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Opportunities for evaluation using the Stepped Wedge trial design

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

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Opportunities for evaluation using the Stepped Wedge trial design

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  1. Opportunities for evaluation using the Stepped Wedge trial design Celia Brown, Alan Girling, Prakash Patil and Richard Lilford Department of Public Health and Epidemiology

  2. 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

  3. 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

  4. 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)

  5. 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

  6. 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!)

  7. Review of Stepped Wedge studies • Comprehensive literature search found only 12 papers or protocols:

  8. Randomisation and Sample Size No. Participants Author Level of stepping Randomised? No. Steps SS Calc reported? Intervention Control Gambia Hepatitis Vaccination team Yes 17 61,065 63,512 Study Group Yes Cook Cohort Yes 2 371 No Wilmink Individual Yes 13,147 29,713 person 70,298 person years years No Somerville Sets of houses Yes 2 119 No Fairley Not stated Yes 43 43 No Hughes Pre-natal clinic Not stated 2 Aim: 304 Aim: 304 Yes Levy Individual Yes Not stated 68 No Priestly Ward Yes – in pairs 8 2,903 4,547 Yes Bailey District Not stated 4 400 No Grant Individual Yes 1,655 1,655 No Ciliberto Rehab unit Not stated 7 992 186 Yes Chaisson Clinic Yes 29 Not stated No

  9. 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)

  10. Methods of Data Analysis

  11. 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

  12. 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

  13. Questions? Celia Brown: c.a.brown@bham.ac.uk 0121 414 6043

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