title: Citation bias and selective focus on positive findings in the literature on the serotonin transporter gene (5-HTTLPR), life stress and depression.
abstract: Caspi et al.'s 2003 report that 5-HTTLPR genotype moderates the influence of life stress on depression has been highly influential but remains contentious. We examined whether the evidence base for the 5-HTTLPR-stress interaction has been distorted by citation bias and a selective focus on positive findings.
  
  
  
  A total of 73 primary studies were coded for study outcomes and focus on positive findings in the abstract. Citation rates were compared between studies with positive and negative results, both within this network of primary studies and in Web of Science. In addition, the impact of focus on citation rates was examined.
  
  
  
  In all, 24 (33%) studies were coded as positive, but these received 48% of within-network and 68% of Web of Science citations. The 38 (52%) negative studies received 42 and 23% of citations, respectively, while the 11 (15%) unclear studies received 10 and 9%. Of the negative studies, the 16 studies without a positive focus (42%) received 47% of within-network citations and 32% of Web of Science citations, while the 13 (34%) studies with a positive focus received 39 and 51%, respectively, and the nine (24%) studies with a partially positive focus received 14 and 17%.
  
  
  
  Negative studies received fewer citations than positive studies. Furthermore, over half of the negative studies had a (partially) positive focus, and Web of Science citation rates were higher for these studies. Thus, discussion of the 5-HTTLPR-stress interaction is more positive than warranted. This study exemplifies how evidence-base-distorting mechanisms undermine the authenticity of research findings.
authors: Department of Psychiatry,Interdisciplinary Center Psychopathology and Emotion Regulation,University of Groningen,University Medical Center Groningen,Groningen,The Netherlands.
authors: Y A
authors: YA
authors: de Vries
authors: Department of Psychiatry,Interdisciplinary Center Psychopathology and Emotion Regulation,University of Groningen,University Medical Center Groningen,Groningen,The Netherlands.
authors: A M
authors: AM
authors: Roest
authors: Department of Psychology,University of Groningen,Groningen,The Netherlands.
authors: M
authors: M
authors: Franzen
authors: MRC Integrative Epidemiology Unit (IEU) at the University of Bristol,Bristol,UK.
authors: M R
authors: MR
authors: Munafò
authors: Department of Psychiatry,Interdisciplinary Center Psychopathology and Emotion Regulation,University of Groningen,University Medical Center Groningen,Groningen,The Netherlands.
authors: J A
authors: JA
authors: Bastiaansen
mesh_terms: D015706:Bibliometrics; D003865:Major Depressive Disorder / Q000209:etiology / Q000235:genetics; D006801:Humans; D017594:Publication Bias / Q000706:statistics & numerical data*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000502:physiology*; D013315:Stress, Psychological / Q000150:complications
chemical_list: C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins
keywords: 5-HTTLPR; Citation bias; depression; stress