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Simplifying police bail notices to increase court attendance
Last registered on January 14, 2021


Trial Information
General Information
Simplifying police bail notices to increase court attendance
Initial registration date
January 13, 2021
Last updated
January 14, 2021 11:56 AM EST
Primary Investigator
The Behavioural Insights Team
Other Primary Investigator(s)
PI Affiliation
The Behavioural Insights Team
PI Affiliation
New Zealand Police
PI Affiliation
The Behavioural Insights Team
Additional Trial Information
Start date
End date
Secondary IDs
In 2018, the New Zealand government promised to reduce the prison population by 30% within the next 15 years. This goal arose because of recent increases in the number of prisoners, and because New Zealand has one of the highest incarceration rates in the OECD. One way to reduce the prison population and increase the efficiency of the justice system is to increase the number of people who appear in court when released on Police bail.

In this trial, the Behavioural Insights Team has partnered with New Zealand Police to test whether a behaviourally-informed new police bail notice can increase court attendance by defendants. The new notice draws on concepts from behavioural science to encourage behaviour change, including simplification, reciprocity and social norms.
External Link(s)
Registration Citation
Chappell, Nathan et al. 2021. "Simplifying police bail notices to increase court attendance ." AEA RCT Registry. January 14. https://doi.org/10.1257/rct.7018-1.0.
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Experimental Details
The intervention draws on elements of the re-design of apprehended domestic violence orders (ADVOs) by BIT in Australia, and by the re-design of court appearance notices for minor misdemeanors by ideas42 in New York. The most important elements of the intervention are:

1) Simplification: The new notice puts the most important information at the top of the document, uses simpler and more direct language, and includes the address of the court in addition to relevant phone numbers and URLs to make it easy for defendants to get more information.

2) Social norms: The new notice uses social norms by telling defendants that most people like them appear in court when necessary. Social norms have been proven effective in a number of domains, including a recent trial in New Zealand getting people to pay their fines on time.
Intervention Start Date
Intervention End Date
Primary Outcomes
Primary Outcomes (end points)
Whether a defendant appears in court at the required date and time after release on police bail
Primary Outcomes (explanation)
Secondary Outcomes
Secondary Outcomes (end points)
Secondary Outcomes (explanation)
Experimental Design
Experimental Design
The trial takes the form of a 2-armed, clustered randomised controlled trial with randomisation at the custody officer level and stratification by custody team, using six police stations as trial partners.
Experimental Design Details
Randomization Method
Randomisation in this trial is done using the 'stratified' function within the 'splitstackshape' package in R, to randomise custody officers into the treatment or control arm within each stratum (with custody teams being the strata).
Randomization Unit
Randomisation is clustered at the custody officer level.
Was the treatment clustered?
Experiment Characteristics
Sample size: planned number of clusters
131 custody officers
Sample size: planned number of observations
1000 defendants
Sample size (or number of clusters) by treatment arms
66 treatment custody officers, 65 control custody officers
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
IRB Name
IRB Approval Date
IRB Approval Number
Post Trial Information
Study Withdrawal
Is the intervention completed?
Is data collection complete?
Data Publication
Data Publication
Is public data available?
Program Files
Program Files
Reports, Papers & Other Materials
Relevant Paper(s)