Those who have sought information on the extent of divorce in the modern world will know that the most accessible sources lie in international yearbooks, (1) and that from these it is possible to make certain broad comparisons of a historical or geographical kind. For anyone country, for instance, changes in the divorce rate can be traced, or comparative rates for any number of countries at any given time can be examined. Similarly, it is possible to discover differences and similarities in divorce trends on an international basis, either for individual nations or for region­ al or cultural clusters. Typically, however, such sources cannot be used for detailed or sophisticated comparisons because of the limit­ ed volume of data, and of the nature of the statistics presented. To detect detailed differences in divorce-propensity by time or place, for instance, ideally requires cohort data, information on the number of marriages dissolved by divorce within one, two---x years among every 1,000 or 10,000 of marriages contracted in a given year. Such data do not appear in the international statistical summaries, which often do not even use the next best kind of measure, namely divorces per 1,000 or 10,000 existing marriages. Often the figures given are those for divorces per thousand of tot a I population, and these are of little comparative value because of variations in popu­ lation structure.

In 1971, the Dutch-language branch of the Population and Family Study Centre (CBGS)* of the Department of Public Health and the Family organized, in collaboration with investigators from the Rijksuniversiteit Gent, the Katholieke Universiteit Leuven, and the Vrije Universiteit Brussels, the Second National Fertility Survey in Belgium (NEGO 11)** (Cliquet et al. , 1970). NEGO II was a result of and related to the First National Fertility Survey performed in Belgium (NEGO I) in 1966 (Cliquet, 1967; Morsa, 1967). Both of these surveys were modelled on the Growth of American Families (GAF) studies performed at fiveyear intervals in the United States since 1955 (Freedman et al. , 1959; Whelpton et al. , 1966; Ryder and Westoff, 1971). Meanwhile, plans were made for the Third National Survey (NEGO III) in Belgium (CBGS Annual Report, 1975, 54). The CBGS fertility surveys (NEGO I-II-III) form part of the interdisciplinary research programme on the mating and reproductive behaviour of the Belgian population. In addition to these surveys, special investigations are performed in the Departments of Gynaecology and Obstetrics of various universities in Belgium. In the American surveys and similar studies done in many other countries, particularly those performed as part of the World Fertility Survey, the main emphasis has been given to the socio-demographic investigation of realized fertility and family planning. The approach applied by the CBGS has from the start placed these problems, both thematically and scientifically, in a wider perspective.

Since 1972 there has been a close contact through their publications between the Netherlands Interuniversity Demographic Institute at The Hague and the Population and Family Study Centre at Brussels. This co-operation has resulted in the joint publication of the journal Bevolking en Gezin (Population and Family) in the Dutch language. However, there has been a need for wider circulation of the Dutch language studies and research in the field of population and the family. In particular it was thought necessary to make possible an exchange of ideas and findings with popUlation and family scientists abroad. The volume Population and Family in the Low Countries intends to facilitate this international discussion by at least partially lifting the language barrier curtain. Some of the articles and documents included were originally published in the Dutch language, others were written especially for this volume. Population and family covers a very wide field and so do the chapters presented. In addition to demographic studies, articles are presented on population and family sociology and social biology. The editors hope that this second volume of Population and Family in the Low Countries reader, the sixth in their yearly publication series, will serve its purpose. The editors v Contents PREFACE V CONTRIBUTORS IX 1. J. GODEFROY A graphic representation of the process of population renewal - a demographic teaching aid . . . . . . . . . . . . . . . .

A few years aga the European Centre for Population Studies took the initiative in organizing a regular series of seminars which had the study of the demographie situation in Europe as goal. The First European Population Seminar took place in September of World Population Year 1974 in Karpacz, Poland and had as its topic "Urbanization and Population Growth in Europe" . A grant from the United Nations Fund for Population Aetivities made organizing this first seminar possible. In December 1976 the Seeond European Population Seminar was held in the Hague, The Netherlands. The ehoiee of topie for this seminar was a eombination of themes from the World Population Year 1974 and the International Women' s Year 1975. In both the World Population Plan as adopted at the World Population Conferenee in Bucharest and the World Plan of Action of the World Conferenee of the International Women's Year in Mexieo City, one finds the point of departure that a relation exists between demographie phenomena and the status of women. The subjeet of the seeond seminar was therefore formulated as: "Demographie Aspeets of the Changing Status of Women in Europe" .The Netherlands Demographie Soeiety, the Belgian Demographie Soeiety (Duteh-speaking seetionl and the European Centre for Population Studies ae ted as organizers, while two Duteh and one Belgian ministry provided subsidies. Finally, the institutional support of the Netherlands Interuniversity Demographie Soeiety and the Nether1ands Central Bureau of Statisties simplified organizing the seminar a great deal.

This book is an amended and somewhat shorter version of my doctoral thesis which I submitted to the Australian National University in 1976, and subsequently edited at the Netherlands Interuniversity Demographic Institute in 1977. The work falls naturally into two parts. The first is concerned with the construction and validation of a model, and the second with its application as an experimental tool. In the first part, comprising Chapters One to Four, an examination of historical and contemporary models of population growth led to the decision to study changes in fertility by means of a biological micro simulation model. The reasons supporting the choice of such a model were discussed, and a search of the literature produced the data to be used as model input. The effects of varying the input were examined and then the model output was tested against Hutterite data. The main emphasis of the second part of the work, comprising Chapters Five to Seven, was the testing of the effect on the fertility of one society of variations in the duration of the post partum period of non-susceptibility to conception, and in the level of infant and child mortality. Further simulations were performed to discover the impact on fertility of the use of contraception to attain different family sizes, both with and without the additional effect of infant and child mortality.

Since 1972 there has been a close contact through their pUblications between the Netherlands Interuniversity Demographic Institute at The Hague and the Population and Family Study Centre at Brussels. This co-operation has resulted in the joint pUblication of the journal BevoLking en Gezin (Population and Family) in the Dutch language. However, there has been a need for wider circulation of the Dutch language studies and research in the field of population and the family. In particular it was thought necessary to make possible an exchange of ideas and findings with population and family scientists abroad. The volume 'Population and family in the Low Countries' intends to facilitate this international discussion by at least partially lifting the language barrier curtain. Some of the articles and documents included were originally published in the Dutch language, others were written especially for this volume. Population and family covers a very wide field and so do the chapters presented. In addition to demographic studies, articles are presented on population and family sociology and social biology. The editors hope that this reader, the first in their yearly publication series, will serve its purpose.

1. BACKGROUND In the last ten years there has been much popular discus­ sion and also a great scholarly interest in the so-called "alternative lifestyles" (1). ESgecially, since the late 1J60's, a diversity of lifestyles other than the nuclear family began to emerge, according to demographic changes in household compositions during the past decade (US Bureau of Census, 1979; Centraal Bureau voor de Statistiek, 1930). One lifestyle, non-marital cohabitation, has increased most dra­ matically during the ~ast ten years and is the subject of this study. The term cohabitation will be used exclusively throughout the remainder of this study to refer to hetero­ sexual couples who are living together without being married legally. Despite its recent rapid increase, one should not overlook the fact that cohabitation, in comparison with legal marriage, remains an alternative practiced by a minority of the couples at any ?oint in time. For the Netherlands, it is estimated that 7 percent of all couples are living together unmarried, and 93 percent are married (Straver, 1981). This cohabitation rate is about twice as low when compared to rates in countries like Sweden and Denmark where they are 16 percent (the highest rate in Europe) and 13 percent (Trost, 1979), but still about twice as high when compared to the 3 percent estimate for the United States (Macklin, 1980).

Those who have sought information on the extent of divorce in the modern world will know that the most accessible sources lie in international yearbooks, (1) and that from these it is possible to make certain broad comparisons of a historical or geographical kind. For anyone country, for instance, changes in the divorce rate can be traced, or comparative rates for any number of countries at any given time can be examined. Similarly, it is possible to discover differences and similarities in divorce trends on an international basis, either for individual nations or for region­ al or cultural clusters. Typically, however, such sources cannot be used for detailed or sophisticated comparisons because of the limit­ ed volume of data, and of the nature of the statistics presented. To detect detailed differences in divorce-propensity by time or place, for instance, ideally requires cohort data, information on the number of marriages dissolved by divorce within one, two---x years among every 1,000 or 10,000 of marriages contracted in a given year. Such data do not appear in the international statistical summaries, which often do not even use the next best kind of measure, namely divorces per 1,000 or 10,000 existing marriages. Often the figures given are those for divorces per thousand of tot a I population, and these are of little comparative value because of variations in popu­ lation structure.

In 1971, the Dutch-language branch of the Population and Family Study Centre (CBGS)* of the Department of Public Health and the Family organized, in collaboration with investigators from the Rijksuniversiteit Gent, the Katholieke Universiteit Leuven, and the Vrije Universiteit Brussels, the Second National Fertility Survey in Belgium (NEGO 11)** (Cliquet et al. , 1970). NEGO II was a result of and related to the First National Fertility Survey performed in Belgium (NEGO I) in 1966 (Cliquet, 1967; Morsa, 1967). Both of these surveys were modelled on the Growth of American Families (GAF) studies performed at fiveyear intervals in the United States since 1955 (Freedman et al. , 1959; Whelpton et al. , 1966; Ryder and Westoff, 1971). Meanwhile, plans were made for the Third National Survey (NEGO III) in Belgium (CBGS Annual Report, 1975, 54). The CBGS fertility surveys (NEGO I-II-III) form part of the interdisciplinary research programme on the mating and reproductive behaviour of the Belgian population. In addition to these surveys, special investigations are performed in the Departments of Gynaecology and Obstetrics of various universities in Belgium. In the American surveys and similar studies done in many other countries, particularly those performed as part of the World Fertility Survey, the main emphasis has been given to the socio-demographic investigation of realized fertility and family planning. The approach applied by the CBGS has from the start placed these problems, both thematically and scientifically, in a wider perspective.

Since 1972 there has been a close contact through their publications between the Netherlands Interuniversity Demographic Institute at The Hague and the Population and Family Study Centre at Brussels. This co-operation has resulted in the joint publication of the journal Bevolking en Gezin (Population and Family) in the Dutch language. However, there has been a need for wider circulation of the Dutch language studies and research in the field of population and the family. In particular it was thought necessary to make possible an exchange of ideas and findings with popUlation and family scientists abroad. The volume Population and Family in the Low Countries intends to facilitate this international discussion by at least partially lifting the language barrier curtain. Some of the articles and documents included were originally published in the Dutch language, others were written especially for this volume. Population and family covers a very wide field and so do the chapters presented. In addition to demographic studies, articles are presented on population and family sociology and social biology. The editors hope that this second volume of Population and Family in the Low Countries reader, the sixth in their yearly publication series, will serve its purpose. The editors v Contents PREFACE V CONTRIBUTORS IX 1. J. GODEFROY A graphic representation of the process of population renewal - a demographic teaching aid . . . . . . . . . . . . . . . .

A few years aga the European Centre for Population Studies took the initiative in organizing a regular series of seminars which had the study of the demographie situation in Europe as goal. The First European Population Seminar took place in September of World Population Year 1974 in Karpacz, Poland and had as its topic "Urbanization and Population Growth in Europe" . A grant from the United Nations Fund for Population Aetivities made organizing this first seminar possible. In December 1976 the Seeond European Population Seminar was held in the Hague, The Netherlands. The ehoiee of topie for this seminar was a eombination of themes from the World Population Year 1974 and the International Women' s Year 1975. In both the World Population Plan as adopted at the World Population Conferenee in Bucharest and the World Plan of Action of the World Conferenee of the International Women's Year in Mexieo City, one finds the point of departure that a relation exists between demographie phenomena and the status of women. The subjeet of the seeond seminar was therefore formulated as: "Demographie Aspeets of the Changing Status of Women in Europe" .The Netherlands Demographie Soeiety, the Belgian Demographie Soeiety (Duteh-speaking seetionl and the European Centre for Population Studies ae ted as organizers, while two Duteh and one Belgian ministry provided subsidies. Finally, the institutional support of the Netherlands Interuniversity Demographie Soeiety and the Nether1ands Central Bureau of Statisties simplified organizing the seminar a great deal.

This book is an amended and somewhat shorter version of my doctoral thesis which I submitted to the Australian National University in 1976, and subsequently edited at the Netherlands Interuniversity Demographic Institute in 1977. The work falls naturally into two parts. The first is concerned with the construction and validation of a model, and the second with its application as an experimental tool. In the first part, comprising Chapters One to Four, an examination of historical and contemporary models of population growth led to the decision to study changes in fertility by means of a biological micro simulation model. The reasons supporting the choice of such a model were discussed, and a search of the literature produced the data to be used as model input. The effects of varying the input were examined and then the model output was tested against Hutterite data. The main emphasis of the second part of the work, comprising Chapters Five to Seven, was the testing of the effect on the fertility of one society of variations in the duration of the post partum period of non-susceptibility to conception, and in the level of infant and child mortality. Further simulations were performed to discover the impact on fertility of the use of contraception to attain different family sizes, both with and without the additional effect of infant and child mortality.

Since 1972 there has been a close contact through their pUblications between the Netherlands Interuniversity Demographic Institute at The Hague and the Population and Family Study Centre at Brussels. This co-operation has resulted in the joint pUblication of the journal BevoLking en Gezin (Population and Family) in the Dutch language. However, there has been a need for wider circulation of the Dutch language studies and research in the field of population and the family. In particular it was thought necessary to make possible an exchange of ideas and findings with population and family scientists abroad. The volume 'Population and family in the Low Countries' intends to facilitate this international discussion by at least partially lifting the language barrier curtain. Some of the articles and documents included were originally published in the Dutch language, others were written especially for this volume. Population and family covers a very wide field and so do the chapters presented. In addition to demographic studies, articles are presented on population and family sociology and social biology. The editors hope that this reader, the first in their yearly publication series, will serve its purpose.

1. BACKGROUND In the last ten years there has been much popular discus­ sion and also a great scholarly interest in the so-called "alternative lifestyles" (1). ESgecially, since the late 1J60's, a diversity of lifestyles other than the nuclear family began to emerge, according to demographic changes in household compositions during the past decade (US Bureau of Census, 1979; Centraal Bureau voor de Statistiek, 1930). One lifestyle, non-marital cohabitation, has increased most dra­ matically during the ~ast ten years and is the subject of this study. The term cohabitation will be used exclusively throughout the remainder of this study to refer to hetero­ sexual couples who are living together without being married legally. Despite its recent rapid increase, one should not overlook the fact that cohabitation, in comparison with legal marriage, remains an alternative practiced by a minority of the couples at any ?oint in time. For the Netherlands, it is estimated that 7 percent of all couples are living together unmarried, and 93 percent are married (Straver, 1981). This cohabitation rate is about twice as low when compared to rates in countries like Sweden and Denmark where they are 16 percent (the highest rate in Europe) and 13 percent (Trost, 1979), but still about twice as high when compared to the 3 percent estimate for the United States (Macklin, 1980).