# SafeGraph

This data source uses data reported by SafeGraph using anonymized location data from mobile phones. SafeGraph provides several different datasets to eligible researchers. We surface signals from two such datasets. This dataset is no longer updated after April 19th, 2021.

1. SafeGraph Social Distancing Metrics

## SafeGraph Social Distancing Metrics

• Earliest issue available: June 20, 2020
• Number of data revisions since June 23, 2020: 1
• Date of last change: November 3, 2020

Data source based on social distancing metrics. SafeGraph provides this data for individual census block groups, using differential privacy to protect individual people’s data privacy.

Delphi creates features of the SafeGraph data at the census block group level, then aggregates these features to the county and state levels. The aggregated data is freely available through the COVIDcast API.

For precise definitions of the quantities below, consult the SafeGraph social distancing metric documentation.

Signal Description
completely_home_prop The fraction of mobile devices that did not leave the immediate area of their home (SafeGraph’s completely_home_device_count / device_count)
Earliest date available: 01/01/2019
full_time_work_prop The fraction of mobile devices that spent more than 6 hours at a location other than their home during the daytime (SafeGraph’s full_time_work_behavior_devices / device_count)
Earliest date available: 01/01/2019
part_time_work_prop The fraction of devices that spent between 3 and 6 hours at a location other than their home during the daytime (SafeGraph’s part_time_work_behavior_devices / device_count)
Earliest date available: 01/01/2019
median_home_dwell_time The median time spent at home for all devices at this location for this time period, in minutes
Earliest date available: 01/01/2019
completely_home_prop_7dav Offers a 7-day trailing window average of the completely_home_prop.
Earliest date available: 01/01/2019
full_time_work_prop_7dav Offers a 7-day trailing window average of thefull_time_work_prop.
Earliest date available: 01/01/2019
part_time_work_prop_7dav Offers a 7-day trailing window average of thepart_time_work_prop.
Earliest date available: 01/01/2019
median_home_dwell_time_7dav Offers a 7-day trailing window average of the median_home_dwell_time.
Earliest date available: 01/01/2019

After computing each metric on the census block group (CBG) level, we aggregate to the county-level by taking the mean over CBGs in a county to obtain the value and taking sd / sqrt(n) for the standard error, where sd is the standard deviation over the metric values and n is the number of CBGs in the county. In doing so, we make the simplifying assumption that each CBG contributes an iid observation to the county-level distribution. n also serves as the sample size. The same method is used for aggregation to states.

SafeGraph’s signals measure mobility each day, which causes strong day-of-week effects: weekends have substantially different values than weekdays. Users interested in long-term trends, rather than mobility on one specific day, may prefer the 7dav signals since averaging over the preceding 7 days removes these day-of-week effects.

### Lag

SafeGraph provides this data with a three-day lag, meaning estimates for a specific day are only available three days later. It may take up to an additional day for SafeGraph’s data to be ingested into the COVIDcast API.