Opportunities for evaluation using the Stepped Wedge trial

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 n n 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 n n 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

When is the design useful? n n n 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 n n n 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 n n n 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 n Comprehensive literature search found only 12 papers or protocols:

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

Reported motivations n n n 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 Analysis

Conclusions: Design n 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 n n 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

Questions? Celia Brown: c. a. brown@bham. ac. uk 0121 414 6043 3" Wide Stepped Wedge