Performance Evaluation of the Seoul Safety Income Project (SSIP)

Last registered on May 22, 2023


Trial Information

General Information

Performance Evaluation of the Seoul Safety Income Project (SSIP)
Initial registration date
February 16, 2023

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
February 21, 2023, 6:59 AM EST

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

Last updated
May 22, 2023, 11:17 PM EDT

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



Primary Investigator

Seoul National University

Other Primary Investigator(s)

PI Affiliation
University of Seoul
PI Affiliation
Hong Kong University of Science and Technology
PI Affiliation
University of Hong Kong

Additional Trial Information

On going
Start date
End date
Secondary IDs
Prior work
This trial does not extend or rely on any prior RCTs.
We study the effects of the Seoul Safety Income Project (SSIP) on labor market outcomes, household finance, health, education and societal behavior. In collaboration with the Seoul Metropolitan Government (SMG), we conduct a randomized controlled trial in which randomly selected households will receive a monthly income payment for three years. Monthly payments are equivalent to 50% of the difference between the household’s income and 85% of the median income. We will evaluate the impact of SSIP using detailed individual and household level information obtained from surveys and administrative data.
External Link(s)

Registration Citation

Kim, Hyuncheol et al. 2023. "Performance Evaluation of the Seoul Safety Income Project (SSIP)." AEA RCT Registry. May 22.
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Experimental Details


Households in the treatment group will receive a monthly payment corresponding to half of the difference between their income and 85% of the standard median income. Households will be subject to an income and means test on a monthly basis during the three-year period to verify their eligibility and ensure that the amounts of SSIP income they receive reflect the changes in their income and assets. Each eligible household will receive a debit card, from which they can withdraw their monthly SSIP payment.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
Primary outcomes can be categorized into three domains:
1. Economic outcomes: Labor market (employment status, work hours); Household finance (earned income, income from public transfer, income from private transfer, total expenditure, assets, debts); Housing (housing condition, housing satisfaction);
2. Health outcomes: Health (general health status, healthy eating, health behaviors, sleeping); Mental health (self-esteem, depression, stress, happiness, life satisfaction);
3. Family and Society outcomes: Family/education (family satisfaction, family conflict, attitude to marriage, fertility preference, amount of money spent on education/training and children’s education); Social behavior (social relationship, self-community interest); Receipt of other social benefits;
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Similar to primary outcomes, we categorize secondary outcomes into three domains:
1. Economics outcomes: Labor market (job search effort, determination to work, job satisfaction, willingness to work extra hours, side jobs, leisure activities); Household finance (expenditures and assets by category, financial security, charity donation); Housing (residential unit type, ownership status);
2. Health outcomes: Health (general health status by category);
3. Family and Soceity outcomes: Family/education (reeducation training program, childcare); Social behavior (donations, degree of social isolation, trust in others, types of hobbies, volunteering activities)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
SSIP recruits study households in two phases. Phase 1 started in July 2022 and Phase 2 will start in July 2023. In the first phase, 1500 households with less than 50 percent of the standard median income and assets less than USD 272,803 (≈KRW 326 million) were selected for the study sample. Among eligible applicants, 1,500 households were randomly selected, and became the study sample for Phase 1 experiment. Out of 1500 households, 500 and 1000 households were randomly assigned to the treatment group and the control group, respectively. In the second phase, 3300 additional households with less than 85 percent of the standard median income and assets less than USD 272,803 will be selected. Among eligible candidates, 3,300 households will be randomly selected, and 1,100 and 2,200 households will be randomly assigned to treatment and control groups, respectively.

We will collect information through surveys and administrative data. Study participants (of Phase 1) have already agreed to take a total of eight rounds of survey: a baseline survey before the first income payment, six rounds of follow-up surveys conducted once every six months for three years, and an endline survey one year after the income payment ends. Our research team developed survey instruments in collaboration with SMG. Household heads will be the main respondent of the surveys. We also plan to exploit administrative data on participants’ monthly labor/business income and assets level provided once a year by the Korea Social Security Information Service (SSIS). All project participants have allowed us to access their information via SSIS. Furthermore, we are able to access debit card usage records for households in the treatment group from which we may be able to infer the usage of SSIP income benefits.
Experimental Design Details
Not available
Randomization Method
We employ a stratified random sampling procedure that follows statistical criteria designed to ensure representation of the household sizes and ages that are potentially eligible for the SSIP. Stratification was based on two characteristics; household head’s age (divided into three categories – -39, 40-64, and 65+) and household size (divided into four categories – 1, 2, 3, and 4+). Randomization was conducted by SMG using a computer.
Randomization Unit
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
4,800 households (1st phase - 1500; 2nd phase - 3300)
Sample size: planned number of observations
4,800 households (1st phase - 1500; 2nd phase - 3300)
Sample size (or number of clusters) by treatment arms
3,200 households in control group and 1,600 households in treatment group.
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)
If we set the treatment effect size at 0.1 standard deviations, holding the significance level at 0.05 and treatment to control group sampling ratio at 0.5, our power calculations suggest that the sample size for achieving statistical power of 0.8 is 2,550 and for statistical power of 0.9 it is 3,414. As our estimated sample size from pooling both phases is 4,800, the power calculations suggest that the project is capable of detecting economically meaningful treatment effects on households’ outcomes.

Institutional Review Boards (IRBs)

IRB Name
IRB Approval Date
IRB Approval Number
Analysis Plan

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