title: Differences in mail and telephone responses to self-rated health: use of multiple imputation in correcting for response bias.
abstract: OBJECTIVE
  To estimate differences in self-rated health by mode of administration and to assess the value of multiple imputation to make self-rated health comparable for telephone and mail.
  
  
  METHODS
  In 1996, Survey 1 of the Australian Longitudinal Study on Women's Health was answered by mail. In 1998, 706 and 11,595 mid-age women answered Survey 2 by telephone and mail respectively. Self-rated health was measured by the physical and mental health scores of the SF-36. Mean change in SF-36 scores between Surveys 1 and 2 were compared for telephone and mail respondents to Survey 2, before and after adjustment for sociodemographic and health characteristics. Missing values and SF-36 scores for telephone respondents at Survey 2 were imputed from SF-36 mail responses and telephone and mail responses to sociodemographic and health questions.
  
  
  RESULTS
  At Survey 2, self-rated health improved for telephone respondents but not mail respondents. After adjustment, mean changes in physical health and mental health scores remained higher (0.4 and 1.6 respectively) for telephone respondents compared with mail respondents (-1.2 and 0.1 respectively). Multiple imputation yielded adjusted changes in SF-36 scores that were similar for telephone and mail respondents.
  
  
  CONCLUSIONS
  The effect of mode of administration on the change in mental health is important given that a difference of two points in SF-36 scores is accepted as clinically meaningful. Health evaluators should be aware of and adjust for the effects of mode of administration on self-rated health. Multiple imputation is one method that may be used to adjust SF-36 scores for mode of administration bias.
authors.affiliation: Research Centre for Gender and Health, University of Newcastle, Callaghan, New South Wales. jenny.powers@newcastle.edu.au
authors.forename: J R
authors.initials: JR
authors.lastname: Powers
authors.forename: G
authors.initials: G
authors.lastname: Mishra
authors.forename: A F
authors.initials: AF
authors.lastname: Young
mesh_terms: D001294:Attitude to Health; D001315:Australia / Q000453:epidemiology; D015982:Bias; D003625:Data Collection / Q000379:methods* / Q000592:standards; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008875:Middle Aged; D011177:Postal Service; D012044:Regression Analysis; D012107:Research Design / Q000592:standards; D012647:Self-Assessment; D013689:Telephone; D016387:Women's Health