R_t Covid-19

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Calculating R_t

Model Updates

• The current model uses the same math as in the notebook.
• The model is evolving rapidly and while values should not change dramatically, there may be changes to historical values when we find improvements or fix data anomalies. You can download the latest run here and email us with any suggested model improvements.

Known Issues

• Connecticut saw a very large increase in cases relative to its baseline on 4/20 due to "true-up"-ing their calculations with the CDC's guidelines for which cases should be counted. Their R_t will normalize in the coming days.
• Washington State had several days from 4/10 to 4/13 without reporting new cases. They've resumed reporting and our model will continue to improve its R_t estimate for WA as more days come in.
• Absolute testing levels should not affect this algorithm much, but a fast ramp or decline in testing will affect numbers.
• There is a delay between onset of sickness and testing positive, this is not reflected in these numbers. Actual R_t values are delayed by some amount.
• While we make a best effort to accurately describe R_t, nothing can do that perfectly - please calibrate accordingly.

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