title: Sample selection may bias the outcome of an adolescent mental health survey: results from a five-year follow-up of 4171 adolescents.
abstract: OBJECTIVE
  The representativeness of the data is one of the main issues in evaluating the significance of research findings. Dropping out is common in adolescent mental health research, and may distort the results. Nevertheless, very little is known about the types of systematic bias that may affect studies in a) the informed consent phase and b) later in follow-up phases.
  
  
  METHODS
  The authors addressed this gap in knowledge in a five-year follow-up study on a sample of adolescents aged 13-18 years.
  
  
  METHODS
  The data were collected using self-report questionnaires. The baseline sample consisted of 4171 adolescents, 1827 (43.8%) of whom gave consent to be contacted for a follow-up survey, but only 797 (19.1%) participated in the follow-up. Binary logistic regression models were used to explain the participation.
  
  
  RESULTS
  Young age, female gender, a high number of hobbies, good performance at school in the native language and general subjects, family disintegration such as divorce, high parental employment, and symptoms of depression and anxiety were associated with both consent and participation. However, the effect of mental health aspects was smaller than the effect of age and gender.
  
  
  CONCLUSIONS
  This study confirmed the possibility of systematic selection bias by adolescents' sociodemographic characteristics. The representativeness of the study sample might have been improved by more intense recruitment strategies.
authors: Department of Adolescent Psychiatry, Kuopio University Hospital, P.O. Box 100, FI-70029 Kuopio, Finland. Electronic address: virve.kekkonen@kuh.fi.
authors: V
authors: V
authors: Kekkonen
authors: School of Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland.
authors: P
authors: P
authors: Kivimäki
authors: Department of Health and Social Management, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland.
authors: H
authors: H
authors: Valtonen
authors: Department of Psychiatry, Päijät-Häme Central Hospital, Keskussairaalankatu 7, FI-15850 Lahti, Finland; School of Medicine, University of Tampere, FI-33014 University of Tampere, Finland.
authors: J
authors: J
authors: Hintikka
authors: Department of Adolescent Psychiatry, Kuopio University Hospital, P.O. Box 100, FI-70029 Kuopio, Finland; School of Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland.
authors: T
authors: T
authors: Tolmunen
authors: Department of Adolescent Psychiatry, Kuopio University Hospital, P.O. Box 100, FI-70029 Kuopio, Finland; School of Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland.
authors: S M
authors: SM
authors: Lehto
authors: Department of Adolescent Psychiatry, Kuopio University Hospital, P.O. Box 100, FI-70029 Kuopio, Finland; School of Medicine, University of Eastern Finland, P.O. Box 1627, FI-70211 Kuopio, Finland.
authors: E
authors: E
authors: Laukkanen
mesh_terms: D000293:Adolescent; D000367:Age Factors; D005260:Female; D005500:Follow-Up Studies; D006306:Health Surveys; D006801:Humans; D016015:Logistic Models; D008297:Male; D008603:Mental Health; D015983:Selection Bias; D057566:Self Report; D012737:Sex Factors
keywords: Attrition; Consent; Dropping out; Follow-up; Mental health; Responder