Academic journal article Demographic Research

Two Period Measures for Comparing the Fertility of Marriage and Cohabitation

Academic journal article Demographic Research

Two Period Measures for Comparing the Fertility of Marriage and Cohabitation

Article excerpt

(ProQuest: ... denotes formulae omitted.)

1. Introduction

Over the last decades, unmarried cohabitation has become a common mode of union formation in many Western countries and is becoming an established method of family formation in some of them. Consequently, childbearing within cohabitation is believed to have become common in a number of countries, and one could suspect that births within cohabitation account for a significant portion of overall fertility in countries were cohabitation is widespread. However, despite cohabitation becoming more common, there is not yet an easy and recognised way of assessing the respective contributions of marriage and cohabitation to fertility.

In this article, we introduce two measures that allow us to estimate the respective contributions of marriage and cohabitation to overall period fertility. These measures are based on a decomposition of the total fertility rate, in which the TFR is expressed as the sum of a series of contributions from conjugal status (i.e. living alone, cohabiting, or being married), and these contributions are expressed as the sum of weighted age-specific fertility rates, conditional on conjugal status. Unlike the marital (legitimate) or non-marital (illegitimate) ASFRs and TFR, whose values are typically larger than observed ASFRs and completed fertility, these measures take values that are "realistic" by design.

We begin by reviewing the current approaches to the comparison of fertility within marriage and cohabitation, and detailing the difficulties involved in this comparison. Next, we present the measures we are introducing. We continue with an example developed using Canadian census data.

2. Measuring the fertility of marriage and cohabitation

2.1 Previous research

Fertility is commonly estimated using vital statistics. Vital statistics commonly report whether children are born to married parents or an unmarried mother, but do not commonly report whether the unmarried mother is cohabiting with the child's father. Vital statistics are still largely computed following the traditional distinction between marital and nonmarital fertility - historically, legitimate and illegitimate fertility -, not acknowledging the social phenomenon of unmarried cohabitation. For this reason, fertility estimates for cohabitation based on vital statistics are a rarity; when available, they are limited to the number or proportion of children born to cohabiting women (Klüsener, Perelli-Harris, and Sánchez Gassen 2013). There is no established way to compare the fertility of marriage and cohabitation. A review of attempts performed since the 1990s shows that the proposed solutions are many, and gives insight into the difficulties of such a comparison.

Verdugo Lazo (1994) used an approach developed by Rodriguez and Cleland (1988) and survey data to estimate the fertility of four forms of union (civil and religious, civil only, religious only, and consensual) in Brazil. The technique relies on exposure time measured from the beginning of the union, and requires that women do not change the form of their union after its onset.

Dumas, Bélanger, and Smith (1998) compared the fertility of marriage and cohabitation in Canada using data from a retrospective biographical survey. They estimated five-year age group birth rates for each of the two forms of union, for two ten-year periods, 1975-1984 and 1985-1994, and for two regions: Quebec, and Canada without Quebec. They computed the total fertility rate (TFR) for each region and period, based on the conjugal status of the mother at the time of the birth of the child. They concluded that the fertility of cohabitation was lower than that of marriage in both regions and in both periods, but that the difference between the fertility level of marriage and cohabitation was smaller in Quebec than in the rest of Canada. These authors, despite using data from a biographical survey, based their comparison on the TFR, using the conjugal status at the time of birth to compute the denominators of the age-specific rates (ASFRs). …

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