Information Provision and the Timing of Subsidy Applications for Conversion to Combined Septic Tanks: A Cluster-Randomized Trial in Date City

Last registered on June 15, 2026

Pre-Trial

General Information

Title

RCT ID

AEARCTR-0018835

Initial registration date

June 06, 2026

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

June 15, 2026, 1:47 PM EDT

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

Locations

Country

Japan

Region

Date City, Fukushima Prefecture

Primary Investigator

Name

Eiji Satoh

Affiliation

Fukushima University

Contact Primary Investigator

Other Primary Investigator(s)

Additional Trial Information

Status

In development

Start date

2026-04-01

End date

2028-03-31

Keywords

Behavior, Environment & Energy, Governance

Additional Keywords

JEL code(s)

C93; Q58; Q53; L95; D83

Secondary IDs

Prior work

This trial does not extend or rely on any prior RCTs.

Abstract

This study evaluates whether low-cost information provision can encourage households with single-treatment septic tanks or night-soil collection systems to take steps toward conversion to combined septic tanks in Date City, Fukushima Prefecture. The intervention consists of leaflet inserts distributed through the municipal newsletter. The standard leaflet explains the subsidy program, consultation channels, and basic procedures, while the enhanced leaflet adds a light planning prompt encouraging households to think about when and by whom they will consult the City. The study is implemented as a parallel-arm cluster-randomized controlled trial. Constructed clusters of administrative aza units are randomly assigned to receive either the standard leaflet or the enhanced leaflet, with an initial distribution in August 2026 and a reminder in November 2026 under the same assignment. The primary outcome is the time until the first pre-construction subsidy application. Key secondary outcomes include consultation with the City and construction start. The primary analysis estimates the intention-to-treat effect of assignment to the enhanced leaflet relative to the standard leaflet using anonymized administrative records and consultation logs.

External Link(s)

Registration Citation

Citation

Satoh, Eiji. 2026. "Information Provision and the Timing of Subsidy Applications for Conversion to Combined Septic Tanks: A Cluster-Randomized Trial in Date City." AEA RCT Registry. June 15. https://doi.org/10.1257/rct.18835-1.0

Sponsors & Partners

Partner

Name

Waterworks and Sewerage Division, Construction Department, Date City

Type

municipality

URL

Experimental Details

Interventions

Intervention(s)

The intervention consists of leaflet inserts distributed through the municipal newsletter to households in areas outside the public sewer service area in Date City. The leaflets provide information on conversion from single-treatment septic tanks or night-soil collection systems to combined septic tanks, including the municipal subsidy program, consultation channels, and the basic steps required before construction starts. Clusters are assigned to receive either a standard leaflet or an enhanced leaflet. The enhanced leaflet contains the same information as the standard leaflet and additionally includes a light consultation-planning prompt encouraging households to think about when and by whom they will consult the City. The intervention does not change monetary incentives, eligibility rules, application procedures, or ordinary municipal services.

Intervention Start Date

2026-07-27

Intervention End Date

2026-10-26

Primary Outcomes

Primary Outcomes (end points)

The primary outcome is the timing of the first pre-construction subsidy application for conversion to a combined septic tank, measured as a household-by-month event indicator in the main analysis.

Primary Outcomes (explanation)

The primary outcome is constructed from municipality-provided anonymized administrative records. For each eligible household, the study will identify the first date on which a pre-construction subsidy application for conversion to a combined septic tank is recorded. The main analysis will use a household-by-month panel and define the outcome as whether household i submits its first pre-construction subsidy application in month t. Households with no recorded pre-construction subsidy application by the end of the observation window will be treated as not having experienced the event during that window, subject to the maintained assumption that administrative records were compiled according to ordinary municipal procedures. Complementary analyses will report whether the first pre-construction subsidy application occurred within 3, 6, and 12 months after the initial leaflet distribution. The main observation window is 12 months after the initial leaflet distribution. If follow-up data are extended, exploratory analyses may consider a longer window.

Secondary Outcomes

Secondary Outcomes (end points)

Key secondary outcomes are the time until first consultation with the City and the time until construction start. Exploratory and mechanism-related measures include consultation content, consultation mode, respondent category, trigger of consultation, whether the leaflet was seen, whether the enhanced planning prompt was noticed, contractor-related involvement, family- or neighbor-mediated information pathways, subsequent administrative milestones, and conversion completion where available.

Secondary Outcomes (explanation)

The key secondary outcomes are constructed from municipality-provided behavioral history records, consultation logs, and, where available, subsidy execution ledger records. Time until first consultation is based on the first recorded septic-tank-conversion-related consultation or inquiry with the City that can be linked to the household-level administrative record. Time until construction start is based on the first recorded construction start date in the administrative records or subsidy ledger. Contacts that cannot be linked rigorously to household-level records will not be used in the main household-level secondary outcomes, but may be used in supplementary descriptive or cluster-level analyses. Additional mechanism-related variables from consultation logs will be used to interpret behavioral pathways rather than as the basis for the main confirmatory claim.

Experimental Design

The study is a parallel-arm cluster-randomized controlled trial. The unit of randomization is a constructed geographic cluster based on administrative aza units in areas outside the public sewer service area in Date City. Clusters are randomly assigned to receive either the standard leaflet or the enhanced leaflet. The first leaflet is distributed through the August 2026 municipal newsletter, and the reminder leaflet is distributed through the November 2026 municipal newsletter under the same assignment. The primary estimand is the intention-to-treat effect of assignment to the enhanced leaflet relative to assignment to the standard leaflet.

Experimental Design Details

Not available

Randomization Method

The formal random assignment was conducted by computer using a pre-specified covariate-constrained randomization procedure applied to the frozen assignment input. Candidate assignments were generated under hard constraints requiring overall and district-level balance in the number of clusters assigned to each arm. Balance was evaluated using pre-specified cluster-level variables, including the number of eligible target households, the number of combined septic tank households, the number of aza units in the cluster, cluster-size indicators, the share of combined septic tank households among known septic-related households, and multi-oaza cluster status. The selected allocation was finalized before the first intervention wave and before inspection of any post-intervention outcome data.

Randomization Unit

Constructed geographic cluster based on administrative aza units.

Was the treatment clustered?

Yes

Experiment Characteristics

Sample size: planned number of clusters

247 constructed geographic clusters

Sample size: planned number of observations

6,240 eligible target households with single-treatment septic tanks or night-soil collection systems, nested in 247 randomized geographic clusters. The primary analysis uses a household-by-month panel constructed from anonymized administrative records.

Sample size (or number of clusters) by treatment arms

123 constructed geographic clusters assigned to the enhanced leaflet arm, containing 3,024 eligible target households. 124 constructed geographic clusters assigned to the standard leaflet arm, containing 3,216 eligible target households.

Minimum detectable effect size for main outcomes (accounting for sample design and clustering)

Not specified as a single value. The final design includes 6,240 eligible target households nested in 247 randomized geographic clusters. Because the primary outcome is the timing of pre-construction subsidy application, and because application events may be relatively rare in the short run, the minimum detectable effect depends strongly on the assumed baseline application rate, follow-up window, intracluster correlation, and the distribution of eligible households across clusters. The study will therefore emphasize effect sizes, confidence intervals, and policy relevance, and will supplement conventional cluster-robust inference with design-based or randomization-based inference where feasible.

Supporting Documents and Materials

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IRB

Institutional Review Boards (IRBs)

IRB Name

Fukushima University

IRB Approval Date

2026-03-19

IRB Approval Number

2025-40

Analysis Plan

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