[FRIAM] COVID19 R(t) for each state over time.

[Steven A Smith]

This just in via Josh Thorpe.

I've been wondering if anyone had a methodology for calculating the
COVID19 R /Replication Number./

    https://rt.live/

apparently adapted from our own (LANL) Luis Bettencourt's work on H5N1
using a Bayesian approach

    https://github.com/k-sys/covid-19/blob/master/Realtime%20R0.ipynb

This notebook is pretty big and pretty dense, I'm trying to skim through
it and get a feel for it.

It appears superficially that they are using nothing more than reported
new cases smoothed by a Gaussian filter to remove reporting/test/delay
artifacts.

What I'm not clear on quite yet is how (if) this approach handles the
intrinsic delay between exposure and onset of symptoms sufficient to
yield a confirmed case?    If that (variable) delay is not factored in
then the R(t) would seem to be a smeared reflection of R(t-n...t) where
"n" is the maximum number of days between exposure and confirmation.  
I'll keep looking.

I wish the summary view had a time-slider to watch the states R(t)
evolve... the buttons included for different previous times (yesterday,
last week, 2 weeks, 3 weeks) give a hint of this.

I'm surprised at how high some of the R values were even over 4.0 for
some states at some time.

I'm also surprised at how many states seem to have dropped to/below
1.0.   And also how many seem to have dipped below 1.0 and bounced back
up.   This would seem to imply that many states hit a high level of
social distancing/hygiene and then relaxed it (recently?).

I also haven't sussed out why the different states have such different
error envelopes...

I look forward to others possibly digging into this and sharing their
observations.

- STeve

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