Fostervold 2006

Methods	The study is a randomised controlled trial with two interventions groups. A stratified randomisation procedure was used, where gender and age were regarded as potentially important prognostic factors and used as strata. The study was conducted in The National Insurance Services in Norway in 1999.
Participants	The participants were recruited from employees at The National Insurance Services in Oslo, Norway.  To be included in the study, the participants had to be between 18 and 62 years old and working between 70% and 100% of normal hours. Excluded were employees with known illness, planning to leave job or planning pregnancy. In total 150 employees out of 500 were selected. There were 75 participants in each group. All participants were experienced video display unit (VDU) users and used VDU above 50% of their working time. Thirteen workers left the study, giving a dropout rate of 9%.   Mean age was 41.1 years and 40.8 years in intervention group 1 and intervention group 2 respectively. Hundred and eleven female workers and 39 male workers participated in the study. Sex distribution was 55 females in intervention group 1 and 56 females in intervention group 2. MSD was assessed by a symptom questionnaire measuring 14 different symptoms. Prevalence of discomfort in neck and shoulder at baseline was 75% and 73.5% in intervention group 1 and 2 respectively.
Interventions	The intervention was installation of a new desktop with a submerged VDU screen into the table top. The computer screen was lowered and tilted backwards in two different angles. Intervention group 1 had a high line of sight (HLS) α = ‐15º, which means a line of sight 15º lower than a horizontal line.   Intervention group 2 had downward line of sight (DLS) α = ‐30º, which means a line of sight 30º lower than a horizontal line.
Outcomes	The following outcomes were measured at baseline and after 12 months: Subjective symptoms: A symptom questionnaire developed in‐house assessing 14 different symptoms was used. The symptoms were: Focusing difficulties, headache, discomfort in the neck and shoulder, discomfort in the back, discomfort in the arm, discomfort of the leg, skin symptoms, dizziness, nausea, concentration problems, general feeling of fatigue, discomfort in eyes, tired eyes, and reading problems. Each symptom was assessed by seven items. The first one categorical, determining whether or not the participant had experienced symptoms during the last three weeks. The remaining items were intensity and duration of that symptom. This was assessed on a seven‐step numeric scale with semantic descriptors at both ends and in the middle.  Health examination (included number of days absent due to illness during last six months): The examination comprised the following health indicators: Musculoskeletal tender or trigger points, neck mobility, presence of and intensity of any pain during neck movements, isometric/endurance test, palpation of tendon attachments, mobility in the shoulder joint and symptoms of carpal‐tunnel syndrome. In addition a structured clinical interview identified these issues: Known disease, prescribed medication, use of painkillers, received physiotherapeutic or chiropractic treatment, smoking, height, weight, number of days absent due to illness during last six months, and number of work days absent due to musculoskeletal problems in previous six months. Optometric status: This outcome was assessed by measuring refraction, contrast sensitivity, and the zone of clear single vision. Musculoskeletal load:  EMG (electrode electromyography) was used to measure muscle activity of neck and shoulder area. Control measures: Individual psychological states, satisfaction with the physical work environment and perceived work strain were measured to control for potential confounding factors. Control measurements of lighting, screen distance, and working hours in front of the VDU, were also recorded.
Notes	First author was contacted for missing information and responded.
Risk of bias
Bias	Authors' judgement	Support for judgement
Adequate sequence generation?	Low risk	According to first author it was used a between subjects design between units and a stratified design within each unit. Stratifying factors were gender and age. Block randomisation with a block size of four was used as randomisation procedure between units. A simple stratified lottery technique was used as assignment procedure. Drawing of lots is an adequate method of randomisation.
Allocation concealment?	Low risk	After recruitment each participant was allocated a case number comprising individual identification number and unit identification number. The people carrying out the assignment procedure did not conduct the number allocation. Neither were they part of the recruitment process. Information about the case number, age and gender were then handed over to the staff conducting the randomisation procedure. All this according to first author. This is an adequate method of allocation concealment.
Blinding? All outcomes ‐ participants?	High risk	It was impossible to blind the worker.
Blinding? All outcomes ‐ providers?	High risk	It was also impossible to blind the care provider to the intervention.
Blinding? All outcomes ‐ outcome assessors?	High risk	The study contained measures like self‐assessed questionnaire, optometric examination, health examination and musculoskeletal load. According to author, outcome assessors were blinded to the intervention except for measures of musculoskeletal load. Without all measurements blinded, it is not possible to score ´yes´.
Incomplete outcome data addressed? All outcomes ‐ drop‐outs?	Low risk	In total 9% of the participants dropped out of the study. They were evenly distributed between the groups. This is an acceptable drop‐out rate.
Incomplete outcome data addressed? All outcomes ‐ ITT analysis?	Low risk	Author has confirmed that all randomised participants were analysed in the group to which they were allocated.
Free of selective reporting?	Low risk	All outcomes are reported thoroughly. Based on an overall impression, ´yes´ is scored.
Similarity of baseline characteristics?	Low risk	Stratified randomisation was performed to ensure equally distribution of gender and age. Author provided information about sex distribution between the groups. The groups were similar at baseline regarding the important indicators; age and sex.
Co‐interventions avoided or similar?	Low risk	Co‐interventions were avoided according to author.
Compliance acceptable?	Low risk	Due to the nature of the interventions, the participants in both groups had to comply when doing computer work.
Timing outcome assessments similar?	Low risk	Author has confirmed that the timing of the outcomes assessments was similar in both groups.