This data indicates that the doubling time has been ~4 days for the past week or so. I suspect that the doubling time was faster in the beginning because testing was being rapidly ramped up and that the actual doubling time is closer to 4-5 days.
The doubling time of 4 days is based on all non-China cases combined. In the last week+ this is dominated by S Korea, Iran and Italy (75% of cases currently). All of these are later into their outbreaks where the doubling time has increased so that data does match what I’ve got (which isn’t surprising as I’m using the same data).
The hypothesis that this is more to do with testing rates has a couple of problems:
The pattern is consistent across countries, not all of which had the same testing regimens or supply.
In China the death rate starts off with a doubling time of around 2-3. See appendix 2. A quick check of Italy and Iran’s death rates suggests the same thing.
Hadn’t realized that the last week was dominated by those countries, although it seems obvious in retrospect.
I think that testing being ramped up in different rates at different countries is a little incompatible with all countries exhibiting relatively the same doubling time. Countries that ramped up testing quicker should see faster doubling times, so the observed doubling time should be tied to the speed at which countries ramped up testing.
My (rough) model was that all countries basically ramped up testing at the same-ish rate once they had a non-trivial number of infections in their country, so they had fast doubling times in the beginning but slow doubling times once they had caught the majority of people infected (i.e. the infection had been spreading for many days before they realized and had to spend the first week or so of testing just trying to catch the people that were already infected). This doesn’t quite make that much sense though, because it’s obvious that not all countries are ramping up testing at the same speed. But that confuses me, because that means that the doubling time should be different for all the countries?
Thanks for this analysis. I have moderately updated towards a lower doubling time.
I’m skeptical of the 2-3 day doubling time claim.
This data indicates that the doubling time has been ~4 days for the past week or so. I suspect that the doubling time was faster in the beginning because testing was being rapidly ramped up and that the actual doubling time is closer to 4-5 days.
The doubling time of 4 days is based on all non-China cases combined. In the last week+ this is dominated by S Korea, Iran and Italy (75% of cases currently). All of these are later into their outbreaks where the doubling time has increased so that data does match what I’ve got (which isn’t surprising as I’m using the same data).
The hypothesis that this is more to do with testing rates has a couple of problems:
The pattern is consistent across countries, not all of which had the same testing regimens or supply.
In China the death rate starts off with a doubling time of around 2-3. See appendix 2. A quick check of Italy and Iran’s death rates suggests the same thing.
Hadn’t realized that the last week was dominated by those countries, although it seems obvious in retrospect.
I think that testing being ramped up in different rates at different countries is a little incompatible with all countries exhibiting relatively the same doubling time. Countries that ramped up testing quicker should see faster doubling times, so the observed doubling time should be tied to the speed at which countries ramped up testing.
My (rough) model was that all countries basically ramped up testing at the same-ish rate once they had a non-trivial number of infections in their country, so they had fast doubling times in the beginning but slow doubling times once they had caught the majority of people infected (i.e. the infection had been spreading for many days before they realized and had to spend the first week or so of testing just trying to catch the people that were already infected). This doesn’t quite make that much sense though, because it’s obvious that not all countries are ramping up testing at the same speed. But that confuses me, because that means that the doubling time should be different for all the countries?
Thanks for this analysis. I have moderately updated towards a lower doubling time.