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research sensitivity, specificity

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Marc Bevand
2020-06-10 20:35:36 -07:00
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@@ -26,7 +26,8 @@ Ages 0 to 199: 2428102 infected, 27121 deaths, 1.117% IFR
```
The average IFR for Spain is **1.117%**. However the true IFR may be higher due
to right-censoring and under-reporting of deaths.
to right-censoring, under-reporting of deaths, or low specificity of the serological test;
or the true IFR may be lower due to low sensitivity of the serological test.
The Spanish serological study remains the largest published study available to
this day. The age-stratified IFR was calculated from three sources:
@@ -52,6 +53,24 @@ was only available for 20 585 deaths, and was missing for 6 536 deaths.
We assume that these 6 536 deaths were distributed proportionally—not equally—among age
brackets, which seems to be a reasonable assumption.
Regarding the specificity of the commercial test used (COVID-19 IgG Rapid Test
Cassette by Zhejiang Orient Gene Biotech Co Ltd) we found various claims, all
100% or close, so no significant false positives are expected:
* 100% claimed by the manufacturer ([serosurvey][sero], page 3)
* 100% measured by the Ministry of Health ([serosurvey][sero], page 3)
* 99.2% measured by a [third-party][hoffman]
However the sensitivity is more uncertain:
* 97% claimed by the manufacturer ([serosurvey][sero], page 3)
* 79% measured by the Ministry of Health ([serosurvey][sero], page 3)
* 93.1% measured by a [third-party][hoffman]
So a false negative rate anywhere from 3% to 21% could be possible, and we
think it is premature to adjust IFR calculations given the exact sensitivity is
not known.
# Applying the age-stratified IFR to other countries
The script `calc_ifr.py` is also able to apply the age-stratified IFR to
@@ -75,3 +94,4 @@ health, etc, so this estimate should be interpreted with caution.
[daily]: https://www.mscbs.gob.es/profesionales/saludPublica/ccayes/alertasActual/nCov-China/documentos/Actualizacion_120_COVID-19.pdf
[dailyalt]: https://www.mscbs.gob.es/profesionales/saludPublica/ccayes/alertasActual/nCov-China/documentos/Actualizacion_109_COVID-19.pdf
[wpop]: https://worldpopulationreview.com/countries/spain-population/
[hoffman]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7178815/