@@ -15,11 +15,13 @@ grand_parent: COVIDcast Main Endpoint
1515* ** Time type:** day (see [ date format docs] ( ../covidcast_times.md ) )
1616* ** License:** [ CC BY-NC] ( ../covidcast_licensing.md#creative-commons-attribution-noncommercial )
1717
18- The COVID Act Now (CAN) data source provides COVID-19 testing statistics, such as positivity rates and total tests performed.
19- The county-level positivity rates and test totals are pulled directly from CAN.
20- While CAN provides this data potentially from multiple sources, we only use data sourced from the
18+ The [ COVID Act Now (CAN) ] ( https://covidactnow.org/ ) data source provides COVID-19 testing statistics, such as positivity rates and total tests performed.
19+ The county-level positivity rates and test totals are pulled directly from CAN using [ their API ] ( https://covidactnow.org/data-api ) .
20+ While CAN provides this data potentially from multiple sources, we only use data that CAN sources from the
2121[ CDC's COVID-19 Integrated County View] ( https://covid.cdc.gov/covid-data-tracker/#county-view ) .
2222
23+ Delphi's mirror of the CAN data was deactivated in December 2021 (last issue 2021-12-10) in favor of the [ DSEW CPR data] ( ./dsew-cpr.md ) , which reports the same information under the ` covid_naat_pct_positive_7dav ` signal.
24+
2325
2426| Signal | Description |
2527| --------------------------------| ----------------------------------------------------------------|
@@ -34,9 +36,9 @@ While CAN provides this data potentially from multiple sources, we only use data
3436
3537## Estimation
3638
37- The quantities received from CAN / CDC are the county-level positivity rate and total tests,
38- which are based on the counts of PCR specimens tested.
39- In particular, they are also already smoothed with a 7-day-average.
39+ We receive county-level positivity rate and total tests from CAN, originating from the CDC.
40+ These quantiles are based on the counts of PCR specimens tested.
41+ They are also already smoothed with a 7-day-average.
4042
4143For a fixed location $$ i $$ and time $$ t $$ , let $$ Y_{it} $$ denote the number of PCR specimens
4244tested that have a positive result. Let $$ N_{it} $$ denote the total number of PCR specimens tested.
7981
8082### Smoothing
8183
82- No additional smoothing is done to avoid double-smoothing, since the data pulled from CAN / CDC
84+ No additional smoothing is done to avoid double-smoothing, since the CAN data
8385is already smoothed with a 7-day-average.
8486
8587## Limitations
8688
87- Estimates for geographical levels beyond counties may be inaccurate due to how aggregations
88- are done on smoothed values instead of the raw values. Ideally we would aggregate raw values
89+ Estimates for geographical levels beyond counties may be inaccurate because our aggregations
90+ are performed on smoothed values instead of the raw values.
91+ Ideally we would aggregate raw values
8992then smooth, but the raw values are not accessible in this case.
9093
91- The positivity rate here should not be interpreted as the population positivity rate as
94+ The reported test positivity rate should not be interpreted as the population positivity rate as
9295the testing performed are typically not randomly sampled, especially for early data
9396with lower testing volumes.
9497
9598A few counties, most notably in California, are also not covered by this data source.
9699
97- Entries with zero total tests performed are also suppressed, even if it was actually the case that
100+ Entries with zero total tests performed are suppressed, even if it was actually the case that
98101no tests were performed for the day.
99102
100103## Lag and Backfill
101104
102105The lag for these signals varies depending on the reporting patterns of individual counties.
103106Most counties have their latest data report with a lag of 2 days, while others can take 9 days
104- or more in the case of California counties.
107+ or more, as is the case with California counties.
105108
106- These signals are also backfilled as backlogged test results could get assigned to older 7-day timeframes .
107- Most recent test positivity rates do not change substantially with backfill (having a median delta of close to 0).
108- However, most recent total tests performed is expected to increase in later data revisions (having a median increase of 7%).
109+ Revisions are sometimes made to the data. For example, backlogged test results can get assigned to past dates .
110+ The majority of recent test positivity rates do not change substantially with backfill (having a median delta of close to 0).
111+ However, the majority of recent total tests performed is expected to increase in later data revisions (having a median increase of 7%).
109112Values more than 5 days in the past are expected to remain fairly static (with total tests performed
110113having a median increase of 1% of less), as most major revisions have already occurred.
111114
112115## Source and Licensing
113116
114- County-level testing data is scraped by CAN from the
117+ County-level testing data is scraped by [ CAN] ( https://covidactnow.org/ ) from the
115118[ CDC's COVID-19 Integrated County View] ( https://covid.cdc.gov/covid-data-tracker/#county-view ) ,
116119and made available through [ CAN's API] ( https://covidactnow.org/tools ) .
120+
121+ The data is made available under a [ CC BY-NC] ( ../covidcast_licensing.md#creative-commons-attribution-noncommercial ) license.
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