On the Impact of Social Comparison on Physician Behavior

Last registered on December 08, 2025

Pre-Trial

Trial Information

General Information

Title
On the Impact of Social Comparison on Physician Behavior
RCT ID
AEARCTR-0004747
Initial registration date
September 25, 2019

Initial registration date is when the trial was registered.

It corresponds to when the registration was submitted to the Registry to be reviewed for publication.

First published
September 25, 2019, 3:06 PM EDT

First published corresponds to when the trial was first made public on the Registry after being reviewed.

Last updated
December 08, 2025, 8:18 AM EST

Last updated is the most recent time when changes to the trial's registration were published.

Locations

Region

Primary Investigator

Affiliation
University of Bern

Other Primary Investigator(s)

PI Affiliation
University of Bern
PI Affiliation
Erasmus University Rotterdam
PI Affiliation
Erasmus University Rotterdam

Additional Trial Information

Status
Completed
Start date
2019-11-01
End date
2021-09-01
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
Abstract
Primed by the ongoing political and academic debate about rising health costs and the over-provision of medical care in the developed world, this research project strives at gaining an in-depth understanding about how the provision of social comparison information influences physician behavior, adherence to clinical guidelines and quality of care. To this end, we are planning to run a pragmatic randomized trial in which general practitioners (GPs) from the universe of all GPs active in the outpatient sector in Switzerland are randomly assigned to either an intervention group receiving social comparison letters or the control group (no letter). The information in the social comparison letters is extracted from routinely collected insurance claims data and contains information about the health care costs or practice style behavior (e.g. vaccination rate, generic drug use) of a GP in comparison to peers with a comparable risk pool of patients. Previous studies have shown that peer comparison information has the potential to significantly influence individual decision-making in various contexts thereby motivating the extension to the proposed physician population (e.g. Meeker et al., 2016; Allcott & Rogers, 2014).
External Link(s)

Registration Citation

Citation
Gerfin, Michael et al. 2025. "On the Impact of Social Comparison on Physician Behavior." AEA RCT Registry. December 08. https://doi.org/10.1257/rct.4747-1.2
Experimental Details

Interventions

Intervention(s)
We randomly assigned general practitioners (GPs) from the universe of all primary care providers active in the outpatient sector in Switzerland to receive peer comparison letters containing information on low-value care (i.e., vitamin D testing and generic substitution) or medical spending in comparison to GPs with a comparable risk pool of patients. Primary care providers in the control group receive no social comparison letter.

The letter will be sent out once at the beginning of the intervention period and the short-term reaction is tracked after half a year. To capture the long-term response, information on the main outcomes will be gathered again after one year.
Intervention (Hidden)
Intervention Start Date
2020-01-06
Intervention End Date
2020-02-03

Primary Outcomes

Primary Outcomes (end points)
Primary outcomes of the field experiment are the health care costs (plus cost subcategories) and low-value care services including vitamin D tests and the share of generics prescribed to patients of GPs active in the Swiss outpatient sector.
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
Nation-wide pragmatic randomized trial using a full factorial design allocating physicians to either the control or one of the intervention arms receiving peer comparison information.
Experimental Design Details
Randomization Method
Randomization done in office by a computer
Randomization Unit
Individual level: Primary care providers active in the Swiss outpatient sector
Was the treatment clustered?
No

Experiment Characteristics

Sample size: planned number of clusters
3064 primary care providers (n = 766 per arm)
Sample size: planned number of observations
3064 primary care providers (n = 766 per arm)
Sample size (or number of clusters) by treatment arms
766 GPs in the control group (no letter); 766 GPs in the generic substitution arm; 766 GPs in the vitmamin D testing arm and 766 in the health spending intervention group
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
IRB

Institutional Review Boards (IRBs)

IRB Name
WISO Faculty's ethics committee (University of Bern)
IRB Approval Date
2018-05-31
IRB Approval Number
N/A
Analysis Plan

Analysis Plan Documents

Study Protocol & Statistical Analysis Plan

MD5:

SHA1:

Uploaded At: December 08, 2025

Post-Trial

Post Trial Information

Study Withdrawal

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Intervention

Is the intervention completed?
No
Data Collection Complete
Data Publication

Data Publication

Is public data available?
No

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials