title: Imputing missing standard deviations in meta-analyses can provide accurate results.
abstract: OBJECTIVE
  Many reports of randomized controlled trials (RCTs) fail to provide standard deviations (SDs) of their continuous outcome measures. Some meta-analysts substitute them by those reported in other studies, either from another meta-analysis or from other studies in the same meta-analysis. But the validity of such practices has never been empirically examined.
  
  
  METHODS
  We compared the actual standardized mean difference (SMD) of individual RCTs and the meta-analytically pooled SMD of all RCTs against those based on the above-mentioned two imputation methods in two meta-analyses of antidepressants.
  
  
  RESULTS
  Two meta-analyses included 39 RCTs of fluoxetine (n = 3,681) and 25 RCTs of amitriptyline (n = 1,832), which had actually reported means and SDs of the Hamilton Rating Scale for Depression. According to either of the two proposed imputation methods, the agreement between actual SMDs and imputed SMDs for individual RCTs was very good with ANOVA intraclass correlation coefficients between 0.61 and 0.97. The agreement between the actual pooled SMD and the imputed one was even better, with minimal differences in both their point estimates and 95% confidence intervals.
  
  
  CONCLUSIONS
  For a systematic review where some of the identified trials do not report SDs, it appears safe to borrow SDs from other studies.
authors.affiliation: Department of Psychiatry and Cognitive-Behavioral Medicine, Nagoya City University Graduate School of Medical Sciences, Mizuho-cho, Mizuho-ku, Nagoya 467-8601 Japan. furukawa@med.nagoya-cu.ac.jp
authors.forename: Toshi A
authors.initials: TA
authors.lastname: Furukawa
authors.forename: Corrado
authors.initials: C
authors.lastname: Barbui
authors.forename: Andrea
authors.initials: A
authors.lastname: Cipriani
authors.forename: Paolo
authors.initials: P
authors.lastname: Brambilla
authors.forename: Norio
authors.initials: N
authors.lastname: Watanabe
mesh_terms: D000639:Amitriptyline / Q000627:therapeutic use; D000928:Antidepressive Agents / Q000627:therapeutic use; D003627:Data Interpretation, Statistical; D003866:Depressive Disorder / Q000188:drug therapy; D005473:Fluoxetine / Q000627:therapeutic use; D006801:Humans; D015201:Meta-Analysis as Topic; D016032:Randomized Controlled Trials as Topic / Q000592:standards*
chemical_list: D000928:Antidepressive Agents; D005473:Fluoxetine; D000639:Amitriptyline