title: Comparison between data obtained through real-time data capture by SMS and a retrospective telephone interview.
abstract: BACKGROUND
  The aims of the current study were: a) to quantitatively compare data obtained by Short Message Service (SMS) with data from a telephone interview, b) to investigate whether the respondents had found it acceptable to answer the weekly two SMS questions, c) to explore whether an additional weekly third SMS question would have been acceptable, and d) to calculate the total cost of using the SMS technology.
  
  
  METHODS
  SMS technology was used each week for 53 weeks to monitor 260 patients with low back pain (LBP) in a clinical study. Each week, these patients were asked the same two questions: "How many days in the past week have you had problems due to LBP?" and "How many days in the past week have you been off work due to LBP problems?" The last 31 patients were also contacted by telephone 53 weeks after recruitment and asked to recall the number of days with LBP problems and days off work for the a) past week, b) past month, and c) past year. The two sets of answers to the same questions for these patients were compared. Patients were also asked whether a third SMS question would have been acceptable. The test-retest reliability was compared for 1-week, 1-month, and 1-year. Bland-Altman limits of agreement were calculated. The two quantitative questions were reported as percentages. Actual costs for the SMS-Track-Questionnaire (SMS-T-Q) were compared with estimated costs for paper version surveys.
  
  
  RESULTS
  There was high agreement between telephone interview and SMS-T-Q responses for the 1-week and 1-month recall. In contrast, the 1-year recall showed very low agreement. A third SMS question would have been acceptable. The SMS system was considerably less costly than a paper-based survey, beyond a certain threshold number of questionnaires.
  
  
  CONCLUSIONS
  SMS-T-Q appears to be a cheaper and better method to collect reliable LBP data than paper-based surveys.
authors.affiliation: The Department of Research, the Spine Center, Hospital Lillebaelt, Oestre Hougvej 55, 5500 Middelfart, Denmark. bendtjohansen@gmail.com.
authors.forename: Bendt
authors.initials: B
authors.lastname: Johansen
authors.forename: Niels
authors.initials: N
authors.lastname: Wedderkopp