This graphic displays the daily number of new COVID-19 cases, reported by the Los Angeles County Department of Public Health, along with the corresponding index of visits to retail stores and recreational activities, reported by Google Community Mobility Reports, for Los Angeles County during March 1 – June 28, 2020.
The smaller sky-blue data points show the daily counts of COVID-19 cases, measured along the left-hand vertical axis on a logarithmic scale. The larger blue data points show the corresponding weekly averages, calculated as the geometric mean.
The connected red line segments show the Google Mobility index, measured along the right-hand axis. The index is shown as a percentage of the baseline level of activity, which is calculated in relation to the median value for the 5-week period from January 3 – February 6, 2020. For example, a value of –20 would correspond to a 20 percent decline compared to baseline.
For a similar graphic relating COVID-19 case incidence to the same Google Mobility index for Broward County, Florida, see Data From the COVID-19 Epidemic in Florida Suggest That Younger Cohorts Have Been Transmitting Their Infections to Less Socially Mobile Older Adults (July 5, 2020).
The graphic should not be interpreted to mean that visits to retail stores or recreational activities are specific causes of the renewed increase in COVID-19 case counts since the week of May 17. However, the data do support the hypothesis that the upswing in case incidence is correlated with at least one indicator of social mobility.