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Calculate the Probability that 1 Person (or more) is Infected in Group of Size n
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Created by:Dr. Jeff Gilchrist
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Last updated:July 28, 2021
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For more details on these calculations please see:
https://www.facebook.com/jeff.gilchrist.ca/posts/10157316541495766
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For an index of my COVID-19 related articles see:
https://www.facebook.com/jeff.gilchrist.ca/posts/10156941150785766
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Read this article for the background on the math:
https://blogs.scientificamerican.com/observations/online-covid-19-dashboard-calculates-how-risky-reopenings-and-gatherings-can-be/
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Inspired by Ryan Imgrund's probabilty reports:
https://twitter.com/imgrund
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For more daily COVID-19 related statistics and graphs:
http://gilchrist.ca/jeff/COVID-19/
http://gilchrist.ca/jeff/COVID-19/vaccine.html
http://gilchrist.ca/jeff/COVID-19/Ottawa.html
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Formula:
Where p is the per-person probability of being infected, and n is the size of the group
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Ottawa, ON, Canada
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# Active COVID-19 Cases (Ottawa):42Get latest from:
https://www.ottawapublichealth.ca/en/reports-research-and-statistics/daily-covid19-dashboard.aspx
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Population (Ottawa):1006210See:
https://ottawa.ca/en/city-hall/get-know-your-city/statistics-and-economic-profile/statistics/current-population-and-household-estimates
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Population (Ontario):14745040Q2 2020 See:
https://www150.statcan.gc.ca/t1/tbl1/en/tv.action?pid=1710000901
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Seroprevalence (Ontario):1.2%October 31, 2020 data:
https://www.publichealthontario.ca/en/data-and-analysis/infectious-disease/covid-19-data-surveillance/covid-19-serosurveillance
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Ottawa Cases on October 31, 2020:7000See:
https://open.ottawa.ca/datasets/covid-19-cases-and-deaths-in-ottawa
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Ontario Cases on October 31, 2020:75730See:
https://data.ontario.ca/dataset/status-of-covid-19-cases-in-ontario
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Seroprevalence Factor (Ontario):2.33646480919
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Per-person probability (p):0.00004174079
Lower Bound: only known active cases from positive tests, best case scenario, doesn't account for those infected who never got tested
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Seroprevalence (Ontario factor) per-person prob. (p):0.00009752589
Seroprevalence (Ontario factor): active cases + factor for 1.2% prevalence of COVID-19 in Ontario via antibody blood tests, best estimate for real # of infections in a city
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Group Size (n)
Lower Bound (Active Cases)
Active + Seroprevalence (1.2%)
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100.0%0.1%
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150.1%0.1%
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250.1%0.2%
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500.2%0.5%
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1000.4%1.0%
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2501.0%2.4%
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5002.1%4.8%
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10004.1%9.3%
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20008.0%17.7%
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500018.8%38.6%
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Note: Feel free to make a copy of this spreadsheet and change the # active cases, population, seroprevalence, and group sizes for your area and calculate what you are interested in knowing.
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You can do this by selecting "File -> Make a copy" within Google Sheets which will let you edit the values.
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