Physical Activity Clinical Trial
Official title:
A Mixed-methods Evaluation of Sit-stand Workstations in an Office Setting: a Randomised Controlled Trial
The purpose of this study is to investigate whether a device that allows office workers to sit or stand whilst working can reduce their sitting time at work and improve their health over 8 weeks.
Study design
Treatment arms in this two-arm parallel-group randomised controlled trial (RCT) included a
sit-stand workstation intervention group (each participant received a sit-stand workstation)
and a control group (usual practice).
Recruitment
- Organisation level
Office workers from one organisation were targeted by the research team in August-September
2013. Consent was sought from 11 departmental managers for employee recruitment,
installation of sit-stand workstations, study contact and laboratory visits during work
time. Departments were located across four buildings with varying office layout (open-plan,
individual offices or a combination). Employees within the targeted departments were
predominantly administrative staff.
- Individual level
Via an email from the research team, all employees in consenting departments received an
overview of the study and participant information sheet, and were invited to a study
information session (two sessions were organised per department). Employees were given 2
weeks to express interest. Interested employees were screened for eligibility using stated
criteria by the research team via telephone. If inclusion criteria were met, written
informed consent was obtained and baseline assessments scheduled. There was no racial or
gender bias in the selection of participants.
Group assignment and Intervention
Following baseline assessments, participants were assigned by one member of the research
team to a treatment arm using a randomised block design and random number table. Departments
served as blocks and participants within departments were randomly assigned at the
individual-level to an arm. Assignment of individual participants within each department
alternated between arms (i.e. intervention, control, intervention, control…).
Data collection
At baseline, 4 weeks (mid-intervention) and 8 weeks (end-intervention), participants'
office-based behaviours were assessed via ecological momentary assessment (EMA) diaries. At
baseline and 8 weeks, participants attended University laboratories in the morning for
individual assessments of other stated outcomes. Prior to laboratory visits, participants
were required to fast for a minimum of 8 hours, avoid the consumption of alcohol for 12
hours, and avoid strenuous exercise for 24 hours.
Sample size
Allowing for small drop out, the study aimed to recruit 25 participants per arm, and retain
23 participants per arm. A sample size of 23 per arm was chosen a priori to achieve 90%
power (alpha 5%; two-tailed) to detect a minimum difference of 60 minutes/8-hour workday
between arms for workplace sitting time (primary outcome: expected SD of 60 minutes/day).
Data collection for vascular and metabolic outcomes would provide effect size estimates for
power calculations in subsequent trials.
Statistical analyses
- Data was analysed using the Statistical Package for the Social Sciences (SPSS) version
22 (IBM, New York, USA) with the alpha level set at p≤0.05. Intervention effects were
compared at 4 weeks (sitting, standing and walking) and 8 weeks (all outcomes) from
baseline using analysis of covariance (ANCOVA). The variable change score (4 or 8 weeks
minus baseline) was the dependent variable, with intervention arm (control vs
intervention) the independent variable. In all analyses, covariates were the baseline
value for the variable to control for any imbalances at baseline. Anthropometric,
sociodemographic, work-related and office-environment characteristics were tested as
potential confounders for all outcomes. Confounders were entered as covariates if
significant associations (p≤0.05) were observed with changes in an outcome and the
effect on the mean difference between groups exceeded 20%. For changes in sitting,
standing and walking time, baseline values of the other two behaviours were tested as
potential confounders, though no effects on the mean difference between groups exceeded
20%. Adjusted change scores and 95% confidence intervals (CIs) for the difference in
change between groups are presented unless stated otherwise. Acceptability and
feasibility data are reported as medians and quartiles.
- Missing data and Intention-to-treat analysis Due to participant withdrawal, lost EMA
diaries or the inability to conduct assessments, data were missing for all outcomes.
Accordingly, a per-protocol analysis was conducted and participants were excluded from
analyses for outcomes they were missing data for. For workplace sitting, standing and
walking, the per-protocol analysis was compared with an intention-to-treat analysis, as
a sensitivity analysis. To treat missing data, the fully conditional imputation
technique and ten imputation sets were used due to a low rate of missing data.
Imputation was based on all 47 randomized participants.
- Minimum important differences analysis Inferential statistics were ran using minimum
clinically important difference principles, described elsewhere. Briefly, this approach
makes inferences based on meaningful magnitudes and is recommended alongside hypothesis
testing. A spreadsheet computed the quantitative and qualitative probability that the
true effects were beneficial, trivial or harmful, after the outcome statistic, its p
value, and the smallest/minimal important difference was entered. Minimum important
differences for sitting and standing were 60 minutes/day, and for walking 10
minutes/day. Minimum important differences for other outcomes were determined through a
distribution-based method as a Cohen's d (standardized difference between change scores
between groups) of 0.2 between-subjects standard deviations (SDs). The SD of pooled
baseline data was used to negate the possibility of individual differences from the
intervention influencing the SD at 8 weeks. For each effect at 8 weeks, quantitative
probabilities for benefit, trivial and harm, and qualitative descriptors are reported.
Effects were interpreted as unclear if probabilities for benefit and harm were >5%.
;
Allocation: Randomized, Endpoint Classification: Efficacy Study, Intervention Model: Parallel Assignment, Masking: Open Label, Primary Purpose: Basic Science
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