Communication, Search, and Mobile Phones: A Telephone Directory Intervention in Tanzania

Last registered on August 10, 2021


Trial Information

General Information

Communication, Search, and Mobile Phones: A Telephone Directory Intervention in Tanzania
Initial registration date
August 07, 2021

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
August 10, 2021, 2:13 PM EDT

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


Primary Investigator

Cornell University

Other Primary Investigator(s)

PI Affiliation
Tufts University
PI Affiliation
UC Berkeley

Additional Trial Information

On going
Start date
End date
Secondary IDs
The expansion of information and communications technology (ICT) throughout the developing
world is among the most profound instances of technological change in modern economic history.
Yet, for all the promise of this technological transformation, our understanding of the economic
significance of these changes remains surprisingly rudimentary. This is particularly the case
regarding the potential for ICT to provide pathways out of rural poverty.
We propose to study the extent to which maize farmers in Tanzania directly benefit from an
exogenous reduction in the cost of searching for firms relevant for agricultural production or trade.
Our primary intervention is a telephone directory that lists contact information for enterprises. The
rationale is simple: while phones reduce the costs of communicating with known contacts, it is not
clear how households can expand their existing networks without complementary goods that lower
the cost of using ICT to search for new contacts.
Because this intervention generates an exogenous increase in firm exposure, we will
measure impacts on both households that receive the directory and firms that are listed. Our
findings will contribute to the understanding of both smallholder market participation and SME
performance in an era of rapidly changing information and communication technologies.
External Link(s)

Registration Citation

Aker, Jenny, Joshua Blumenstock and Brian Dillon. 2021. "Communication, Search, and Mobile Phones: A Telephone Directory Intervention in Tanzania." AEA RCT Registry. August 10.
Sponsors & Partners

There is information in this trial unavailable to the public. Use the button below to request access.

Request Information
Experimental Details


Our primary intervention is a telephone directory that lists contact information for enterprises in eight sectors relevant to agriculture. The RCT is two-sided. We randomized enterprises into trial versions of the directory at the subvillage-sector level, and we randomize distribution of the directory to households at the village level. For the enterprises, treatment is defined as being listed. For the households, treatment is defined as receiving a copy of the directory.
Intervention Start Date
Intervention End Date

Primary Outcomes

Primary Outcomes (end points)
On the enterprise side: communication (incoming calls, missed calls, calls from new customers, SMS messages), mobile money usage, employment, sales, revenue

On the household size: communication (making calls, sending texts), search outside the village, using the phone for search, mobile money usage, agricultural inputs and outputs, crop sales prices, livestock sales and purchases, ownership of non-farm enterprises
Primary Outcomes (explanation)

Secondary Outcomes

Secondary Outcomes (end points)
Secondary Outcomes (explanation)

Experimental Design

Experimental Design
We began this two-sided randomized control trial (RCT) with a census of all enterprises in eight sectors relevant to farming households. The census covered 1,494 enterprises operating in 49 villages and cities in a roughly 5,000 square mile area. We randomly selected a little over half of these enterprises to be listed in a printed phone book. The phonebook was organized by location and sector, and contained information on each enterprise's priority goods and services, which allowed for differentiation and specialization. During the next planting season we distributed 3,290 printed phone directories via community meetings in randomly selected villages. Because of the high likelihood of spillovers through directory sharing, we randomized distribution at the village level. The experiment then ran for nearly one year, covering a full cycle of agricultural activities.
Experimental Design Details
Randomization Method
Randomization was done in an office, on a computer
Randomization Unit
On the enterprise side, enterprises were first randomized into "pure control" or "other" at the village level. The "other villages" were then randomized into treatment or control at the subvillage-sector level.

On the household side, we randomized villages into treatment and control.
Was the treatment clustered?

Experiment Characteristics

Sample size: planned number of clusters
Enterprise side: 49 villages for the first stage randomization, 437 subvillage-sectors for the second stage randomization

Household side: 99 villages
Sample size: planned number of observations
Enterprise side: 440 enterprises Household side: 831 households
Sample size (or number of clusters) by treatment arms
Enterprise side (among the surveyed): 141 subvillage-sectors in treatment, 82 subvillage-sectors in control, 34 subvillage-sectors in pure control

Household side (among the surveyed): 36 villages in treatment, 34 villages in control
Minimum detectable effect size for main outcomes (accounting for sample design and clustering)

Institutional Review Boards (IRBs)

IRB Name
University of Washington Human Subjects Review
IRB Approval Date
IRB Approval Number


Post Trial Information

Study Withdrawal

There is information in this trial unavailable to the public. Use the button below to request access.

Request Information


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