Focus testing is suitable for large scale mass testing (province, region, or country). This strategy requires 10% more test that standard mass testing, but increases the positive predictive value 30-fold (from 2,6% to 90%) in low-prevalence areas. Further, the rate of false negatives is kept at acceptable levels.
Double testing is designed for smaller high-prevalence zones (city, county, province).
Compared to standard mass testing, this strategy reduces the rate of false negatives by 50% to 65%, that is infected people who are tested negative, but comes at a cost of 107% additional tests. The combination of the two is also promising: focus testing in low prevalence zones, and double testing in high prevalence zones. An analysis by Miquel Oliu-Barton, associate professor at Paris-Dauphine University) and Bary Pradelski, associate professor at the CNRS, associate member of the Oxford-Man Institute for Terra Nova.
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