In fact, the model does a very good job

Wednesday, March 25th, 2020

Peter Turchin presents a variant of a standard epidemiological model, known as SIRD (so named for the first letters of the variables it tracks: the numbers of Susceptible, Infected, Recovered, and Dead), applied to South Korea’s Covid-19 epidemic:

We want to make sure that the model does a good job approximating a variety of different angles from which an epidemic can be viewed. The next series of charts show whether the model succeeds in this. Points are the actual data, while curves depict model predictions.

Turchin Covid Models for South Korea

In fact, the model does a very good job. This increases our confidence that it has captured the essential mechanisms driving the epidemic. And we only need to add two additional features to the basic SIRD model to do this.

The key parameter in the model is the transmission rate, which determines how fast the disease spreads from the infected population to that of susceptibles. The second important parameter is the detection rate. Both of these parameters changed during the epidemic. As is well known, once the South Korean officials realized that they have an epidemic to deal with, they massively expanded their testing program and imposed vigorous quarantine measures. These measures should have increased the detection rate and decreased the transmission rate. Building these changes into the model, we can estimate when and how much these two rates changed.


  1. Anomaly UK says:

    But the most interesting aspect of the model for the longer term is the decline in Susceptibles, and that wasn’t tested in South Korea, where the vast majority of the population are still, as far as we know, susceptible.

  2. Wang Wei Lin says:

    An interesting component of the nCov pandemic is getting overlooked. Herd immunity. The quarantines may prevent enough infections and recoveries to block vectors on the next flare up.

  3. Borepatch says:

    All models are wrong. I’d like to see a 90 day projection and then see how the predictions hold up. I suspect poorly.

  4. Kirk says:

    The biggest problem we have is a lack of thoughtful preparation for all this. Obama did not refill the stocks on masks, Cuomo chose to blow money on a solar boondoggle rather than purchase the 15,000 ventilators he was recommended to buy, and on and on and on.

    Root issue is that prudent prior planning and developing a mindful awareness of what this whole globalization thing really implies did not happen. You cannot have a situation where the disease reservoirs in Southern China and tropical Africa are a few hours away from the rest of the world via airliner. At a minimum, you have to have distance and time between the new disease and “green fields” of the uninfected around the world. We never should have allowed a situation to where the Chinese Communists managed our information about the disease while simultaneously allowing those crooked bastards unfettered global access. And, it’s not like we didn’t have ample prior warning or example in SARS and the other outbreaks we’ve had. How many pandemics have come out of China because of their predilection for eating anything that moves? Even the friggin’ Black Plague probably came from some lunatic eating marmot along the Silk Road, and look what happened with that.

    Frankly, at this point? I think putting China and the mainland Chinese on a permanent quarantine list would be justified. We’ve had how many major epidemics sourced out of China in the last century-plus, starting with the 1918 Influenza epidemic that got blamed on the Spanish because they were the only ones not censoring? I think that the only one that’s not of Chinese origin was the H1N1 epidemic, and I’m not so sure about that one, either…

  5. Graham says:

    Respiratory diseases seem to come disproportionately from the South China ecosystem, going way back. I had thought that was true of H1N1 too but would have to look it up.

    The Plague could have- I recall reading the 1340s version entered the Eurosphere when Tatar besiegers sent corpses over the wall of one of the Genoese ports in Crimea, and off to the races. But I don’t know whether it was already also in the Levant, from whence it would have also had routes to Europe, or whether it went to the Levant later through Europe. Plus, it had been in Europe before with the Plague of Justinian, and not sure where that was from. Probably also via Persia from the East.

    I only just learned that measles transitioned from animal rinderpest to a human disease only during the Middle Ages, though I don’t recall where. That’s shockingly recent for a new disease form.

    Smallpox and some others, of course, probably in the earliest agricultural societies of the Mideast, since before recorded time.

  6. Graham says:

    There seem to be differing views, still, on Spanish Flu.

    I had always assumed the Kansas theory, which is still on the table. The trenches of France are another. The third possible origin, argued strongly in the late 2000s and widely considered plausible is…. China.

  7. Adar says:

    I have often wondered to what extent the constant wearing of gas masks during the Great War contributed to viral illnesses such as the Swine Flu.

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