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Divia Eden

@diviacaroline

Jan 5

I think I was following this thread until I got to this graph—can someone explain the blue squiggles to me please!

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Trevor Bedford

@trvrb

Jan 5

With these "phase diagram" plots, I'm attempting to show how case load is related to epidemic growth rate across states. The trajectory of Omicron is shown as a red line with per-capita case count on the x axis and epidemic growth rate on the y axis. 8/12

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The axes are the quantity of interest (cases per day per 100k) and the rate of change of that quantity (in slightly weird non-linear units). Bottom right means "many cases, slow/negative growth" and top left means "few cases, high growth".

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These "phase plots" are a pretty common way to analyze dynamical systems, especially "first-order" ones where the future depends only on the current value and the current derivative of that value.

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so concretely- a straight line in the top half of the plot is exponential growth, in the bottom half of the plot is exponential decay. a line that starts out straight and then goes down towards zero (on the y-axis) would be sigmoidal (or roughly like that)

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And a clockwise squiggle is probably the control system (broadly construe) at work: cases rise, people and institutions become more cautious, growth rate falls, cases fall, people become less cautious, growth rate rises.