title: Absence of low back pain in the general population followed fortnightly over one year with automated text messages.
abstract: BACKGROUND
  Over one year, the majority of patients with low back pain (LBP) from the secondary care sector could not report a single week without LBP and few could report a non-episode, defined as at least one month without LBP. Presumably, non-episodes would be more common in the general population. The aim of this study was to assess the usefulness of this definition of ´"non-episodes", by studying their presence over one year in the general population. Specifically, we wanted to: 1) determine the prevalence of non-episodes, 2) identify the proportion of study participants who could be classified as being in a non-episode at the end of the observation period, and 3) estimate the proportion of participants classified as having at least two separate non-episodes.
  
  
  METHODS
  Danes, aged 49/50, who previously participated in a population-based study on LBP received fortnightly automated text (SMS) messages over one year. Each time, participants reported the number of days with LBP in the preceding fortnight. Fortnights with 0 days of LBP were defined as 'zero-fortnights' and two such fortnights in a row (one month) were defined as a 'non-episode'. Estimates are reported as percentages with their 95% confidence intervals in brackets.
  
  
  RESULTS
  Two hundred and ninety-three people were invited to participate. Of these, 16 declined participation and 16 were excluded because they failed to return their text message at least 20 of the 26 times, leaving 261 in the current analyses. Of these, 11% (2-22) never reported a zero-fortnight. In all, 83% (78-88) had at least one non-episode throughout the study period and the proportion of participants classified as being in a non-episode at the end of the study was 59% (53-65). The percentage of individuals with at least two non-episodes was 52% (46-58).
  
  
  CONCLUSIONS
  It is possible to differentiate people from the general population as having or not having episodes of LBP using the definition of absence of LBP over one month as the measure. Non-episodes were far more common in the general population than in the secondary care sector, suggesting it to be a potentially useful definition in research.
authors.affiliation: Research Department, The Spine Center of Southern Denmark, Hospital Lillebælt and Institute of Regional Health Research, University of Southern Denmark, Østre Hougvej 55, DK5500 Middelfart, Denmark. clyde@health.sdu.dk.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Leboeuf-Yde
authors.forename: Nadège
authors.initials: N
authors.lastname: Lemeunier
authors.forename: Niels
authors.initials: N
authors.lastname: Wedderkopp
authors.forename: Per
authors.initials: P
authors.lastname: Kjaer