I was wondering about the use of the Current Population Survey to determine Labor Force Participation rates and ability to Telework during COVID broken down by each of the nine counties in the Bay Area. Is county level analysis reliable using CPS data for the Bay Area counties?
First you should check to see if these counties are all identified in the CPS data, by referring to this page. For those that are, the CPS sample was not designed to produce reliable monthly statistics at levels below state. You can read more about the sampling design in the CPS technical documentation. However, you can determine the reliability of any specific estimate by calculating confidence intervals. Also, combining data from multiple months of data will increase the precision of your estimates.
Depending on your needs, you may also be interested in using the ACS data from IPUMS USA. That data has larger samples and more geographic detail than the CPS. You can also see summary statistics for low levels of geography from IPUMS NHGIS. Topics available from NHGIS include journey to work (which can be used to infer working from home), and employment status.
Thank you for your insights Matthew!