opportunities for evaluation using the stepped wedge trial design celia brown, alan girling, prakash...
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Opportunities for evaluation using the Stepped Wedge trial design
Celia Brown, Alan Girling, Prakash Patil and Richard Lilford
Department of Public Health and Epidemiology
Today’s presentation Describe the stepped wedge design Detail when the design might be
useful Consider the advantages and
disadvantages of the design Review 12 studies employing a
stepped wedge design
The Stepped Wedge Design
One individual/cluster receives the intervention in each time period
Order of intervention determined at random
All individuals/clusters get the intervention by the end of the process
Data collected in each time period
5
4
3
2
11 2 3 4 5 6
Shaded cells represent intervention periodsBlank cells represent control periodsEach cell represents a data collection point
Time periods
Pa
rtic
ipa
nts
/Clu
ste
rs
When is the design useful? Prior belief that the intervention will do
more good than harm – ethics of exclusion
Logistical, practical or financial constraints to simultaneous intervention
Evaluating a public policy intervention that is being rolled-out before effectiveness demonstrated (e.g. Sure Start)
Advantages Enables RCT approach in situations
where parallel design not possible Can model the effect of time of
intervention on effectiveness Can model the effect of length of
intervention on effectiveness
Disadvantages Requires extensive data collection,
so best where routine data are to be used
Additional time analyses only appropriate if no cluster effect or cluster x time interactions
Currently no published guide to data analysis (but watch this space!)
Review of Stepped Wedge studies
Comprehensive literature search found only 12 papers or protocols:
Lead Author Date Disease Country Setting Gambia Hepatitis Study Group
1987 Liver cancer Gambia Regions
Cook 1996 Substance abuse USA Workplace Wilmink 1999 Ruptured abdominal
aortic aneurysms UK GP surgeries
Somerville 2002 Respiratory Health UK Houses in Watcombe Fairley 2003 HIV (Adherence to
antiretroviral therapy) Australia Sexual health clinic
Hughes 2003 HIV (Mother to child transmission)
Zambia and Uganda
Health clinics
Levy 2004 HIV (Adherence to antiretroviral therapy)
Australia Ambulatory care clinic in a tertiary hospital
Priestly 2004 Critical care UK NHS hospital trust Bailey 2004 Water-borne diseases South Africa Households Grant 2005 TB in HIV+ men South Africa Company health centre Ciliberto 2005 Childhood malnutrition Malawi National rehabilitation
units Chaisson 2005 TB in HIV+ men Brazil HIV clinics
Randomisation and Sample Size
Author Level of stepping Randomised? No. Steps SS Calc reported?Intervention Control
Gambia Hepatitis Study Group
Vaccination team Yes 17 61,065 63,512Yes
Cook Cohort Yes 2 NoWilmink Individual Yes 13,147 29,713 person
years70,298 person
years NoSomerville Sets of houses Yes 2 No
Fairley Not stated Yes 43 NoHughes Pre-natal clinic Not stated 2 Aim: 304 Aim: 304 YesLevy Individual Yes Not stated NoPriestly Ward Yes – in pairs 8 2,903 4,547 YesBailey District Not stated 4 NoGrant Individual Yes 1,655 No
Ciliberto Rehab unit Not stated 7 992 186 YesChaisson Clinic Yes 29 No
4001,655
Not stated
No. Participants
371
11943
68
Reported motivations Ethical (n=4) Practical problems of simultaneous
intervention (n=4): insufficient resources (n=3); logistical difficulties (n=2)
Maintain RCT for evaluation (n=4) Detect underlying trends/control for time
(n=4) Individuals/clusters act as own controls (n=2) None (n=1)
Methods of Data AnalysisLead Author Primary outcome
measure Method(s) of Analysis
Gambia Hepatitis Study Group
Liver cancer rates/Vaccine efficacy
Comparisons of incidence rates on a step by step basis to identify vaccine efficacy
Cook Health Behaviour Questionnaire measures
Comparison of group means and group by time, gender and education interactions (F-test)
Wilmink Incidence and mortality of RAAAs
Poisson likelihood distribution for incidence rates in person years and maximum likelihood rate ratios
Somerville Respiratory Health Symptoms
Not stated (description of intervention only)
Fairley Proportion of missed doses
Unpaired t-test of means
Hughes Mother to child HIV transmission
Not stated (protocol only)
Levy Proportion of missed doses
Wilcoxon rank-sum test
Priestly Rate of in-hospital deaths
Logistic regression Cox proportional hazard models (length of stay)
Bailey Water quality Summary statistics only Time series analysis for diarrhoea rates
Grant TB episodes >90 days after clinic entry
Poisson random effects model
Ciliberto Attainment WHZ score >-2/Death
95% CI for differences between groups Linear and logistic regression for effects of covariates
Chaisson TB Incidence Step by step analysis of incidence Conditional logistic regression Cost-effectiveness analysis
Conclusions: Design Stepped wedge design has significant
potential for evaluating public policy interventions using a RCT
Intensive data collection means design most appropriate where routine data used
Opportunities for assessing different effects of time
Conclusions: Review Review highlighted dearth of evaluations
using the stepped wedge design Variety of interventions and settings
establishes design’s potential Need to ensure studies reported to same
standards as other trials (e.g. CONSORT) – particularly sample size calculations
Variety of statistical approaches to data analysis implies need for standardised approach
