A field experiment with Camden's Shape Up programme - presentation at the Faculty of Public Health annual conference 2016

1. Can commitment contracts promote
attendance and weight loss?
A field experiment with Camden’s Shape Up
programme
Presentation for Faculty of Public Health
Brighton, 14th June 2016
Manu Savani
PhD Candidate
University College London

2. How could clients be
nudged towards
improved attendance
and weight loss?
(without financial incentives)
My research question:
Could commitment
contracts help?
Partnership with Camden
Problem:
• Attendance rates tailed off over the 11-week Shape Up
programme.
• Dropping out was a barrier to weight loss success.
Solution:
Could a “commitment contract”
help clients stay focused on their
health goals and complete the
programme?
(Strotz, 1956; Thaler and Shefrin, 1981; Bryan et al 2010)
2

3. Why a commitment contract?
Make a
pledge
More
commitment,
bind future
choices
Less likely to
quit,
procrastinate,
or succumb
to temptation
Better health
behaviours
and outcomes
3
Evidence suggests financial and reputational commitment
devices does cause weight loss, but commitment contracts are
relatively untested
• (Volpp et al, 2008; Nyer and Dellande, 2010; Prestwich et al 2012)

4. A field trial to test the
impact of a commitment contract
Shape Up
clients
willing to
participate
No contract
Contract
Weekly
classes
continue as
normal
Face-to-face
recruitment
in class
Randomly
assigned
groups
Final
weigh-in
Data collected on weight
loss and attendance,
follow-up interviews
1 2 3
Half the clients sign
and take home a
commitment contract
Tutors are blind
to treatment
status
4
Compare
groups
5
Compare
differences
across groups
recruitment intervention data gatheringprogramme delivery analysis
4

5. Who took part in the study?
268
approached
208
registered
11 excluded on health
or admin grounds
97 offered
contract
100 no
contract
197
participated
Weight 82kg
BMI 31
Female 84%
Age 47
Wellbeing 6.4
GP referral 34%
Weight 85kg
BMI 31
Female 83%
Age 50
Wellbeing 6.3
GP referral 30%
• Study took place over Jan
2014 – March 2016 in 4
distinct waves, with 27
groups across 5 venues and 8
tutors
• Ex ante power calcs required
sample of around 200
5

6. Results (1)
Did the contract improve participation?
Yes: signing a contract makes it more likely a client will
complete the programme.
6
77%
69%
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Proportion of Completers
N=197, 95% CI bars
No
contract
Contract

7. Results (2)
Did the contract boost weight loss?
No: those who signed a contract lost about the same
amount of weight, on average.
Weight loss
outcomes
Last available
weigh-in (kg)
Last weigh-in after
week 7 (kg)
Last weigh-in
after week 9 (kg)
Met the 5%
weight loss target
Lost any
weight
No contract 1.9 2.3 2.5 16% 81%
Contract 2.1 2.2 2.5 19% 82%
Number of
observations
197 161 127 197 197
The averages hide a wide range of experiences:
• Some clients lost up to 15kgs
• Others gained up to 7kg.

8. Results (3)
Who benefitted most from the contract?
Female clients
Clients who missed the introductory session
Clients reporting a short-termist or fatalist attitude to
their health
Clients referred by their GP
8
Among the 96 clients who signed a commitment
contract, it was best at raising attendance for:

9. Results (4)
How did people use their contracts?
• Some clients embraced the contract, put it somewhere they
saw it every day and found it very helpful
• Others did not feel the need for it
I put it on my
fridge…and it
will continue
to be there
It wasn’t on
the top of my
mind
The contract
was an element
of self discipline
I completely
forgot about
using it…I felt I
was already
highly motivated
9
You’ve got
something in
writing…keeps
reminding you if
you do slip upYou sign a contract,
it’s binding. You
have to do
something about it

10. Are commitment contracts worthwhile?
Yes: adherence to Shape
Up programme
improved
Attendance higher by
6%, completion rates by
12%, amongst those
signing contract
Suggesting more
frequent self-monitoring
and better uptake of
course content
Cheap, simple, and
potentially cost effective
design addition to public
health programmes that
rely on consistent
participation
But: no direct impact on
weight loss
As designed, the
commitment contract was
not strong enough to
outweigh complex,
competing factors that
limited weight loss for
many clients (e.g. illness,
work and family demands)
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Many clients enjoyed the
contract, or applied their own
commitment strategies. The
principle is sound, but design
matters…

11. Recommendations
To get the most out of a commitment contract embedded in a
public health programme:
Increase salience of the commitment contract
• Co-design the contract with client, tailoring it to their personal goals and
preferences
• Tutor witnesses signing of the contract at beginning of programme , and
encourages them to place it somewhere visible
• Tutor reaffirms the contract midway through programme
Target contract at those who would benefit most
• Use simple surveys to identify if clients are more likely to have a short-
termist outlook to their health, they may benefit more
• Use the contract to plug motivational gaps
• among those who are GP-referred rather than self-referred, or those who miss an early
session that emphasizes the importance of regular participation, or those who appear to
be flagging as the course progresses
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