Economic evaluation
The economic evaluation will estimate the incremental
cost and incremental benefit of the WAVES study intervention
compared to usual current practice, from a
NHS/educational service perspective. Additional wider
perspectives, such as inclusion of family members, will
be explored as part of a sensitivity analysis. A within-trial
analysis will estimate the cost-effectiveness at 18 months
assuming that the intervention is in a ‘steady state’ and
thus will not include set up or implementation costs. A
longer term analysis will estimate the cost effectiveness
using a decision-analytic model.
The within-trial analysis will adopt a micro-costing
approach to estimate the costs of each intervention component.
Trial report forms and school logbooks will
collect resource use information for staff time, materials,
transport, and equipment, combined with unit cost data
to estimate the incremental intervention mean cost per
class, and per child. Sensitivity analysis will explore intervention
fidelity, and the inclusion/exclusion of categories
of cost e.g. family members, set up, implementation.
Quality of life will be measured using the Child-Health
Utility 9D instrument and expressed as QALYs. Costeffectiveness
will be measured using both the effectiveness
outcomes (BMI z-score, proportion overweight/obese)
and QALY outcomes.
The long-term cost effectiveness analysis will use a
decision-analytic model to predict the cost-savings and
outcomes from preventing overweight/obesity in childhood.
Model parameters will be informed by a literature review
and will map outcomes from childhood to adulthood. Extensive
sensitivity analysis will be carried out, to test for
the robustness of the conclusions to assumptions made
in the modelling, and to sampling variation in the data
used in the construction of the model. Costs and benefits
will be discounted at the standard rate (3.5%).
Trial status
The trial started recruitment of schools in January 2011,
and of pupils from March 2011. Intervention delivery was
completed in July 2013. Final follow-up measurements
will be completed in April 2015. Data analysis will commence
following data cleaning (after June 2015). The expected
report date is November 2015.
Discussion
To our knowledge, the WAVES study is the first trial of
a childhood obesity prevention intervention that: has
been developed using the MRC framework for complex
interventions, tests both the clinical and cost-effectiveness
of a school-based intervention and will have sufficient
length of follow-up to examine longer term effects. The
trial setting includes a diverse socioeconomic and multiethnic
population to allow exploration of sub-group effects.
There is also consideration of a wide range of
outcomes, including psychosocial effects to monitor
potential harm.
The trial will address some of the limitations identified
in previous research [9], particularly including a sample
size large enough to detect clinically significant differences
in adiposity, use of an objective measure of physical activity,
inclusion of cost effectiveness evaluation, a comprehensive
process evaluation and assessment of longer term
outcomes (all schools at 18 months and half the schools at
27 months post intervention completion).
Given the pragmatic and complex nature of the trial, it
will not be possible to assess intervention efficacy directly
or to disentangle the relative contribution of different
intervention components to any observed outcomes. On the other hand, assessment of effectiveness in real settings
facilitates future intervention roll-out and dissemination,
should the intervention prove to be clinically
cost-effective. Thus, the study has the potential to influence
health and education policy in the UK and further
afield.
The comprehensive process evaluation and detailed assessment
of implementation alongside the trial will allow
us to contextualise and explain the findings of the trial
and inform future implementation. It will also allow us
to perform analyses to explore the relationship between
intervention implementation and outcomes, which has
not been undertaken in previous childhood obesity prevention
trials.
In addition to the findings of the trial, the study will
also provide a large dataset on the weight status and other
health indicators of a sub sample of multi-ethnic children
in the West Midlands, which can be used to address other
relevant research questions.