title: Longitudinal progression of negative symptoms in schizophrenia: a new look at an old problem.
abstract: OBJECTIVE
  Longitudinal analysis is crucial in determining the ability of new interventions to successfully reduce negative symptoms in schizophrenia. However, there are still conflicting reports as to whether there are significant treatment effects on these symptoms and the extent of these effects. We examine the possible effects of analysis method on these questions.
  
  
  METHODS
  We use generalized linear mixed models (GLMM) to assess the change in specific negative symptom items following treatment changes in two separate cohorts of schizophrenia patients, one chronic and one first episode.
  
  
  RESULTS
  Both data sets indicate that examining the change in prevalence of moderate to severe symptoms provides a useful estimate of the effect size associated with changes in treatment that often differs from that given using analysis of means.
  
  
  CONCLUSIONS
  The use of categorical longitudinal methods may be critical to determining the responsiveness of negative symptoms to treatment as well as determining the stability of these symptoms over time.
authors.affiliation: Department of Biostatistics, Rollins School of Public Health, Emory University, Atlanta, GA 30322, United States. mekelle@emory.edu
authors.forename: Mary E
authors.initials: ME
authors.lastname: Kelley
authors.forename: Gretchen L
authors.initials: GL
authors.lastname: Haas
authors.forename: Daniel P
authors.initials: DP
authors.lastname: van Kammen
mesh_terms: D000328:Adult; D017668:Age of Onset; D014150:Antipsychotic Agents / Q000627:therapeutic use; D002908:Chronic Disease; D003072:Cognition Disorders / Q000175:diagnosis* / Q000188:drug therapy* / Q000453:epidemiology; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D006220:Haloperidol / Q000627:therapeutic use; D006760:Hospitalization; D006801:Humans; D016014:Linear Models; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests / Q000706:statistics & numerical data; D015995:Prevalence; D011569:Psychiatric Status Rating Scales / Q000706:statistics & numerical data; D012559:Schizophrenia / Q000175:diagnosis* / Q000188:drug therapy* / Q000453:epidemiology; D012565:Schizophrenic Psychology; D012720:Severity of Illness Index; D016896:Treatment Outcome
chemical_list: D014150:Antipsychotic Agents; D006220:Haloperidol