title: Handling missing items in the Hospital Anxiety and Depression Scale (HADS): a simulation study.
abstract: BACKGROUND
  The Hospital Anxiety and Depression Scale (HADS) is a widely used questionnaire in health research, but there is little guidance on how to handle missing items. We aimed to investigate approaches to handling item non-response, varying sample size, proportion of subjects with missing items, proportion of missing items per subject, and the missingness mechanism.
  
  
  METHODS
  We performed a simulation study based on anxiety and depression data among cancer survivors and patients. Item level data were deleted according to random, demographic, and subscale dependent missingness mechanisms. Seven methods for handling missing items were assessed for bias and imprecision. Imputation, imputation conditional on the number of non-missing items, and complete case approaches were used. One thousand datasets were simulated for each parameter combination.
  
  
  RESULTS
  All methods were most sensitive when missingness was dependent on the subscale (i.e., higher values of depression leads to higher levels of missingness). The worst performing approach was to analyze only individuals with complete data. The best performing imputation methods depended on whether inference was targeted at the individual or at the population.
  
  
  CONCLUSIONS
  We recommend the 'half rule' using individual subscale means when using the HADS scores at the individual level (e.g. screening). For population inference, we recommend relaxing the requirement that at least half the items be answered to minimize missing scores.
authors: Department of Epidemiology and Biostatistics, Mel and Enid Zuckerman College of Public Health, University of Arizona, 1295N. Martin Ave., P.O. Box 245163, Tucson, AZ, 85724, USA. melaniebell@email.arizona.edu.|Psycho-Oncology Co-Operative Research Group, School of Psychology, The University of Sydney, Level 6-North, The Lifehouse, 119-143 Missenden Rd, Sydney, NSW, 2006, Australia. melaniebell@email.arizona.edu.
authors: Melanie L
authors: http://orcid.org/0000-0003-4821-4094
authors: ML
authors: Bell
authors: Department of Biostatistics and Informatics, Colorado School of Public Health, 13001 E. 17th Place, Campus Box B119, Aurora, CO, 80045, USA.
authors: Diane L
authors: DL
authors: Fairclough
authors: Department of Epidemiology and Biostatistics, Mel and Enid Zuckerman College of Public Health, University of Arizona, 1295N. Martin Ave., P.O. Box 245163, Tucson, AZ, 85724, USA.
authors: Mallorie H
authors: MH
authors: Fiero
authors: Psycho-Oncology Co-Operative Research Group, School of Psychology, The University of Sydney, Level 6-North, The Lifehouse, 119-143 Missenden Rd, Sydney, NSW, 2006, Australia.
authors: Phyllis N
authors: PN
authors: Butow
mesh_terms: D001007:Anxiety; D003863:Depression; D006801:Humans; D011569:Psychiatric Status Rating Scales; D011795:Surveys and Questionnaires
keywords: Anxiety; Depression; Distress; Imputation; Missing data; Questionnaires; Simulation