown University ETIENNE VAN DE WALLE, Population Studies Center, University of Pennsylvania ROBERT J. LAPHAM, Study Director NOTE: Members of the Committee and its panels and working groups participated in this project in their individual capacities; the listing of their organizational aff iliation is for identif ication purpose s only, and the views and designations used in this report are not necessar fly those of the organizations mentioned . 1V

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CONTRAS L IST OF TABS LIST OF FIGURES LIST OF DIAGRAMS PREFACE: I NTRODUCTION DOTES ON THE DATA TEE: MODEL The Fertility Equation: Modeling the Time to Next Conception, 12 The Breastfeeding Equation: Modeling the Duration of Breastfeeding, 16 The Contraception Equation: Modeling Discontinuation Rstes, 18 m e Probability of Breastfeeding and the Probability of Using Contraception, 20 MOODS A Descr iptive Statistic for Duration Data: The Raplan-Meier Estimator of the Survivor Function, 22 A Continuous-Time Estimator of the Hazard Function with Time-Varying Covariates, 23 Sample Definition, 2S Definition of Variables Used in the Hazard Models, 25 Logistic Regression Analysis of the Probability of Bre~tfeeding and the Probability of Using Contraception, 30 v vii viii viii ix 1 4 9 22

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DESCRIPTIVE RESULT The Propensity to Breastfeed and ache Propensity to Contracept, 31 S urvivor Functions for Bir th Intervals, Duration of Breastfeeding, and Duration of Contraceptive Use, 32 Means and tr-~isnces of the Independent Variables Used in the Analysis, 33 FINAL RE;ULTS Logistic Regression Models for the Propensity to Breastfeed and for the Propensity to Contracept, 39 Hazard Adele for Termination of Breastfeedinq and Contraceptive Discontinuation, 40 Hazard Models for Conception, 57 SUIMARY OF RESULTS APPENDIX: RESUL" FOR PERIOD S==O~ RF~ER=CES 31 38 69 73 89 :4 vi

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LIST OF TABLES 1 Variable Definition for the Hazard Models 2 Cross-Tabulation of Breastfeeding and of Contraceptive Use for the Last Closed and the Open Interval 3 Means and Variances of Some Independent Variables Used in the Analysis 4 Logistic Regression for Probability of Breast- feeding and for Probability of Using Contraception in Last Closed or Open Birth Interval Coefficient Estimates for Termination of Breastfeeding: Colombia 6 Coefficient Estimates for Termination of Breastfeeding: Costa Rica 7 Estimates for Contraceptive Discontinuation: Colombia 8 Estimates for Contraceptive Discontinuation: Costa Rica Coefficient Estimates for the Fertility Equation: Colombia 10 Coefficient Estimates for the Fertility Equation: Costa Rica Al Logistic Regression for Probability of Breastfeeding, by Period A2 Logistic Regression for Probability of Using Contraception, by Period AS Coefficient Estimates for Termination of Breastfeeding, by Period: Colombia A4 Coefficient Estimates for Termination of Breastfeeding, by Period: Costa Rica AS Coefficient Estimates for Contraceptive Discontinuation, by Period: Colombia As Coefficient Estimates for Contraceptive Discontinuation, by Period: Costa Rica A7 Coefficient Estimates on the Fertility Equation, by Period: Colombia AS Coefficient Estimates on the Fertility Equation, by Period: Costa Rica . V11 28 32 37 40 43 44 48 52 60 64 74 75 76 77 80 82 84 86

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LIST OF FIGURES 1 Total Fertility Rates and Infant Hortality Rates, 1960-78 2 Age-specific Fertility Rates, 1960-75 3 Survivor Functions for Time to Next Live-Bir th Conception Survivor Functions for Duration of Breastfeeding Survivor Functions for Duration of Contraceptive Use 6 Hazard Functions for Termination of Breastfeeding and for Contraceptive Discontinuation 7 Hazard Functions with Covariates for Termination of Breastfeeding 8 Hazard Functions with Covariates for Contraceptive Discontinuation Hazard Functions for Live-Birth Conceptions Hazard Functions with Covariates for Live-Birth Conceptions LIST OF DIAGRAMS 1 Hazard Function for Conceptions for Women Who do not Breastfeed and do not Contracept 2 Hazard Function for Conception: Three Cases 3 A Two-Fold Mixed Weibull Density Function 4 Observed and Predicted Monthly Probabilities of Discontinuing Any Method Among Pill Acceptors . . V 111 6 34 3S 36 41 45 56 58 68 14 15 17 19

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PREFACE The Committee on Population and Demography was established in April 1977 by the National Research Council in response to a request by the Agency for International Development (AID) of the U.S. Department of State. It was widely felt by those concerned that the time was ripe for a detailed review of levels and trends of fertility and mortality in the developing world. Although most people in the demc- graphic community agree that mortality has declined in almost all developing countries during the last 30 years, there is uncertainty about more recent changes in mor- tality in some countries, about current levels of fertility, about the existence and extent of recent changes in fertility, and about the factors determining reductions in fertility. In 1963, a Panel on Population Problems of the Committee on Science and Public Policy of the National Academy of Sciences published a report entitled The Growth of World Population. The appointment of that panel and the publication of its report were expressions of the concern then felt by scientists, as well as by other informed persons in many countries, about the implications of population trends. At that time, He most consequential trend was the pronounced and long- continued acceleration in the rate of increase of the population of the world, and especially of the population of the poorer countries. It was estimated in 1963 that the annual rate of increase of the global population had reached 2 percent, a rate that, if continued, would cause the total to double every 35 years. The disproportionate contribution of low-income areas to that acceleration was caused by rapid declines in mortality combined with high ix

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f ertility that remained almost unchanged: the birth rate was nearly f iced or declined more Adeptly than the death rate. S ince the earlier report, however, the peak rate of growth in the world ' s population has apparently been passed. A dramatic decline in the birth rate in almost all the more developed counts ies has lowered their aggre- gate annual rate of increase to well below 1 percent, and the peak rate of increase has also apparently been passed in the les';-developed parts of the world as a whole. A sharp decline in fertility in many low~income areas has more than offset the generally continued reduction in the death rate, although the rate of population increase r emains high in almost all les~developed countries. The cause'; of the reductions in fertility--whether they are the effect primarily of such general changer as lowered infant mortality, increasing education, urban r ether than rural residence, and improving status of women, or of such particular changes as spreading knowl- edge of and acce';~; to efficient methods of contraception or abortion--are strongly debated. There are also diver gent views of the appropriate national and international policies on population in the face of these changing trends. The differences in opinion extend to different belief '; and aster tions about what the population trends really are in many of the less-developed countries. Because births and deaths are recorded very incompletely in much of Africa, Asia, and Latin America, levels and trends of fertility and mortality must be estimated, and disagreement has arisen in some instances about the most reliable estimates of those level`; Id trends. It was to examine these questions that the Committee on Population and Demography was established within the Commission on Behavioral and Social Sciences and Education of the National Research Council. It was funded for a period of five and one-half years by AID under Contract No. AID/pha-C-1161 and Grant No. AID/D6PE-G-0061. Chaired by Analey J. Coale, the committee has undertaken three mayor tasks: 1. To evaluate available evidence and prepare estimates of levels and trends of fertility and mortality in selected developing nations; 2. To ~ prove the technologies for estimating fertility and mortality when only incomplete or inadequate data exist (including techniques of data collection); 3. To evaluate the factors determining the changes in bir th rates in less-developed nations . - x

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Given the magnitude of these take, the committee decided to concentrate i" initial efforts on the first two take. milt work is detailed in a series of country and methodological reports frao the National Academy Press, and the deac~graphic estimation methodology developed for the country studies is laid out in a volume issued by the United Nations. As of 1982, some 170 population specialists, including 94 from developing countries, have been involved in the work of the committee as members of panels or work ing groups . me committee, the commission, and the National Research Council are grateful for the unpaid time and effort these experts have been willing to give. The committee initiated work on the third task in October 1979 when the separately funded Panel on Fertility Determinants was established. Research on the determinants of fertility change has been carried out by scholars from several disciplines, and there is no come prehensive accepted theory of fertility change to guide the evaluation. Because of this state of knowledge of the causes of reductions in fertility and the diffi- culty of the task, the Panel on Fertility Determinants includes scholars from anthropology, demcgra p y, economics, epidemiology, psychology, sociology, and statistics. Three committee members serve on the panel. m e work program of the panel includes the preparation of a report that attempts to summarize and integrate scientific knowledge about the determinants of fertility. In addition, the panel has prepared a few illustrative cross-national comparative analyses and studies of several developing countries. This report is one of the panel's comparative analysis studies. It has been prepared by Toni Richards, research associate, Office of Population Research, Princeton University, who was a National Academy of Sciences postdoctoral fellow with the committee in 1980-81. The initial work on this study was carried out at the Academy, and it was completed at the Office of Population Research (OPR) . The panel and the committee are grateful to th e author for preparation of the study and to the OPR for logistical support provided to the author. The author, panel, and committee would like to thank Henry Braun, Rodolfo Bulatao, Mark Montgomery, Rrishnan Namboodir i, Anne Pebley , T. Paul Schultz, Bur ton Singer James Trussell, and Bania Zlotnik for helpful comments xi

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and criticisms at various stages of the project. In addition, the report was reviewed by members of ~ panel and the committee. Charles Hammerslougb provided excellent programming assistance. Carol Ryner and Irene Martinez masterfully typed the text and many tables. Rona Briere edited the reports and Elaine McGarraugh assisted with the production details" W. PARKER MAuLpIN# Chair Panel on Fertility Determinants Ii