Trends in Social Distancing

I came across some interesting data while researching the coronavirus. Social contact is a key factor in explaining the disease's spread. About a week or two before the shutdowns, social contact fell dramatically. After a while, it started to rise, but it is still well below normal. Ideally, we would track everyone and measure how many times they got within 6 feet of someone else, weighted by the amount of time that they were in close contact. That data does not exist. There is measurement error in the available data. However, all my sources tell the same story. That's why I think this pattern is real.

My first source is the Device Exposure Index (DEX) (link to the methodology). It uses smartphone location data. When you go to a store, how many other devices were in that store? One issue is that if someone stays at home, their smartphone drops out of the sample. The Adjusted DEX fixes that problem. I averaged the Adjusted DEX across all US counties, weighting by population. 

The big drop that you see is March 11. That is when the WHO declared pandemic. Shutdowns did not begin until a week or two later, but people had already started social distancing. The average value for the Adjusted DEX plummets from around 200 to roughly 50. It's about 100 now, so life is still very far from normal. 

My next data source is the Department of Transportation (link). It uses smartphone data to count how many times people leave their homes and how far that they travel. I calculated trips per person for each county. Then I averaged across all counties, weighting by population. I was surprised to see that the average person took almost 4 trips per day before the pandemic. That seems suspiciously high. But then I looked into the methodology. Each time you go somewhere, that is counted as a separate trip. So if you (1) grab coffee from Starbucks in the morning and then (2) go to work and (3) take a walk after lunch and (4) buy groceries on the way home, that is counted as 4 different trips. 

A similar pattern emerges. A big drop that preceded the shutdowns, then a gradual recovery, but it's still far below January and February. June 1 corresponds to Ndate=22067, and we see the protests showing up in the graph.

My last source is data from SafeGraph (downloaded from Carnegie Mellon: link). If a smartphone leaves the house for 3-6 hours, they assume you are working part-time. If it's away for 6+ hours, then it's full-time.

Part-time:

Full-time:

The numbers are suspiciously low. Back in February, only 9% of people worked full-time and 13% worked part-time? That can't be right. I almost threw out this dataset due to the measurement error. However, it might still have some uses. It does display the same trend: social distancing began a week or two before the shutdowns. Contact starts rising again, but it's far from normal. 

Social distancing began voluntarily, but that doesn't prove that government policies were unnecessary. Right now, I'm studying optimal policy. No results yet - just sharing some data that I found along the way. Take care