COVID-19 May 01, 2020

And so another month begins.  Where will the month end?  Unlike April, where the trajectory was mostly predictable, May is likely to be much more uncertain.  New daily cases are not falling.  They have more or less leveled off with a very, very large weekly oscillation superimposed.  On the other hand, the death rate is falling, slowly, on average but also with a large weekly oscillation. 

For now, the infections and deaths are inconsistent unless the mortality rate is changing substantially over time. If the mortality rate is invariant, then deaths should track infections with a lag.  Will deaths start to level off over the next week?  If not, that suggests that the behavior of the infection data is due to changes in testing and reporting.  It means that that data becomes almost useless without substantial analysis to remove the spurious signal.  It means that, for now, the death rate will be one of the few easily accessible and analyzable data for tracking this pandemic. 

COVID-19 April 30, 2020

As each day passes, the meaningfulness of infection numbers seems to diminish.  The number of tests continues to ramp up and this strongly affects the statistics.  The more tests you conduct on symptomatic people or people that have likely been exposed to the virus, the greater number of positives you'd expect.  Is this why the number of new cases confirmed each day leveled off?  It may be possible to answer this question at some time in the future when a clever epidemiologist is able to sift through the chaos that is the states' testing programs, but I don't think it's possible to do this in real time anymore.  That's a real problem because the number of new cases each day should be an important metric for determining the effectiveness or consequence of policy.

There are other metrics.  The number of daily deaths remains an important number.  I've said the dead are almost always counted.  The use of "almost" is appropriate.  Some dead are not counted.  Or, rather, some dead are counted but not attributed to COVID.  Sometimes they are counted long after they've died.  And, based on the unconfirmed news coming out of Florida, sometimes the dead are intentionally miscounted.  Perhaps this metric will soon become as unreliable as the number of new cases.  After that, we may have little left but to monitor hospital load.

Below are today's graphs.  The number of new daily cases is not decreasing as would be expected.  That has caused the cumulative number of cases to continue to rise at a greater rate than would be expected.  It is not quite an exponential rise, but rather a near linear increase with time. Total deaths and daily deaths are still well behaved with respect to the model.

COVID-19 April 29, 2020

Just a short post today with the graphs.  Daily new cases have settled down a bit, but the trend over the last week still does not match with the prior trends.  Testing is really ramping up in many states and social distancing policies are in flux.  All of these can lead to a departure from the prior trend.  We'll just have to keep an eye on it.

Deaths continue to match with the model predictions.  If the behavior of infection rates is indeed changing, then that should start to show up in the death statistics.

COVID-19 April 28, 2020

After reaching the highest number of new infections just a few days ago, numbers have plummeted to the lowest they've been in nearly a month.  Yesterday's 22,000 new cases are just a little over where the model predicts they should be. The data variability makes no sense in terms of a natural system.  The behavior has to be due to some combination of reporting cycles over the period of a week combined with an overall increase in testing ability.  Superimposed on that is almost certainly a signal due to changes in the policies of individual states.  Depending on which data set you believe, we are about to cross or have just crossed 1,000,000 recorded cases.  This is an artificial number and the number of actual infections is almost certainly 10 or 20 times greater.

Daily deaths have also dipped to lows that have not been seen since early in the month.  The last two days have been substantially below the model trend, but I expect the numbers to rise, as they typically do through the weekdays.  Deaths should not be strongly tied to testing availability, but the data still suffers from reporting inconsistencies.  We have crossed the 50,000 dead mark.

COVID-19 April 27, 2020

The number of new cases dropped significantly yesterday.  This is usually the case for the weekend, which has historically been the low point of the weekly oscillation cycle.  The question for the coming week is whether the numbers will begin to take off again or whether the numbers will relax back to the model trend.  If the numbers increase again, it will be interesting to see whether they do so exponentially, which is shown by the orange curve I've added back since yesterday.  Perhaps we are starting to see the rise of the foolish states.

The number of daily deaths plummeted yesterday to one of the lowest values in weeks.  This is following the high point roughly a week ago.  If the weekly oscillation is still operating, the numbers should increase over the next few days.  The question for deaths is whether they will rise back towards the model trend.

What is interesting is that while daily new infections are climbing daily deaths are dropping.  The rise in new infections could be consistent with the increase in testing.  The number of deaths is independent of testing.  If deaths don't rise within the next week or so, that means that any continued rise in the number of infections is mostly the result of increased testing and not an actual surge in the pandemic. 

Overall, the quality of the data has become increasingly poor. The amplitude of the weekly oscillation has grown, the reporting criteria have changed from state to state, and the way that earlier cases just now discovered are added to the pile contaminates the data.  If the data collection and documentation protocol were rated by scientific standards it would be a fail minus.  It really just goes to show how poor (absent) the coordination and standards are at the federal level. 

COVID-19 April 26, 2020

Daily new cases reported on Friday departed substantially from the trend.  Yesterday's numbers are lower, but still substantially different.  I am inclined to think that a good amount of that is due to states adjusting their numbers and an increase in testing.  This is just a hunch, but as an example, the number of tests given each day in Colorado is shown below.  In the last two days, the numbers have increased by more than 2.5 times the average.  Not surprisingly then, the number of positives have increased proportionally.   I can't say whether this is true for other states, but the numbers of many other states do look suspicious.

At the same time, I do think that some states are about to undergo an increase in the rate of infections.  In principle, this increase will be balanced by a decrease in other states that have peaked.  In principle.  If too many states take their foot off the break too quickly, then it is almost inevitable there will be an acceleration of cases again.

The best metric continues to be the number of deaths.  Even these numbers, however, can be subject to uncertainty as states go back and reevaluate the cause of some deaths.  It would be acceptable if historic deaths were logged in on the day they occurred, but many states lump them into the daily statistics.  As long as those numbers aren't too great, it's not a big problem. But if New York goes back and decides that there were 8,000 additional deaths that should be attributed to COVID, and if they lump them all into next Tuesday's numbers, that's clearly going to cause problems.

Below are the graphs for today.  I've readded the exponential best fit line on the cumulative cases.  I want to see if the data begins to take off on an exponential trajectory again.  That would be bad.

COVID-19 April 25, 2020

The data reported yesterday are...interesting.....

Death statistics, both the daily deaths and the cumulative, were as expected.  The new daily infection cases, however, broke the model.  They were far higher than expected, even considering the known, weekly data oscillations.  Over 36,000 new cases were reported.  That's the largest number since...ever!  The next highest daily infection was 33,578 on April 10.  Prior to yesterday, all the data and the model indicated that we had passed the peak infection on or about April 9.  You can see the effect of this large daily increase in the cumulative data where the last point jumps above the best fit model curve.

There are really only two choices here.  Either the data has some problems and inconsistencies or the infections in the US have started down a more troubling trajectory.  The first choice is possible. There has been quite a bit of chatter about states adjusting their statistics: counting cases that had previously been unknown.  Also, testing is ramping up, so maybe the sudden increase is just a reflection of that increased testing.  The second choice is also possible.  As states relax restrictions, the number of daily infections would be expected to increase.

It may be possible to disambiguate the possibilities with time.  If it's simply a matter of a data adjustment and an increase in testing, then we might expect to see the data jump up for the next few days (or even over a week given the oscillation issue).  After that, the slope of the curves should then return to where they were.  That is, there will be a discontinuity and offset between the historical data and the new data, but the curves will be roughly parallel to each other.

If the behavior is due to a real increase in infections, then the curve will continue to steepen, and we may be able to identify the states that are most responsible.  Remember that NY/NJ account for a disproportionate number of daily cases and cumulative cases.  As those two states settle down, other states are rising and coming to dominate the statistics more strongly. Perhaps the most telling signature will be if the number of deaths begins to rise.  Death statistics lag infections.  If infections really are increasing dramatically, deaths should follow within a week or so.