During this pandemic, epidemiologists have been portrayed as clueless idiots who "got everything wrong". That makes sense only if one ignores the evidence. I can go so far as to say that epidemiologists have gotten everything right - they have not predicted every detail but they have nailed the big picture. (They told us about re-opening too soon, second waves, viruses not chased away by summer heat, etc. etc.)
Remember just a month ago, when cases started to surge in Texas in June, many people looked at the glass half full - they said deaths weren't increasing even as cases exploded. This was the picture they were looking at:
I wrote a blog about this statistical artifact at the end of June. Deaths always lag cases. I said you've got to have patience. Stop interpreting daily tracking charts, and wait a few weeks.
It's more than a month later. What does the chart look like?
By early July, deaths from Covid-19 started to rise rapidly in Texas. In fact, the slope of the growth of deaths in July is roughly the same as the slope of the growth in cases in mid-June.
To see what happened more clearly, I shift the gray line (cases) to the right by three weeks. You can see that deaths and (shifted) cases have changed in lock step.
This chart reveals a couple of insights.
First, the time lag is sufficient to explain everything. There have been speculation about other contributing factors, such as better treatments, and younger patients but those factors are not necessary to explain the trends in cases and deaths. It's important for any insights to be validated by the experience on the ground. Hospitals should know how long an average patient who eventually dies from Covid-19 stays hospitalized.
Second, notice the weird spike in deaths on July 27 (the spike has already been tamed by a 7-day moving average); that's due to a change in how deaths are counted. Here are some notes from the Covid Tracking Project about all the recent changes to how they count things in Texas:
The recent switch of requiring deaths to be confirmed by death certificates, for example, introduces a delay in reporting. It may take a week or two for a death to appear in the data. It would take quite a bit of effort to go back and switch the entire series of data to reflect this new definition. Meanwhile, it's impossible to trust the dates of deaths.
Every note listed above should concern the data analyst. That's the key reason I cannot have confidence in the 3-week time-lag estimate described above. It must come with a margin of error, probably of at least 1 week, to account for data deficiencies, known and unknown.
It's very sad to see that the Covid Tracking Project team has rated Texas's "data quality" as grade A. I can't even imagine how bad the data quality is to earn a B or C grade!
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