title: [Behavioral characteristics of the only child vs first-born and children with siblings].
abstract: OBJECTIVE
  To assess the impact of being an only child on characteristics of parental and peer relationships, school achievement, social and sexual behavior.
  
  
  METHODS
  In the total, 360 adolescents identified at third year of high school were sampled from a private school from Porto Alegre in 2000 and 2001. Fifteen to nineteen years old male and female were selected in a cross-sectional study. Assessment of demographic data, education of the parents, birth order (only child, first born and non-first born children), cigarette smoking, alcoholic beverages consumption, illicit drug use, school achievement, social and sexual behavior were gathered with a pre-tested self-administered questionnaire, anonymously fulfilled at the classroom.
  
  
  RESULTS
  This study encompassed 8% of only children, 35% first-born, and 57% non-first born adolescents of a socioeconomic homogeneous sample. Social behavior, parents and peer relationships, sports participation, smoking and illicit drug were not associated with birth order. Only children were less likely to report an episode of alcohol intoxication (39%) than first-born (68.9%; p=0.03) and adolescents with siblings (72.3%; p<0.001). Only children had high school achievement than adolescents with siblings (p=0.03). Sexual behavior distinguished only children due to younger age at first sexual intercourse and lower rate of heterosexual self-identification, which persisted even after adjustment for confounding variables in comparison with non first-born adolescents (p=0.038).
  
  
  CONCLUSIONS
  Our findings suggest that the status of being only child is not associated with a poor outcome in several areas of the development. The impact of the presence of siblings in the development of sexual identification should be further explored.
authors.affiliation: Faculdade de Medicina, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Marcelo B
authors.initials: MB
authors.lastname: Tavares
authors.forename: Felipe Costa
authors.initials: FC
authors.lastname: Fuchs
authors.forename: Felipe
authors.initials: F
authors.lastname: Diligenti
authors.forename: José Ricardo Pinto
authors.initials: JR
authors.lastname: de Abreu
authors.forename: Luis Augusto
authors.initials: LA
authors.lastname: Rohde
authors.forename: Sandra Costa
authors.initials: SC
authors.lastname: Fuchs
mesh_terms: D000293:Adolescent; D000294:Adolescent Behavior / Q000523:psychology*; D000328:Adult; D000435:Alcoholic Intoxication / Q000523:psychology; D001722:Birth Order / Q000523:psychology*; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D008297:Male; D009863:Only Child / Q000523:psychology* / Q000706:statistics & numerical data; D010287:Parent-Child Relations; D012725:Sexual Behavior / Q000523:psychology; D035781:Siblings / Q000523:psychology*; D012919:Social Behavior; D012959:Socioeconomic Factors; D014477:Underachievement