Switch to USAFacts to avoid JHU case rate error

The error is currently being corrected, but easiest to switch to
USAFacts while we wait.

Author: capnrefsmmat

content/post/2020-10-06-survey-wave-4.Rmd

@@ -157,7 +157,7 @@ library(ggrepel)
 library(dplyr)
 library(plotly)
 
-case_rates <- covidcast_signal("jhu-csse", "confirmed_7dav_incidence_prop",
+case_rates <- covidcast_signal("usa-facts", "confirmed_7dav_incidence_prop",
                                start_day = end_day, end_day = end_day,
                                geo_type = "state")
 
@@ -384,6 +384,12 @@ reopening.
 details, see [our surveys page](https://covidcast.cmu.edu/surveys.html). For
 updates, you can follow [CmuDelphi on Twitter](https://twitter.com/cmudelphi).*
 
+**Note.** *This post was updated on October 17, 2020 to correct an error in the
+scatterplot of mask usage and reported case rates. An error in our data
+processing system meant our reported case rates were half the size they should
+have been. This did not affect the trend in the scatterplot, only the scale of
+the X axis.*
+
 **Acknowledgments.** *Many items in Wave 4 of our survey are based on work by
 the team at the Joint Program in Survey Methodology at the University of
 Maryland led by Frauke Kreuter; Adrianne Bradford and Samantha Chiu helped