Citizens Preferences for Direct vs Indirect Taxation: Vertical vs Horizontal Equity

Last registered on May 23, 2024


Trial Information

General Information

Citizens Preferences for Direct vs Indirect Taxation: Vertical vs Horizontal Equity
Initial registration date
July 25, 2022

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
July 26, 2022, 1:59 PM EDT

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

Last updated
May 23, 2024, 11:00 AM EDT

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



Primary Investigator


Other Primary Investigator(s)

PI Affiliation
PI Affiliation
PI Affiliation

Additional Trial Information

Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
A large share of the workforce works in self-employed in developing countries, a hard to tax segment, compared to salaried employees. We study the perception of fairness of the tax system, focusing on the horizontal inequity between salaried and self-employed individuals, in five large low and middle-income countries. We conjecture that the prevalence of self-employment, strengthens horizontal equity concerns, which in turn lowers demand for tax interventions, and especially direct income taxation. To test this hypothesis, we conduct online surveys eliciting individual perception on horizontal equity, tax fairness, relation to vertical equity and how these preferences relate to the tax instruments used by their governments. To test whether increased awareness of horizontal inequity affects tax preferences, we conduct a within-survey information treatments aimed at increasing the salience of this issue.
External Link(s)

Registration Citation

Bachas, Pierre et al. 2024. "Citizens Preferences for Direct vs Indirect Taxation: Vertical vs Horizontal Equity." AEA RCT Registry. May 23.
Experimental Details


We administer an online survey to respondents across five countries eliciting their perceptions on horizontal tax equity regarding the gap in income tax collection between self-employed and salaried workers. During the survey, we show information about the proportion of tax contributions from self-employed versus salaried workers to a random subset of respondents, to test whether receiving this information influences their views regarding the horizontal fairness of the tax system.

We compare perceptions of horizontal fairness to vertical fairness, and enquire how these preferences relate to preferences for different tax instruments (direct vs indirect) and if respondents support tax policies aimed at reducing horizontal inequity.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Tax preferences, views on the role of the tax system, perceptions regarding horizontal equity between self-employed and employees in taxation, preferences regarding vertical vs horizontal inequity, and support for different types of tax instruments (direct vs indirect). These outcomes correspond to questions in the survey instrument and their use is detailed in the pre-analysis-plan.
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
An information treatment will be administered during the online survey. The study sample will be split two treatment arms (T1: 30% and T2: 30%) and a control group (40%). The first treatment group (T1) will receive information about the share of tax revenue paid by self-employed workers in comparison to salaried employees in the country survey the survey is administered in. The second treatment group (T2) will receive the same information as T1 and an additional pedagogical treatment containing information on the contributors of the income tax and consumption tax. The survey experiment aims to raise awareness of self-employed employee tax gaps (saliency of horizontal equity) via T1 and T2 and clarify the link between equity concepts of tax instruments (T2).
Experimental Design Details
Randomization Method
Done on the computer by an online survey firm.
Randomization Unit
Individual Respondent
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
Sample size: planned number of observations
13,500, corresponding to 2,700 respondents in each of 5 countries
Sample size (or number of clusters) by treatment arms
1,100 respondents in control, 700 in T1, 700 in T2 for each of the 5 countries.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)

Institutional Review Boards (IRBs)

IRB Name
IRB Approval Date
IRB Approval Number
Analysis Plan

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Post Trial Information

Study Withdrawal

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Is the intervention completed?
Data Collection Complete
Data Publication

Data Publication

Is public data available?

Program Files

Program Files
Reports, Papers & Other Materials

Relevant Paper(s)

Reports & Other Materials