Nudging Take-up of $1 Health Insurance Plans

Last registered on July 05, 2021


Trial Information

General Information

Nudging Take-up of $1 Health Insurance Plans
Initial registration date
January 14, 2021
Last updated
July 05, 2021, 8:14 PM EDT


Primary Investigator

Covered California

Other Primary Investigator(s)

Additional Trial Information

Start date
End date
Secondary IDs
With the termination of Cost-Sharing Reduction (CSR) subsidies in 2017, many individuals in California's ACA Marketplace became eligible for $1 plans. But not all individuals eligible for $1 plans select the most generous coverage option for which they're eligible, thereby enrolling in a low actuarial value plan when a higher actuarial value plan is available for the same (or lower) price.

This project's goal is to examine whether an informational email can increase $1 CSR Silver take-up among Covered California households enrolled in Bronze, Gold or Platinum plans for the 2021 coverage year.

Choice errors are common across different health insurance markets--including Medicare, employer-sponsored insurance and the ACA Marketplaces--and thus identifying ways to improve choice quality is of interest to policymakers both in California and nationwide.
External Link(s)

Registration Citation

Feher, Andrew. 2021. "Nudging Take-up of $1 Health Insurance Plans." AEA RCT Registry. July 05.
Experimental Details


The intervention centers on $1 CSR Silver-eligible members who selected a Bronze, Gold or Platinum plan during the 2021 Open Enrollment period. In the final weeks of the Open Enrollment period, these Covered California members will receive an email nudge that encourages them to switch metal tiers (from Bronze, Gold or Platinum to CSR Silver) so as to pay less when accessing care. They are further encouraged to take action by 1/31/2021, the end of the 2021 Open Enrollment period.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Our primary outcome will be an indicator for whether a household enrolled in a CSR Silver plan for the 2021 coverage year by the end of the Open Enrollment period.
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary outcomes include net premium and calls to Covered California's Service Center.
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
This is a 2-arm block randomized design. The two blocks are (1) $1/month Silver 87-eligibles in Bronze or Gold plans and (2) $1/month Silver 94-eligibles in Bronze, Gold or Platinum plans.

Within each block, households are randomly assigned to one of two arms: (1) a control group or (2) an informational email group.
Experimental Design Details
Randomization Method
We used Stata to carry out the randomization.
Randomization Unit
Random assignment occurs at the household-level.
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
Sample size: planned number of observations
Approximately 5,600 households
Sample size (or number of clusters) by treatment arms
Approximately 50% of households were assigned to a control group and the remaining 50% were assigned to the informational email.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
To arrive at an estimate for the minimum detectable effect (MDE)—and given that enrollees have a little more than one week to take action—we assume a baseline metal tier switch rate of 5 percent. In a pairwise comparison, we’d be powered at the 80% level to detect a 1.8 percentage point difference in Enhanced Silver enrollment rates.

Institutional Review Boards (IRBs)

IRB Name
California Health and Human Services Agency Committee for the Protection of Human Subjects
IRB Approval Date
IRB Approval Number
Analysis Plan

Analysis Plan Documents

Pre-analysis plan

MD5: 55e15bec7bdb3c787497ddb21549a70c

SHA1: 02e7aef2c52095f1cb771006eb6b08a901ceccdf

Uploaded At: January 16, 2021


Post Trial Information

Study Withdrawal

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Is the intervention completed?
Intervention Completion Date
January 31, 2021, 12:00 +00:00
Data Collection Complete
Data Collection Completion Date
January 31, 2021, 12:00 +00:00
Final Sample Size: Number of Clusters (Unit of Randomization)
Was attrition correlated with treatment status?
Final Sample Size: Total Number of Observations
5,660 households.
Final Sample Size (or Number of Clusters) by Treatment Arms
2,830 per arm.
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials