  Ever since the first case of the novel coronavirus disease (COVID-19) was
confirmed in Wuhan, China, social distancing has been promoted worldwide,
including the United States. It is one of the major community mitigation
strategies, also known as non-pharmaceutical interventions. However, our
understanding is remaining limited in how people practice social distancing. In
this study, we construct a Social Distancing Index (SDI) to evaluate people's
mobility pattern changes along with the spread of COVID-19. We utilize an
integrated dataset of mobile device location data for the contiguous United
States plus Alaska and Hawaii over a 100-day period from January 1, 2020 to
April 9, 2020. The major findings are: 1) the declaration of the national
emergency concerning the COVID-19 outbreak greatly encouraged social distancing
and the mandatory stay-at-home orders in most states further strengthened the
practice; 2) the states with more confirmed cases have taken more active and
timely responses in practicing social distancing; 3) people in the states with
fewer confirmed cases did not pay much attention to maintaining social
distancing and some states, e.g., Wyoming, North Dakota, and Montana, already
began to practice less social distancing despite the high increasing speed of
confirmed cases; 4) some counties with the highest infection rates are not
performing much social distancing, e.g., Randolph County and Dougherty County
in Georgia, and some counties began to practice less social distancing right
after the increasing speed of confirmed cases went down, e.g., in Blaine
County, Idaho, which may be dangerous as well.
