Reconciling Scientific Rigour with

the Service Imperative

15/05/2015

Society for Clinical Trials Conference

Arlington, VA

May 17th 2015

Professor Richard Lilford

Collaborations for Leadership in

Applied Health Research Care

Hospital

Primary Care

Local Authority

Intervention

Development

Evaluation

£20m £10m

Step Wedge Design

• What?

• Why?

Today’s talk: trials Cluster

What is a Step Wedge Design?

Hemming, Lilford & Girling. Stat Med. 2015; 34(2): 181-96.

Cluster exposed to intervention

Cluster unexposed to intervention (control)

Time

1

2

3

4

5

6

Clu

ste

r

Many variations on a theme

What is the Counter-factual?

Two Types of Cluster Study:

Cross-sectional

Cohort

Why Consider a SWD, rather than

Parallel Cluster Trial?

1. Ethics

2. Acceptability

3. Logistics

• Sample size

• Interaction between

intervention effect and time

Co-exist

4. Scientific Reasons

Disadvantages of SWDs?

Always

Analytically

complex

Sometimes

Violation of

sequence

Increase trial

duration

Long gap

between

intervention &

outcome

Spurious

All cluster

studies

Step Wedge Trials vs.

Step Wedge Studies

Time

Clu

ste

r 1

2

3

4

5

6

7

8

But may be “instrumental variable”

Naturalistic SWD

= Instrumental variable approach

The End