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COVID-19

The Math Behind Social Distancing

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The math behind social distancing

The Math Behind Social Distancing

As we wait for scientists and healthcare professionals to develop a vaccine for COVID-19, there is another, more readily available tool at our disposal.

Social distancing, defined as measures taken to reduce physical contact, is the first line of defense for containing an infectious disease like COVID-19. That’s because these infections spread when people cough, sneeze, or touch surfaces on which the virus resides.

To help us grasp the impact these measures can actually have, today’s infographic illustrates how a reduction in social exposure can theoretically contain the spread of infection.

Theoretical Potential

The calculations used to create today’s infographic come from Signer Laboratory, a stem cell research lab located in the Moores Cancer Center at the University of California San Diego.

Using a summation formula makes it possible to estimate the number of new infections over a 30 day period, across three scenarios.

Scenario5 Day Period30 Day Period
No social distancing practiced1 person infects 2.5* others406 people infected as a result
50% reduction in social exposure1 person infects 1.25* others15 people infected as a result
75% reduction in social exposure1 person infects 0.625* others2.5 people infected as a result

*For estimations only. It is not possible to infect only a fraction of another person.

To arrive at the figures reported above, Robert A.J. Signer, Ph.D., and his team made a number of key assumptions.

First, they estimated the basic reproduction number (R0) of COVID-19 to be 2.5, a figure supported by recent research. This means that, on average, an infected individual will spread the disease to 2.5 other people.

Next, they assumed that an infected individual will unknowingly spread COVID-19 over the median five day incubation period. After this period, the individual will begin to develop symptoms, immediately self quarantine, and no longer pose a threat.

Finally, they assumed a direct linear correlation between social interactions and R0. This means that when an infected person reduces their physical contact with others by 50%, they also spread the disease by an amount 50% less.

Timing is Everything

While the figures above are the results of mathematical estimations, researchers have actually studied social distancing from a variety of angles.

One study used simulations to determine the magnitude and timing of social distancing measures required to prevent a pandemic. The distancing measures simulated were:

MeasureDetails
School closureTeachers and students spent weekday daytime cycles at home, rather than at school.
Increased case isolationUpon becoming symptomatic, adults (90%) and children (100%) would self quarantine for the duration of the infection.
Workplace non-attendanceEach day, a person had a 50% chance of staying home instead of attending their workplace.
Community contact reductionIndividuals reduced their physical contact with community members by half, each day.
Combination of all fourAll four measures combined. 

The results, for a community of 30,000 people and an epidemic with R=2.5, are charted below. We can define the final illness attack rate as the share of people from an at risk population who ultimately catch the disease.

power of early social distancing

Results showed that when no action was taken, 65% of the population contracted the disease. However, if a combination of all four distancing measures were implemented instead, the attack rates were:

  • 45% (distancing begins after a 4 week delay)
  • 21% (distancing begins after a 3 week delay)
  • 7% (distancing begins after a 2 week delay)

What’s clear is that social distancing was significantly more effective when implemented with minimal delay—the final illness attack rate rose quickest beyond the third week. These findings draw a parallel to the visualizations in today’s infographic, which showed us just how quickly a disease can spread.

Social distancing interventions are important as they represent the only … measure guaranteed to be available against a novel strain of influenza in the early phases of a pandemic.

Kelso, J.K., Milne, G.J. & Kelly, H., BMC Public Health 9, 117 (2009)

We arrive at a similar conclusion when it comes to the types of distancing measures implemented. In the simulations, none of the four measures taken on their own were able to have a similar effect as when they were combined.

We All Have a Part to Play

With the global number of COVID-19 cases still rising, many governments have issued quarantine orders and travel bans.

The math supports these decisions—reducing our physical contact with others, even when we aren’t experiencing any symptoms, is crucial. Studies like the one summarized above also prove that taking action sooner, rather than later, can go a long way in reducing the spread of infection.

The key takeaway from all of this? Social distancing is a powerful disease control tool, but only if we all participate.

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COVID-19

How U.S. Consumers are Spending Differently During COVID-19

How has COVID-19 transformed consumer spending trends so far? We look at credit and debit card spending of 5 million U.S. consumers across 18 categories.

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In 2019, nearly 70% of U.S. GDP was driven by personal consumption.

However, in the first quarter of 2020, the COVID-19 pandemic has initiated a transformation of consumer spending trends as we know them.

Consumer Spending in Charts

By leveraging new data from analytics platform 1010Data, today’s infographic dives into the credit and debit card spending of five million U.S. consumers over the past few months.

Let’s see how their spending habits have evolved over that short timeframe:

How U.S. Consumers are Spending Differently During COVID-19

The above data on consumer spending, which comes from 1010Data and powered by AI platform Exabel, is broken into 18 different categories:

  • General Merchandise & Grocery: Big Box, Pharmacy, Wholesale Club, Grocery
  • Retail: Apparel, Office Supplies, Pet Supplies
  • Restaurant: Casual dining, Fast casual, Fast food, Fine dining
  • Food Delivery: Food delivery, Grocery Delivery, Meal/Snack kit
  • Travel: Airline, Car rental, Cruise, Hotel

It’s no surprise that COVID-19 has consumers cutting back on most of their purchases, but that doesn’t mean that specific categories don’t benefit from changes in consumer habits.

Consumer Spending Changes By Category

The onset of changing consumer behavior can be observed from February 25, 2020, when compared year-over-year (YoY).

As of May 12, 2020, combined spending in all categories dropped by almost 30% YoY. Here’s how that shakes out across the different categories, across two months.

General Merchandise & Grocery

This segment saw a sharp spike in initial spending, as Americans scrambled to stockpile on non-perishable food, hand sanitizer, and toilet paper from Big Box stores like Walmart, or Wholesale Clubs like Costco.

In particular, spending on groceries reached a YoY increase of 97.1% on March 18, 2020. However, these sudden panic-buying urges leveled out by the start of April.

 Feb 25, 2020 YoY SpendingMay 5, 2020 YoY SpendingOverall Change
Big Box+14.2%-1.5%-15.7%
Grocery+1.0%+9.4%+8.4%
Pharmacy-3.6%-23.8%-20.2%
Wholesale Club+13.0%+2.6%-10.4%

Pharmaceutical purchases dropped the most in this segment, possibly as individuals cut back on their healthcare expenditures during this time. In fact, in an April 2020 McKinsey survey of physicians, 80% reported a decline in patient volumes.

Retail

With less foot traffic in malls and entire stores forced to close, sales of apparel plummeted both in physical locations and over e-commerce platforms.

 Feb 25, 2020 YoY SpendingMay 5, 2020 YoY SpendingOverall Change
Apparel-5.6%-51.9%-46.3%
Office Supplies-8.9%-2.8%+6.1%
Pet Supplies+2.7%-18.5%-21.2%

Interestingly, sales of office supplies rose as many pivoted to working from home. Many parents also likely required more of these resources to home-school their children.

Restaurant

The food and beverage industry has been hard-hit by COVID-19. While many businesses turned to delivery services to stay afloat, those in fine dining were less able to rely on such a shift, and spiraled by 88.2% by May 5, 2020, year-over-year.

 Feb 25, 2020 YoY SpendingMay 5, 2020 YoY ChangeOverall Change
Casual Dining-2.7%-64.9%-62.2%
Fast Casual4.2%-29.6%-33.8%
Fast Food2.0%-20.9%-22.9%
Fine Dining-18.6%-88.2%-69.6%

Applebees or Olive Garden exemplify casual dining, while Panera or Chipotle characterize fast casual.

Food Delivery

Meanwhile, many consumers also shifted from eating out to home cooking. As a result, grocery delivery services jumped by over five-fold—with consumers spending a whopping 558.4% more at its April 19, 2020 peak compared to last year.

 Feb. 25, 2020 YoY SpendingMay 5, 2020 YoY SpendingOverall Change
Food Delivery+18.8%+67.1%+48.3%
Grocery Delivery+23.0%+419.7%+396.7%
Meal/ Snack Kit+7.0%-5.9%-12.9%

Food delivery services are also in high demand, with Doordash seeing the highest growth in U.S. users than any other food delivery app in April.

Travel

While all travel categories experienced an immense decline, cruises suffered the worst blow by far, down by 87.0% in YoY spending since near the start of the pandemic.

 Feb 25, 2020 YoY SpendingMay 5, 2020 YoY SpendingOverall Change
Airline-7.7%-99.1%-91.4%
Car Rental-6.3%-86.0%-79.7%
Cruise-18.7%-105.7%-87.0%
Hotel-7.0%-85.9%-78.9%

Airlines have also come to a halt, nosediving by 91.4% in a 10-week span. In fact, governments worldwide have pooled together nearly $85 billion in an attempt to bail the industry out.

Hope on the Horizon?

Consumer spending offers a pulse of the economy’s health. These sharp drops in consumer spending fall in line with the steep decline in consumer confidence.

In fact, consumer confidence has eroded even more intensely than the stock market’s performance this quarter, as observed when the Index of Consumer Sentiment (ICS) is compared to the S&P 500 Index.

Consumer Sentiment Index

Many investors dumped their stocks as the coronavirus hit, but consumers tightened their purse strings even more. Yet, as the chart also shows, both the stock market and consumer sentiment are slowly but surely on the mend since April.

As the stay-at-home curtain cautiously begins to lift in the U.S., there may yet be hope for economic recovery on the horizon.

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Central Banks

How Global Central Banks are Responding to COVID-19, in One Chart

What policy tools are global central banks implementing to combat the economic effects of COVID-19? We compare the responses of 29 countries.

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How Global Central Banks are Responding to COVID-19

When times get tough, central banks typically act as the first line of defense.

However, modern economies are incredibly complex—and calamities like the 2008 financial crisis have already pushed traditional policy tools to their limits. In response, some central banks have turned to newer, more unconventional strategies such as quantitative easing and negative interest rates to do their work.

In response to the COVID-19 pandemic, central banks are once again taking decisive action. To help us understand what’s being done, today’s infographic uses data from the International Monetary Fund (IMF) to compare the policy responses of 29 systemically important economies.

The Central Bank Toolkit

To begin, here are brief descriptions of each policy, which the IMF sorts into four categories:

1. Monetary Policies

Policies designed to control the money supply and promote stable economic growth.

Policy NameIntended Effect
Policy rate cutsStimulates economic activity by decreasing the cost of borrowing
Central bank liquidity supportProvides distressed markets with additional liquidity, often in the form of loans
Central bank swap linesAgreements between the U.S. Fed and foreign central banks to enhance the provision of U.S. dollar liquidity
Central bank asset purchase schemesUses newly-created currency to buy large quantities of financial assets, such as government bonds. This increases the money supply and decreases longer-term rates

2. External Policies

Policies designed to mitigate the effects of external economic shocks.

Policy NameIntended Effect
Foreign currency interventionStabilizes the national currency by intervening in the foreign exchange market
Capital flow measuresRestrictions, such as tariffs and volume limits, on the flow of foreign capital in and out of a country

3. Financial Policies for Banks

Policies designed to support the banking system in times of distress.

Policy NameIntended Effect
Easing of the countercyclical capital bufferA reduction in the amount of liquid assets required to protect banks against cyclical risks
Easing of systemic risk or domestic capital bufferA reduction in the amount of liquid assets required to protect banks against unforeseen risks
Use of capital buffersAllows banks to use their capital buffers to enhance relief measures
Use of liquidity buffersAllows banks to use their liquidity buffers to meet unexpected cash flow needs
Adjustments to loan loss provision requirementsThe level of provisions required to protect banks against borrower defaults are eased

4. Financial Policies for Borrowers

Policies designed to improve access to capital as well as provide relief for borrowers.

Policy NameIntended Effect
State loans or credit guaranteesEnsures businesses of all sizes have adequate access to capital
Restructuring of loan terms or moratorium on paymentsProvides borrowers with financial assistance by altering terms or deferring payments

Putting Policies Into Practice

Let’s take a closer look at how these policy tools are being applied in the real world, particularly in the context of how central banks are battling the effects of the COVID-19 pandemic.

1. Monetary Policies

So far, many central banks have enacted expansionary monetary policies to boost slowing economies throughout the pandemic.

One widely used tool has been policy rate cuts, or cuts to interest rates. The theory behind rate cuts is relatively straightforward—a central bank places downward pressure on short-term interest rates, decreasing the overall cost of borrowing. This ideally stimulates business investment and consumer spending.

If short-term rates are already near zero, reducing them further may have little to no effect. For this reason, central banks have leaned on asset purchase schemes (quantitative easing) to place downward pressure on longer-term rates. This policy has been a cornerstone of the U.S. Federal Reserve’s (Fed) COVID-19 response, in which newly-created currency is used to buy hundreds of billions of dollars of assets such as government bonds.

When the media says the Fed is “printing money”, this is what they’re actually referring to.

2. External Policies

External policies were less relied upon by the systemically important central banks covered in today’s graphic.

That’s because foreign currency interventions, central bank operations designed to influence exchange rates, are typically used by developing economies only. This is likely due to the higher exchange rate volatility experienced by these types of economies.

For example, as investors flee emerging markets, Brazil has seen its exchange rate (BRL/USD) tumble 30% this year.

In an attempt to prevent further depreciation, the Central Bank of Brazil has used its foreign currency reserves to increase the supply of USD in the open market. These measures include purchases of $8.8B in USD-denominated Brazilian government bonds.

3. Financial Policies for Banks

Central banks are often tasked with regulating the commercial banking industry, meaning they have the authority to ease restrictions during economic crises.

One option is to ease the countercyclical capital buffer. During periods of economic growth (and increased lending), banks must accumulate reserves as a safety net for when the economy eventually contracts. Easing this restriction can allow them to increase their lending capacity.

Banks need to be in a position to continue financing households and corporates experiencing temporary difficulties.

—Andrea Enria, Chair of the ECB Supervisory Board

The European Central Bank (ECB) is a large proponent of these policies. In March, it also allowed its supervised banks to make use of their liquidity buffers—liquid assets held by a bank to protect against unexpected cash flow needs.

4. Financial Policies for Borrowers

Borrowers have also received significant support. In the U.S., government-sponsored mortgage companies Fannie Mae and Freddie Mac have announced several COVID-19 relief measures:

  • Deferred payments for 12 months
  • Late fees waived
  • Suspended foreclosures and evictions for 60 days

The U.S. Fed has also created a number of facilities to support the flow of credit, including:

  • Primary Market Corporate Credit Facility: Purchasing bonds directly from highly-rated corporations to help them sustain their operations.
  • Main Street Lending: Purchasing new or expanded loans from small and mid-sized businesses. Businesses with up to 15,000 employees or up to $5B in annual revenue are eligible.
  • Municipal Liquidity Facility: Purchasing short-term debt directly from state and municipal governments. Counties with at least 500,000 residents and cities with at least 250,000 residents are eligible.

Longer-term Implications

Central bank responses to COVID-19 have been wide-reaching, to say the least. Yet, some of these policies come at the cost of burgeoning debt-levels, and critics are alarmed.

In Europe, the ECB has come under scrutiny for its asset purchases since 2015. A ruling from Germany’s highest court labeled the program illegal, claiming it disadvantages German taxpayers (Germany makes larger contributions to the ECB than other member states). This ruling is not concerned with pandemic-related asset purchases, but it does present implications for future use.

The U.S. Fed, which runs a similar program, has seen its balance sheet swell to nearly $7 trillion since the outbreak. Implications include a growing reliance on the Fed to fund government programs, and the high difficulty associated with safely reducing these holdings.

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