There is a widespread belief that birth order is an important determinant of personality, intelligence, and economic success. This belief is supported by a number of recently published popular books, each with its own approach to the topic. Leman (2001, 16-18), for instance, argues that firstborns "are more highly motivated to achieve than later borns" and as a consequence "often fill positions of high authority or achievement." In contrast, Wallace (1999, 18), worries that firstborns "go through life feeling like they cannot measure up to the high standards their parents expected ... lacking in confidence they might drop out and refuse to compete altogether." (1)
Although there is an intuitive appeal to some of these theories, the weight of evidence suggests that birth-order effects of this nature either do not exist or are difficult to measure using the standard approaches of social scientists. A large number of empirical studies have examined the effect of birth order on test scores, education, and earnings--see Olneck and Bills (1979), Blake (1981), Hauser and Sewell (1983), Behrman and Taubman (1986), Kessler (1991), and Hanushek (1992). Taken together their results suggest that, after properly controlling for family size, birth order explains little variation in these conventional measures of success.
Another, more recent strand of research in this area examines whether the sex composition of an individual's siblings affects academic achievement as measured by years of education. In a well-known article, Butcher and Case (1994) present evidence that females raised with brothers go on to receive more education, on average, than that of females raised with at least one sister. However, even this relatively modest, albeit unexpected finding has been called into question by subsequent studies; note Kaestner (1997) and Hauser and Kuo (1998).
Using data on adolescents aged 12 through 17, we investigate the relationship between birth order and a number of behaviors that have been, for the most part, ignored in this literature. These behaviors include the probability that an individual smoked cigarettes, used substances such as marijuana or alcohol, engaged in sexual activity, or committed any one of a series of crimes. In contrast to what most empirical studies have found, we find strong evidence that birth order is related to many of the outcomes under study. We also show that at least one birth-order difference can last into early adulthood, if not beyond. Although it is difficult to isolate the precise routes through which birth order affects the behavior of adolescents, our results are consistent with the idea that peer influences play an important role.
II. WHY BIRTH-ORDER EFFECTS MIGHT EXIST
Researchers working in this area have long speculated that birth order might be related to child outcomes through parental investments in their offspring. Becker and Tomes (1976) posit a model in which parents devote more financial resources to children with lower innate ability. (2) If, as suggested by Behrman and Taubman (1986) and Kessler (1991), genetic endowments favor earlier-born children, this model would predict offsetting financial investments in later-borns. Under the assumption of "imperfect capital markets," Birdsall (1991) predicts greater expenditures on later-born children as family income rises and older siblings become financially independent, but the author also notes that firstborns do not initially have to compete for their parents' time and attention. In a frequently cited piece in the psychology literature, Zajonc (1976) likewise emphasizes the early period in a firstborn's cognitive development when parental attention is undivided. (3) In fact, most researchers working on birth-order issues have assumed that children are particularly sensitive to parental time investments and the home environment at young ages. (4) However, certain nonmonetary parental inputs, such as monitoring and supervision, may become increasingly important as a child matures, especially in the determination of risky or delinquent behaviors. …