On Thursday, February 3, American Experiment reported on a new study by economists at Johns Hopkins University that finds the body of empirical evidence shows lockdowns had “little to no effect on COVID-19 mortality.” That’s obviously a big deal and a big story. It runs directly counter to the...
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A solid methodology
The study rests on a solid methodology that follows a traditional meta-analysis framework. It begins with a systematic search that identified 18,590 studies and then screened those studies based on the strength of how the study established a relationship between lockdowns and mortality.
The “difference-in-difference” criteria they use focuses on studies that measure the difference in how mortality changed after the fact compared to a control group (i.e., a geographical region that did not lockdown in the same way). This offers the best measure of what actually happened. Thus, they excluded studies that involved before-and-after comparisons, simulations, and counterfactuals based on modeled forecasts. Ultimately, this process winnowed the number of studies that qualified to be included in the meta-analysis to 24.
Each of the studies was then separated into three groups. The first group assessed effectiveness based on a lockdown stringency index of Oxford University that measures the strength of the lockdown across nine parameters, such as closing schools, stay at home requirements, and travel bans. The second group included studies on the effectiveness of shelter-in place orders and the third included studies of specific orders.
When evaluating the studies, the authors considered 4 quality dimensions. First, peer-reviewed studies were considered higher quality than working papers. Second, studies assessing longer periods that ended after May 31, 2020 were considered higher quality because they covered the first wave more fully. Third, because about 3 weeks passes between infection and death, studies that identified an early effect on mortality sooner than 14 days after the lockdown policies began were considered lower quality. Fourth, social science studies were considered higher quality than natural science studies because socialist scientists have more expertise in evaluating policy interventions.
Results show little to no effect on mortality"
It's the science.