Original studies, study participants and ethics permission
Data were available from two randomized clinical trials (Study 1 and Study 2) carried out during 2007–9 as part of PhD projects. Results have been reported elsewhere for one of the studies [
7], but the other study has remained unpublished. The profile of the study participants and information on missing data, have been reported in detail elsewhere [
5].
Participants were aged 18–60 years and had been referred from general practitioners or chiropractors to a Danish outpatient spine clinic specializing in back pain. Those who fulfilled some minimal criteria (LBP or leg pain ≥3 out of 11 on a numerical rating scale, and a duration of 2–12 months), were screened with a baseline questionnaire and magnetic resonance imaging (MRI).
Patients originally invited to be included in Study 1 (N = 100) had localized LBP and any type of Modic changes that extended beyond the vertebral endplate, as defined by MRI. Treatment consisted of either a 10-week exercise program based on the “do not worry-keep active” concept or instructions to rest and refrain from hard work.
Participants in Study 2 (N = 258) were patients who were assumed to be suffering from non-specific LBP as they did not have an obvious acute disc problem or other pathology, and were not eligible for Study 1. The intervention group received a needs-based psychosocial approach in addition to the “usual” treatment provided to the control group that included physical examination, information, treatment in the form of training, spinal manipulation and/or medication as considered relevant by the treating clinician, and advice on continued management.
Baseline characteristics were similar for the intervention and control groups in each study. Thus in Study 1, the two groups were similar in terms of age, sex, body mass index, smoking, type of occupation, education, sick leave, LBP intensity, activity limitation, general health, and symptoms of depression. In Study 2, the two groups were similar in terms of age, sex, educational level, psychosocial profile, previous LBP and LBP intensity, dispute about work accidents, and activity limitation. Furthermore, outcomes and number of drop-outs were similar for the intervention and control groups in each study. For the purposes of the current study, therefore, the text message data have been combined for the intervention and control groups in each study, resulting in two samples for statistical analysis (one consisting of all participants in Study 1 and the other of all participants in Study 2).
Patients received written and verbal information about the study, signed informed consent forms and were allowed to withdraw from the study at any time without any consequences for their future treatment at the centre. Both studies were approved by the Ethics Committee for the Region of Southern Denmark (# S-VF-20060111 and 12165) and were registered in the ClinicalTrials.gov data base (Identification numbers NCT00454792 and NCT00459433). Permission for this additional analysis was given by the Research Department.
Data collection and storage
In the original studies, patients completed baseline and follow-up questionnaires and were also followed over 1 year with weekly automated text messages (SMS-Track.
http://www.sms-track.com). This report deals only with the SMS-Track data. Each week participants were asked, via a text message, how many days in the previous week they had experienced bothersome LBP. They answered by typing in the relevant number, e.g. 0 for no LBP, or three for 3 days of LBP. Their answers were automatically entered into a data file.
In Study 1, at the onset of the study, phone calls were made to people who failed to respond in order to provide extra explanation of how to respond to the text messages and to improve the compliance. This procedure was not used in Study 2.
Variable of interest and analysis of data
The current analysis used only one of the LBP variables that were collected. The item had the same wording in Study 1 and Study 2: “Using a number between 0 and 7, please answer how many days in the past week you have had problems with your lower back.”
Data were collected over 53 weeks. Out of the total number of weeks that a participant returned text messages, we calculated the percentage of weeks that the participants reported bothersome LBP for all seven days. We excluded participants who had none or only occasional responses during the study period. Some participants whose data sets were included in the analysis also had some missing data, but we decided against using imputation or worst/best case analysis. Instead, a separate analysis was made on study subjects who participated for less than 50 % of the weeks, to see if their profile was different from that of the others. No attempts were made to cluster findings on any other type of information.
The results are reported as percentages of weeks with 7 days of bothersome LBP and 95 % confidence intervals. Estimates were near-identical between the two studies, so it was not relevant to test for statistically significant differences.