Design: Feasibility study incorporating two phases in the MRC's framework for evaluating complex interventions. In Phase I a review of current resources that promote walking (and in particular the benefits of walking to work) will be undertaken: and focus groups (n=3) with employees and interviews with employers (n=3) will be conducted in three workplaces (small, medium, large) outside of Bristol to finalise the intervention design. Phase II will comprise an exploratory randomised trial in 12 workplaces (6 intervention, 6 control not involved with the Phase 1) in Bristol to examine recruitment and retention rates and variation in outcome measures, estimate possible effect sizes and explore other requirements of a full-scale trial. Whilst a cluster trial will in general require a larger sample size and more complicated analyses, randomising participants rather than workplaces may be subject to substantial contamination in which individuals randomised to the control group are exposed to some or all of the intervention being given to another group and hence may compromise the evaluation. An integral process evaluation will include post intervention interviews with employers, Walk to Work promoters, employees who become walkers and non-walkers to examine: the context, delivery and receipt of the intervention; and facilitators and barriers of walk to work initiatives from the perspectives of employers and employees. An assessment of intervention costs to participating employers and employees will also be undertaken.
Setting: The intervention will take place in Bristol. With a population of 433,100 people, Bristol is the largest city in the South West and one of the eight core cities in England, excluding London. The areas of highest population growth are all concentrated around the city centre and nearly half (46%) of all jobs are located in the city centre. A substantial number of people in Bristol travel short journeys to work by car. The Greater Bristol Cycling Strategy estimated that there are 45,000 people who use cars for journeys to work of less than 5km in length on a daily basis. The intervention will be implemented in six workplaces (2 small, 2 medium, 2 large) where a sizeable proportion of employees live within two miles of the workplace but do not currently walk to work (ascertained through a pre-intervention questionnaire). Six similar workplaces will comprise the control arm.
Target population: Employees who live within two miles of their workplace and are able to walk to work but do not usually walk or cycle to work.
Intervention: Information packs for the Walk to Work promoters (employees of participating companies in the intervention arm) will be developed by members of the research team following a resource review and focus groups during Phase 1. The packs will include the health, environmental, economic and social benefits of walking to work derived from, for example, Walk4Life, Walkit.com urban route planner, www.walkingworks.org.uk/ , www.walktoschool.org.uk/ . Specific behaviour change techniques that are likely to be used include: providing information on the link between walking and health; identifying barriers and ways to overcome them; prompting self-monitoring by use of a diary; identifying social support and relapse prevention. These techniques were used in the "Walk in to Work out" trial19 and have been recognised as having evidence for behaviour change.
There are four main stages of the intervention:
• Eligible employees (living within two miles of the workplace who are able to walk to work but do not currently walk or cycle to work) will be identified through workplace records (matching postcodes of workplace and home address, and checking for disability status or other disqualifying factors e.g. delivery drivers who usually set off from home in the workplace vehicle).
• Walk to Work promoters, nominated by participating employers, will be trained by expert members of the research team about the health, social, economic and environmental benefits of walking to work and how to identify and promote safe walking routes for employees. They will be given resource packs and trained to access relevant websites and toolkits [for example Walkit.com; Walkingworks.org.uk; Livingstreets.org]. The training will include communication strategies to give the Walk to Work promoters the confidence to encourage other employees to walk to work. The aim will be a maximum of 25 participants to each walk-to-work promoter. To manage the risk of absence of the Walk to Work promoter, one additional promoter will be recruited and trained in each workplace.
• All eligible employees will be invited to a work-based group session, organised and delivered by the Walk to Work Promoter, lasting about one hour at which the benefits of walking to work will be presented and discussed. Employees who express an interest in walking to work will 'sign up' at this stage. Safe, feasible walking routes will be identified. Goals for walking to work will be set.
• Further encouragement will be provided through four contacts from the Walk to Work promoter over the following 10 weeks (face-to-face, email or telephone as appropriate).
Intervention costs: Packs for the Walk to Work promoters will be compiled from existing resources (Dr Adrian Davis to lead - not charged to the study). Participating companies will bear the costs of the Walk to Work promoters' and employees' time spent on the intervention. The potential benefits of a healthier workforce and reduction in absentee rates will be stressed as a compensating factor. The full costs of the intervention will be assessed as part of the study.
Measurement of outcomes and duration of follow-up
Baseline: Eligible employees in intervention and control arms will be asked to complete a questionnaire giving basic personal data including postcode (to assess distance from home to work), job title, mode of transport to work, before and after work 'routines' affecting travel mode (for example, school run), typical commuting costs, household car ownership, commute related adverse events, health service use and views about walking. Eligible employees will wear an accelerometer for 7 days from waking in the morning until going to bed at night to provide an objective measurement of physical activity (including intensity and step counts), and a personal GPS receiver during the journey to and from work to confirm the duration of the journey, quantify its contribution to overall physical activity and describe walking routes. A £10 gift voucher will be given to all participants who return accelerometers and GPS receivers with data for at least 3 full working days.
Immediately post intervention:Questionnaires will be administered in intervention and control arms to explore: attitudes towards and experiences of walking to work including perceived barriers and facilitators, and emotional and physical well-being. (We will approach the iconnect project, who have already developed questionnaires, for suitable questions which we may be able to use for comparison purposes.) Additional questions about the acceptability of the intervention will be included for the intervention arm only.
One year follow-up: Questionnaires, accelerometers and GPS receivers will be administered in intervention and control arms (as per baseline protocol).
Process evaluation (Intervention arm): Group sessions will be observed during the intervention period. Immediately post-intervention, interviews will be conducted with a random sample of employees who have increased walking to work (n=18), and employees who have not (n=18). A senior manager and the Walk to Work promoter(s) in each workplace will also be interviewed.
Costs: The costs of the intervention to employers will be assessed by recording all time spent on training the promoters, implementing the intervention among employees and any materials or resources used. Absentee data will be monitored. Costs to participants will be assessed by recording journey time, household commuting costs and expenses (e.g. walking shoes). Self-reported measures of health service use will allow us to provide preliminary evidence on the savings/costs to the wider society.
Sample size: A sample size calculation for a full RCT, with estimation of potential clustering within workplaces and potential feasible differences in outcome, is one of the outcomes of this study. For this exploratory trial the choice of 12 workplaces will allow an equal number of workplaces to be allocated to each group within small, medium and large workplaces and provide some information on variability within and between centres at baseline and follow-up. Baranowksi recommends that exploratory trials have at least 400 or 500 participants to allow results that will be valuable to take effective interventions forward to full scale randomised controlled trials, whilst rejecting those that are unlikely to be effective [1]. For the current study, the initial screening and subsequent purposive sampling of workplaces will aim to ensure that a minimum number of employees meet the inclusion criteria in small, medium-sized or large workplaces to give a target for participating eligible employees of 500 (40 from 4 small, 160 from 4 medium, 300 from 4 large workplaces).
Planned analyses: Statistical analyses will be largely descriptive. The proportions of companies and employees who provide consent and complete the study will be calculated. The proportion of eligible employees within each workplace will also be calculated. Reasons for non-eligibility, refusing consent and withdrawing from the study will be fully documented.
Within the intervention group, differences between employees who do and do not walk to work will be explored, particularly in relation to socio-economic status, age and gender. Such exploration will be hypothesis generating but may be investigated further in a full trial if possible. In addition, any apparent differences may inform changes to the implementation or design of the 'Walk to Work' intervention prior to a full RCT.
Analyses of outcomes to be used as primary outcomes for a full trial (percentage walking to work, overall level and moderate+ physical activity) will be carried out at the employee level using multi-level regression models to account for the effects of clustering within workplaces. Models will adjust for baseline and covariates including age, gender and socio-economic status. As an exploratory trial the proposed study is not powered to provide a definitive comparison between the intervention and control groups and as such p-values will not be presented. However, estimates of effect and 95% confidence intervals will be generated. Confidence intervals will inform feasible effect sizes to be incorporated into sample size calculations for a full trial.
Whilst it may not be possible to obtain a reliable estimate of the intra-cluster correlation within the exploratory trial, 12 workplaces will provide some information about variability within and between workplaces and in addition to any estimates from previous literature will go some way to inform the sample size calculation for a full trial.
Accelerometer data will generate counts per minute at baseline and one year follow-up in intervention and control groups, and will also give data relating to bouts of moderate/vigorous physical activity. GPS data will be matched with accelerometer data to provide a measure of duration of the journey and associated physical activity.
Economic analyses will estimate the cost of the walk to work promoter training and intervention by multiplying the time spent by trainers and employees at the training day, work-based group session and booster sessions by the wage rate (including on-costs). Employees will be asked to provide details about their job title which will be used to estimate an indicative wage rate. All expenses (e.g. materials, equipment, room use) involved in the intervention will be documented. Full pay sick leave will be included as a cost to the employer (due to lost productivity). Unpaid sick leave will be included as a cost to the employee (due to lost income). Half pay sick leave will be included as a partial cost to both parties. We will measure and value any health service use due to commute-related adverse events during the year. We will also value self-reported general health service use in the past month at DC3 to provide preliminary information on any difference in health service costs. We will not assess cumulative health service costs throughout the year due to problems of recall. We will present results as a cost consequences study tabulating the costs and benefits of the intervention borne by employers, employees and others.
Qualitative analyses will employ constant comparison from grounded theory. Textual data will be scrutinised for differences and similarities within emerging themes, keeping in mind the context in which these arise. Qualitative analysis will be computer-assisted, using Nvivo software. The planned economic analysis is a cost consequence study tabulating the costs and savings to employees and employers alongside outcomes such as the % of eligible employees regularly walking to work and health service use.
Project timetables including recruitment rate
The study will take 27 months. Companies will be asked for expressions of interest at the beginning of the study including willingness to be randomised to the intervention and control arms, and permission for employees to participate in all study activities. The main stages of the study are:
Oct-Dec 2011. Ethics application; resource review; recruitment of companies; focus groups
Jan-Mar 2012. Data analysis; develop Walk to Work packs
Apr-Jun 2012. Baseline data collection; identify eligible employees; identify Walk to Work promoters; prepare individual packs
Jul-Sep 2011. Implement Walk to Work intervention; observations
Oct-Dec 2012. Post-intervention questionnaires and interviews
Jan-Mar 2013. Data analysis
Apr-Jun 2013. One year follow-up data collection
Jul-Dec 2013. Data analysis; paper writing; dissemination
The study is structured so that baseline and one-year follow-up fall within the same season.
1. Baranowski T, Cerin E, Baranowski J. Steps in the design, development and formative evaluation of obesity prevention-related behaviour change trials. International Journal of Behavioral Nutrition and Physical Activity 2009;6(1)6 [http://www.ijbnpa.org/content/6/1/6] |
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