The Growth-Severity Confound

Someone who tweets under the handle @enn_nafnlaus cautioned that it is easy to make a mistake when comparing trajectories with different exponential growth rates.

In fact, this mistake can bias down the measure of severity that is raising hopes that an omicron infection will be less serious. The bias can be large, off by something closer to a factor of 10 than a factor of 2.

The underlying problem is that fast growth dramatically increases the ratio of any quantity that we measure today compared to its value only a few days ago.

~4 minutes

Recent Timeline for the Doing Business Scandal

What follows is a timeline of events leading up to the World Bank’s decision to stop publishing the Doing Business report because of manipulation of the data used in the 2018 and 2020 reports. The timeline relies primarily on the report by the WilmerHale law firm, which is available here. I encourage anyone who wants to express an opinion about the actions of Kristalina Georgieva to read the WilmerHale report first. Failing that, and at a bare minimum, they should at least read this summary of its findings.

I was responsible for the 2017 report but was not involved in any of the events that make up this timeline. They do show that I was right to express deep concern about the ease with which country rankings could be manipulated and the likelihood that this type of manipulation could be undertaken inside the World Bank, but I will not elaborate here on my findings from the 2017 and earlier reports. Justin Sandefur has a helpful post that goes into the some of the specifics.

~6 minutes

Political Overreach, Diminished Credibility

When I was asked back in June of 2021 about lessons for science from the pandemic, the gist of what I said was:

In a democracy, the community of science can be a uniquely valuable source of objective facts, but assertions by scientists will be trusted only if they are careful not to overreach by advocating on behalf of their preferred political outcomes.

(See below for my detailed response.) Three months later, in the wake of a debate about booster shots, we can see the risk associated with overreach. In the United States, no one making decisions about boosters is paying any attention to what the people who claim to be the scientific authorities are saying.

~6 minutes

Dice, Walls and Boosters

Two opposing interpretations of the evidence about waning vaccine protection are grounded in two very different models of the course of a Covid-19 infection. In two masterful tweets, John Burn-Murdoch captured and named them: the dice model and the two-walls model.

Under the dice model, waning protection against infection implies waning protection against severe disease. Because there are fewer instances of more serious outcomes, it is more difficult to tease out statistically significant evidence of waning against a more serious outcome than against infection. But if the dice model is right, the two always go together.

Under the two-walls model, it would be possible to have waning protection for infections without waning protection for severe disease, but there is a problem with this model. Part of the beauty of the stripped-down characterization by Burn-Murdoch is that it is precise enough to surface its intrinsic logical contradiction. There is a way to patch the model to remove this contradiction, but what remains is a biologically implausible model that is starkly inconsistent with the data.

As a result, the the default presumption should be that statistically significant evidence of waning against infection also implies waning against more serious outcomes. This presumption could be overturned by tight estimates that show no waning of protection against these more serious outcomes, but not by low-powered tests that generate big uncertainty intervals.

~7 minutes

Infrequent Events and Proxy Indicators

Data from a study of vaccine effectiveness by the Mayo Clinic shows why severe disease is hard to measure accurately. In such cases, it is better to track a proxy indicator -- a canary in the coal mine -- than the indicator of interest. Vaccine effectiveness against infection is the obvious proxy indicator for effectiveness against all outcomes, which should all vary with the number of infections. Measures of effectiveness of the existing vaccines against infection show unambiguously that the protection provided by the existing vaccines is substantially lower now than it was before the delta variant took over.

~3 minutes