Peer Effects on a Fertility Decision: An Application for Medellín, Colombia
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Peer Effects on a Fertility Decision:
An Application for Medellín, Colombia

The world’s total fertility rate has fallen substantially in the last fifty years. The Latin American and Caribbean region is not an exception to this rule, as a deep process of demographic transition has swept through the entire region. In the first decade of this century, the region’s total fertility rate (TFR) fell from 2.67 children per woman in 1999 to 2.12 by the end of 2010. The current rate is surprisingly close to the widely accepted replacement rate of 2.1.

The evolution of the fertility rate for young populations is especially important because of the negative consequences of teenage childbearing, which is widely associated with low human development and poverty.1 In the last decade, the Latin American and Caribbean region also saw a reduction in the fertility rate for women between fifteen and nineteen years of age (FR15-19), from 83.95 children per 1,000 women in 1999 to 71.68 in 2010. While this reduction in the FR15-19 is substantial, it is smaller than the reduction in the TFR in the same period. Between 1999 and 2010, the TFR dropped 26 percent, while the FR15-19 fell 17 percent. This implies that adolescent fertility has become a more important component of total fertility in most of the countries in the region.2 Relative to adult fertility, adolescent fertility is becoming greater and greater in Latin America. [End Page 119]

With some exceptions like Argentina and Peru, the contribution of adolescent fertility to total fertility has increased continuously in almost all Latin American and Caribbean countries. In 1999, adolescent fertility was 15.72 percent of total fertility in developing Latin American and Caribbean countries; by 2010, this ratio had increased to 16.29 percent. There are some remarkable cases, such as Brazil and Ecuador, where the ratio of adolescent fertility to total fertility increased by more than two percentage points between 1999 and 2010. The result of this phenomenon is, on average, an earlier individual onset of childbearing.

To explain this interesting phenomenon, it is important to study the factors that determine the age at which a mother decides to have her first child. From an individual’s point of view, it may seem rational to have a child early in life given her education, her household socioeconomic conditions, and the characteristics of her social group. This paper explores the mother’s chosen timing for the onset of childbearing in an urban context in Colombia, emphasizing the role of peer effects and using longitudinal individual information that allows characterizing mothers before or at the time of the pregnancy.

Many social researchers in the last three decades have been interested in the phenomenon that takes place when an individual’s behavior is partly explained by the influence of other individuals’ behavior. In economics this has been called social interactions or peer effects. There are several channels through which these effects may take place: for example, individuals may learn from peers’ behavior (social learning), or they may embrace the norms of the community with regard to socially accepted practices (social influence).3 The main purpose of this paper is to test the existence and measure the magnitude of peer effects on a fertility decision. The fertility decision considered is the woman’s age at the onset of childbearing. The study draws on a large sample of poor mothers in the city of Medellín, who had their first child between 2001 and 2010.

Social interactions could be a potential explanatory factor in the reduction of the average age of mothers at first birth observed in Latin America and the Caribbean, and they could certainly be a cause for the high incidence of teenage pregnancy in countries such as Colombia. There is evidence on the existence of geographic sorting patterns governing the spatial distribution of several fertility outcomes in Latin American cities.4 For instance, in poor [End Page 120] neighborhoods women have more children and the onset of childbearing is earlier than in other neighborhoods. Nevertheless, the literature on fertility in the region has not explored the...