17th May 2020
Notes on the New York serological study – IFR 0.86%
IFR = 0.863%
Haven’t had time to review the numerator. If they are not including excess deaths, then the IFR could be higher.
On April 23, Cuomo announced preliminary data from the state’s sero-survey, saying that 13.9% of state residents had tested positive for antibodies. In New York City, it was about 21%. The state is continuing to test residents in order to generate an ongoing series of “snapshots” of the levels of infection. Cuomo had updated numbers by April 27 showing huge regional variation.
Kilpatrick, from UC Santa Cruz, said that if the estimates from New York stand up to scrutiny, the infection fatality rate in New York City would be approximately 0.8%. [Source]
on Thursday, New York Gov. Andrew Cuomo announced that roughly one in five people in New York City and nearly 14% statewide had antibodies. The New York estimate was based on a sampling of 3,000 grocery store shoppers. [Source]
Applying this knowledge to Thursday’s results from New York puts the picture in sharper focus. The release from the state doesn’t disclose the sensitivity of the test used, but it does note the specificity is between 93% and 100%, a “huge range,” Ashish Jha, head of Harvard’s Global Health Institute, noted on Twitter. If the test performed at the low end of that range, New York’s infection rate would be closer to 7% — half the figure Cuomo announced — and nearly one out of every two positives would have been a false positive, Jha said.
“These tests don’t perform like people think they do and so there are a lot of crazy results,” Osterholm said. “You can often find more than half of the positives you do document are actually false positives.” [Source]
In New York City, researchers tested shoppers at grocery stores and big box stores. That method is still not perfectly random: You’re only testing the subset of people who are out shopping in person. “You’re not sampling people who are too old, or high risk, who don’t want to shop for themselves,” Larremore said. “You’re also sampling predominantly from people who are old enough to go shopping, or who feel that they may have been infected and think they’re safe enough.” [Source]