17th May 2020
Notes on the Miami-Dade serological study – IFR upto 0.31%
“Taking the fatality number for 21 days after the median testing date, the IFR is 0.17% to 0.31%. This is likely an overestimation as most people use a 14 day delay.” [Source]
The study, spurred by Miami-Dade County officials, will be an ongoing weekly survey based on antibody testing — randomly selecting county residents to volunteer pinpricks of their blood to be screened for signs of a past COVID-19 infection, whether they had tested positive for the virus in the past or not. The goal is to measure the extent of infection in the community.
Miami-Dade researchers partnered with Florida Power & Light to randomly generate phone numbers and invite people to come to 10 drive-thru testing locations. Preliminary results released on April 24, based on two weeks of testing and about 1,400 participants, estimated that about 6% of the Miami-Dade population had antibodies. [Source]
In a survey conducted in Miami, random digit dialing was used to recruit a representative sample of participants. Participants then agreed to visit a drive-thru testing site. Bias can still occur if people do not consent or do not have a car, but it’s a creative approach. [Source]
In Miami, 750 new participants are recruited each week (repeated cross-sectional studies). Longitudinal studies, where the same people are sampled every 3-plus weeks, are especially valuable, allowing us to examine antibody dynamics over time to look for waning.