Study finds lockdowns effective at reducing travel in Sierra Leone

July 31, 2021

In recent findings, MIT researchers, in collaboration with Sierra Leone’s government, use cell tower records in Sierra Leone to show that people were traveling less during lockdowns.A proxy for mobility: cell tower recordsAny time someone’s cellphone sends or receives a text, or makes or receives a call, the nearest cell tower is pinged.These measurements showed that, on average, people were traveling less during lockdowns than before lockdowns.The data MIT and DSTI received was anonymized — an essential part of ensuring the privacy of the individuals whose data was used.So the towers pinged by a specific phone might actually represent the movement of several people, and not everyone’s movement will be captured by cell towers.

Throughout the Covid-19 pandemic, governments have used data on people’s movements to inform strategies for containing the spread of the virus. In Europe and the United States, for example, contact-tracing apps have used Bluetooth signals in smartphones to alert people when they’ve spent time near app users who have tested positive for Covid-19. 

But how can governments make evidence-based decisions in countries where such fine-grained data isn’t available? In recent findings, MIT researchers, in collaboration with Sierra Leone’s government, use cell tower records in Sierra Leone to show that people were traveling less during lockdowns. “When the government implemented novel three-day lockdowns, there was a dual aim to reduce virus spread and also limit social impacts, like increased hunger or food insecurity,” says Professor Lily L. Tsai, MIT Governance Lab’s (MIT GOV/LAB) director and founder. “We wanted to know if shorter lockdowns would be successful.”   

The research was conducted by MIT GOV/LAB and MIT’s Civic Data Design Lab (CDDL), in partnership with Sierra Leone’s Directorate for Science, Innovation and Technology (DSTI) and Africell, a wireless service provider. The findings will be published as a chapter in the book “Urban Informatics and Future Cities,” a selection of research submitted to the 2021 Computational Urban Planning and Urban Management conference. 

A proxy for mobility: cell tower records

Any time someone’s cellphone sends or receives a text, or makes or receives a call, the nearest cell tower is pinged. The tower collects some data (call-detail records, or CDRs), including the date and time of the event and the phone number. By tracking which towers a certain (anonymized) phone number pings, the researchers could approximately measure how much someone was moving around.  

These measurements showed that, on average, people were traveling less during lockdowns than before lockdowns. Professor Sarah Williams, CDDL’s director, says the analysis also revealed frequently traveled routes, which “allow the government to develop region-specific lockdowns.” 

While more fine-grained GPS data from smartphones paint a more accurate picture of movement, “there just isn’t a systematic effort in many developing countries to build the infrastructure to collect this data,” says Innocent Ndubuisi-Obi Jr., an MIT GOV/LAB research associate. “In many cases, the closest thing we can use as a proxy for mobility is CDR data.”

Measuring the effectiveness of lockdowns

Sierra Leone’s government imposed the three-day lockdown, which required people stay in their homes, in April 2020. A few days after the lockdown ended, a two-week inter-district travel ban began. “Analysis of aggregated CDRs was the quickest means to understanding mobility prior to and during lockdowns,” says Michala Mackay, DSTI’s director and chief operating officer. 

The data MIT and DSTI received was anonymized — an essential part of ensuring the privacy of the individuals whose data was used. 

Extracting meaning from the data, though, presented some challenges. Only about 75 percent of adults in Sierra Leone own cellphones, and people sometimes share phones. So the towers pinged by a specific phone might actually represent the movement of several people, and not everyone’s movement will be captured by cell towers. 

Furthermore, some districts in Sierra Leone have significantly fewer towers than others. When the data were collected, Falaba, a rural district in the northeast, had only five towers, while over 100 towers were clustered in and around Freetown, the capital. In areas with very few towers, it’s harder to detect changes in how much people are traveling. 

Since each district had a unique tower distribution, the researchers looked at each district separately, establishing a baseline for average distance traveled in each district before the lockdowns, then measuring how movement compared to this average during lockdowns. They found that travel to other districts declined in every district, by as much as 72 percent and by as little as 16 percent. Travel within districts also dropped in all but one district. 

The source of this news is from Massachusetts Institute of Technology

Popular in Research

1

1 week ago

Successful mapping raises hope of reintroducing eastern quoll to mainland Australia

2

1 week ago

University receives $2.7 million in funding to focus on regional innovation

3

6 days ago

New tool estimates how much affordable housing a city needs

4

6 days ago

Helping children with autism and hyperlexia learn to understand what they read

5

6 days ago

Freshwater ecosystems at risk due to glyphosate use

A new hub for MIT innovation and entrepreneurship

2 days ago

English Language Studies joins Comparative Media Studies/Writing

2 days ago

U.S., Australia and UK unveil new security partnership as China expands its military and influence

12 minutes ago

Reflecting on September 11, 20 years later

4 hours ago

Producer inflation accelerated in August, as wholesale prices rose record 8.3% from a year ago

6 days ago

European power companies face €114 billion ‘debt trap’ if they delay climate action

6 days ago