Before I
discuss this, the attached image contains the overall spreadsheet and most assumptions
are detailed on the page. I don’t
declare any infallibility (papal or otherwise), but if you think I’ve made a
mistake contact me and I’ll upload a corrected version (if required).
I’m not
drawing any specific conclusions on what our behaviour should now be, I
did this to consider my own risk level for venturing out so that I could do so
on a more scientific basis rather than gut reaction.
I used the
following assumptions/default values:
- The
infection rate is 1 person in 3,900 (the last one i saw)
- You need
face to face exposure of 15 minutes to risk transmission of the infection
- Whilst the
face covering mitigation %'s that have been circulating for some time are not
proven, I have used heavily moderated values to explore the impact of face
coverings
- I've ignored
the risks (and maths) of meeting more than 1 carrier of C-19 in any one day
- I have
ignored the fact that infection is not evenly distributed around the country,
these numbers do not apply to hot spots.
- Equally,
these numbers overestimate the risk in cold spots (if that is the opposite of
hot spot!)
- This does
not consider behaviour patterns whilst out – if you go to the pub and hug all
your mates, then your risk likely increases – the behaviour assumed is that social distancing is observed.
- This ignores
whether the exposure is indoors or outdoors
- The
percentages shown don’t actually demonstrate the chance that you will get a C-19 infection,
they show the risk of you participating in a face to face meeting where the
risk of transmission can occur. So given
transmission is not certain, this means the risk % overstate the chance of you
(on average) catching C-19 from that contact.
- Finally,
even if the event does transmit C-19 to you, it says nothing about the risks of
you falling ill (seriously or not) with C-19
The
calculation in the second column is done from this logic:
- The risk of
someone being infected is 1/3900 – call this X. In percentage terms this is 0.00000256410256
- The chance
of any 1 person you meet being infection free is (1- X) which is
0.99999743589744 or 99. 999743589744%, call this Y
- The chance
of all the people you meet being infection free is therefore the value in Y multiplied
by itself once for each person, so for 10 people all to be infection free is Y*Y*Y*Y*Y*Y*Y*Y*Y*Y
or Y^10. Which is roughly 99.744%.
- Which means
the probability of 1 or more people you meet being infect is 100%-99.744% which
is my calculated 0.26%.
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| Image from calculation spreadsheet |
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