title: Positive and negative relationship between anxiety and depression of patients in pain: a bifactor model analysis.
abstract: BACKGROUND
  The relationship between anxiety and depression in pain patients has not been clarified comprehensively. Previous research has identified a common factor in anxiety and depression, which may explain why depression and anxiety are strongly correlated. However, the specific clinical features of anxiety and depression seem to pull in opposite directions.
  
  
  OBJECTIVE
  The purpose of this study is to develop a statistical model of depression and anxiety, based on data from pain patients using Hospital Anxiety and Depression Scale (HADS). This model should account for the positive correlation between depression and anxiety in terms of a general factor and also demonstrate a latent negative correlation between the specific factors underlying depression and anxiety.
  
  
  METHODS
  The anxiety and depression symptoms of pain patients were evaluated using the HADS and the severity of their pain was assessed with the visual analogue scale (VAS). We developed a hierarchical model of the data using an IRT method called bifactor analysis. In addition, we tested this hierarchical model with model fit comparisons with unidimensional, bidimensional, and tridimensional models. The correlations among anxiety, depression, and pain severity were compared, based on both the bidimensional model and our hierarchical model.
  
  
  RESULTS
  The bidimensional model analysis found that there was a large positive correlation between anxiety and depression (r = 0.638), and both scores were significantly positively correlated with pain severity. After extracting general factor of distress using bifactor analysis, the specific factors underlying anxiety and depression were weakly but significantly negatively correlated (r = -0.245) and only the general factor was significantly correlated with pain severity. Compared with the three first-order models, the bifactor hierarchical model had the best model fit.
  
  
  CONCLUSIONS
  Our results support the hypothesis that apart from distress, anxiety and depression are inversely correlated. This finding has not been convincingly demonstrated in previous research.
authors.affiliation: Department of Psychology, Fourth Military Medical University, Xi'an, People's Republic of China.
authors.forename: Jingdan
authors.initials: J
authors.lastname: Xie
authors.forename: Qian
authors.initials: Q
authors.lastname: Bi
authors.forename: Wen
authors.initials: W
authors.lastname: Li
authors.forename: Wen
authors.initials: W
authors.lastname: Shang
authors.forename: Ming
authors.initials: M
authors.lastname: Yan
authors.forename: Yebing
authors.initials: Y
authors.lastname: Yang
authors.forename: Danmin
authors.initials: D
authors.lastname: Miao
authors.forename: Huiming
authors.initials: H
authors.lastname: Zhang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001007:Anxiety / Q000503:physiopathology / Q000523:psychology*; D003863:Depression / Q000503:physiopathology / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008959:Models, Neurological; D010146:Pain / Q000503:physiopathology / Q000523:psychology*; D010147:Pain Measurement; D011594:Psychometrics; D012107:Research Design; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires