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Michelle Campbell a Office of the President, Medical Research Council
of Canada, 1600 Scott Street, Ottawa, Ontario, Canada K1 OW9, b Division of Public Health and Primary Health Care, Institute
of Health Sciences, University of Oxford, Oxford OX3 7LF, c Department of Primary Care and Population Sciences,
Royal Free and University College Medical School, London NW3 2PF, d General Practice and Primary Care Research Unit, Department of
Public Health and Primary Care, Institute of Public Health, Cambridge
CB2 2SR, e Neuroscience Trials Unit, Department of
Clinical Neurosciences, Western General Hospitals NHS Trust, Edinburgh
EH4 2XU, f MRC Biostatistics
Unit, Institute of Public Health, Cambridge CB2 2SR, g Department of Public
Mental Health, Imperial College of Science, Technology, and Medicine,
St Mary's Campus, London W2 1PD
Correspondence to:
R Fitzpatrick raymond.fitzpatrick{at}nuffield.ox.ac.uk
Randomised controlled trials are widely accepted as the
most reliable method of determining effectiveness, but most trials have
evaluated the effects of a single intervention such as a drug.
Recognition is increasing that other, non-pharmacological interventions
should also be rigorously evaluated.1-3 This paper examines the design and execution of research required to address the
additional problems resulting from evaluation of complex
interventions
There are specific difficulties in defining, developing,
documenting, and reproducing complex interventions that are subject to
more variation than a drug. A typical example would be the design of a
trial to evaluate the benefits of specialist stroke units. Such a trial
would have to consider the expertise of various health professionals as
well as investigations, drugs, treatment guidelines, and arrangements
for discharge and follow up. Stroke units may also vary in terms of
organisation, management, and skill mix. The active components of the
stroke unit may be difficult to specify, making it difficult to
replicate the intervention. The box gives other examples of complex
interventions.
Service delivery and organisation: Interventions directed at health professionals' behaviour: Community interventions: Group interventions: Interventions directed at individual patients: Problems often arise in the evaluation of complex interventions
because researchers have not fully defined and developed the intervention. It is useful to consider the process of development and
evaluation of such interventions as having several distinct phases.
These can be compared with the sequential phases of drug development
(fig 1) or may be seen as more iterative (fig 2). Either way a phased
approach separates the different questions being asked.
Progression from one phase to another may not be linear. In many
cases an iterative process occurs The first step is to identify the evidence that the intervention
might have the desired effect. This may come from disciplines outside
the health sciences (such as theories of organisational change). Review
of the theoretical basis for an intervention may lead to changes in the
hypothesis and improved specification of potentially active
ingredients. In addition, previous studies may have provided some
empirical evidence Modelling or simulation techniques can improve understanding of
the components of an intervention and their interrelationships. Qualitative testing through focus groups, preliminary surveys, or case
studies can also help define relevant components. Descriptive studies
may help to delineate variants of a service. For example, hospital at
home schemes vary in purpose. Some are designed to hasten hospital
discharge, others to avoid hospital admissions, and yet others to
provide palliative care in the home.6
Qualitative research can also be used to show how the intervention
works and to find potential barriers to change in trials that seek to
alter patient or professional behaviour.7 For example, if
health professionals see the main barrier to changing their practice as
being lack of time or resources, an intervention that focuses only on
improving their knowledge will not work.
Acceptability and feasibility
that is, those "made up of various interconnecting
parts."4 The issues dealt with are discussed in a longer
Medical Research Council paper (www.mrc.ac.uk/complex_packages.html).
We focus on randomised trials but believe that this approach could be
adapted to other designs when they are more appropriate.
Summary points
Complex interventions are those that include several components
The evaluation of complex interventions is difficult because of
problems of developing, identifying, documenting, and reproducing the
intervention
A phased approach to the development and evaluation of complex
interventions is proposed to help researchers define clearly where they
are in the research process
Evaluation of complex interventions requires use of qualitative and
quantitative evidence
![]()
Challenges of trials of complex
interventions
Examples of complex interventions
Stroke units
Hospital at home
Strategies for implementing guidelines
Computerised decision
support
Community based programmes to
prevent heart disease
Community development approaches to
improve health
Group psychotherapies or behavioural
change strategies
School based interventions
for example, to
reduce smoking or teenage pregnancy
Cognitive
behavioural therapy for depression
Health promotion interventions
to reduce alcohol consumption or support dietary change
![]()
Framework for trials of complex interventions
for example, if an exploratory trial
finds that a complex intervention is unacceptable to potential recipients, the theoretical basis and components of the intervention may have to be re-examined. Preliminary work is often essential to
establish the probable active components of the intervention so that
they can be delivered effectively during the trial. Identifying which
stage of development has been reached in specifying the intervention
and outcome measures will give researchers and funding bodies
reasonable confidence that an appropriately designed and relevant study
is being proposed.
![]()
Preclinical or theoretical
phase
for example, an intervention may have been found
effective for a closely related condition or in another country with a
different organisation of health care.5

View larger version (31K):
[in a new window]
Fig 1.
Sequential phases of developing randomised
controlled trials of complex interventions

View larger version (16K):
[in a new window]
Fig 2.
Iterative view of development of randomised
controlled trials of complex interventions
![]()
Phase I: defining components of the intervention
![]()
Phase II: defining trial and intervention design
In phase II the information gathered in phase I is used to develop
the optimum intervention and study design. This often involves testing
the feasibility of delivering the intervention and acceptability to
providers and patients. Different versions of the intervention may need
to be tested or the intervention may have to be adapted to achieve
optimal effectiveness
for example, if the proposed intensity and
duration of the intervention are found to be unacceptable to participants.
Defining the control intervention
The content of the comparative arm (control group) of the main
trial will be decided during the preparatory phase. It may be an
alternative package of care, standard care, or placebo. Although
standard practice is often an appropriate control, it can be as complex
as the intervention being evaluated and may change with time. It is
thus important to monitor the care that is being delivered to the
control group. The use of a no treatment control group may be
unacceptable to patients. One possible solution is a randomised waiting
list study in which all participants ultimately receive the intervention.
Designing the main trial
The exploratory phase should ideally be randomised to allow
assessment of the size of the effect. This initial assessment will
provide a sound basis for calculating sample sizes for the main trial.
Other design variables can also be established in an exploratory trial.
Outcomes
Outcome measures for the main trial will also generally be piloted
during the exploratory phase. Investigators should include outcomes
that not only are relevant to patients with the disease or condition
being studied but also encompass measures of wider relevance to the
health system, including economic measures.8 Collection of
data to assess a full range of costs to patients, carers, and society
adds considerably to the workload and costs of researchers and may
challenge the feasibility of a trial. Strategic choice of outcomes is
therefore needed.9
for example,
prescribing particular treatments
is effective.
| |
Phase III: methodological issues for main trial |
|---|
The main trial will need to address the issues normally posed by randomised controlled trials, such as sample size, inclusion and exclusion criteria, and methods of randomisation, as well as the challenges of complex interventions. Individual randomisation may not always be feasible or appropriate. For example, cluster randomisation is often used for trials of interventions directed at a practice or hospital team. 10 11 Randomised incomplete block designs have also been used to evaluate different approaches to promoting change in professional behaviour.12
It is often not possible to conceal allocation of treatment from the patient, practitioner, and researcher in complex intervention trials. The potential biases of unblinded trials therefore have to be taken into account. Dissimilar levels of patient commitment between intervention and control groups may cause differential dropout, making interpretation of results difficult. When patients have strong preferences, a preference trial design may be used; patients without strong preferences are randomised as usual but those with strong preferences receive their preferred treatment.13 The results of such trials can, however, be difficult to interpret.
The findings of trials of complex interventions are more generalisable
if they are performed in the setting in which they are most likely to
be implemented. Eligibility criteria must not lead to the exclusion of
patients
for example, on the grounds of age
who constitute a
substantial portion of those to whom the intervention is likely to be
offered when implemented in the health system. Poor recruitment to a
trial can also raise doubts about generalisability.
Qualitative study of the processes of implementation of interventions
in study arms of the main trial can further show the validity of
findings.14
| |
Phase IV: promoting effective implementation |
|---|
The purpose of the final phase is to examine the implementation of
the intervention into practice, paying particular attention to the rate
of uptake, the stability of the intervention, any broadening of subject
groups, and the possible existence of adverse effects. As in the case
of drug trials, this might be carried out by long term surveillance,
although currently there is no established mechanism for funding such activities.
| |
Conclusions |
|---|
Trials of complex interventions are of increasing importance
because of the drive to provide the most cost effective health care.
Although these trials pose substantial challenges to investigators, the
use of an iterative phased approach that harnesses qualitative and
quantitative methods should lead to improved study design, execution,
and generalisability of results.
| |
Acknowledgments |
|---|
We thank the participants at a MRC workshop on complex interventions for their contribution. This article represents the views of the authors and does not represent the official view of the Medical Research Council.
| |
Footnotes |
|---|
Competing interests: None declared.
| |
References |
|---|
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(Accepted 31 May 2000)
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