Can someone explain to me in layman's terms?

[fustratedflo]

Can someone please explain to me in layman's terms what the R value is. I'm sure it's not that complicated but I struggle to follow when they talk about it on the news. I read that the R value has gone up today, what does this mean? Is this bad news? Is it true? Should I be even more worried than I am now? Because I'm already petrified of this virus!

The R value is the number of people that an infected person is likely to infect.

So if I had the virus statistically I’d infect x amount of people

Have you watched the government cartoon of it?

The reason it's important because if I infect x people and each of them infects x people, that's x squared people... then if they all infect x people that's x cubed.

So if R is 2 it's 2, 4, 8, 16, 32 ... exponential growth. Over a thousand after 10 'steps'

But if out every two people who have it, only one infects one other person the. r is 0.5 then the progression is 0.5, 0.25, 0.0625, .... it gradually peters out.

I don't know what R actually stands for but I think of it as Reproduce.

If the R number is 1 it means that people who already have it will infect 1 other person each (statistically speaking). Before lockdown it was around 3, so for every 1 person infected, they would spread it to 3 other people, which is why the number of infected people increased so much.

It can be confusing when the number is below 1 - how can you infect 0.7 of a person? It can be helpful to multiple by 10 or 100 and think of it in whole numbers. Eg if the R number is 0.7 that would mean for every 10 people infected, they would spread it to 7 people in total. Therefore numbers of infected people would gradually decline.

Thank you Errol that is brilliant - I already understand what R means but I could never understand how multiplying two numbers together could make a smaller number but that illustrates it perfectly. And I'm ashamed to say I was considered quite good at maths at school.

Just play with different values using a calculator, just keep multiplying a number by itself for say 5 or 10 steps. (I've just realised i missed 0.125 when writing out the series of multiplying 0.5 )
Or use the exponential function (x superscript y )

Read this, OP. I love this graphic.

if you multiply by a number larger than one, the result will always be higher, it you multiply by a number smaller than one, the result will be lower.

The R number is how quickly the virus can be spread, the higher the number the more people can get infected

This might help...
www.bbc.co.uk/news/av/health-52494495/coronavirus-r0-what-is-the-r-number-and-why-does-it-matter

labblog.uofmhealth.org/rounds/how-scientists-quantify-intensity-of-an-outbreak-like-covid-19

Surely it's just a statistical chance though? I don't understand why they keep saying R will go down as the weeks go on when they're opening more places up

How is the government (or whoever is publishing the data) work it out?

We don't know how many people actually have it. Some people have it but don't show symptoms. Different people take different times to show symptoms.

Surely, there must be a lag between the current data and actual R value.

"Surely, there must be a lag between the current data and actual R value"

Yes, 2-3 weeks, based on incubation period of 5-6 days (range 2-14) and then typically 6 days until hospitalisation needed. Though that 6 days might shorten a bit when widespread community testing is readily available.

The R0 isn't fixed, but is based on

• how long someone with the disease remains infectious
• how likely it is they would infect those they were in contact with
• how many people they are in contact with

The first two points are characteristics of the virus.

The third is about people, and is the one we can change, and is the point of locking down

It's perhaps worth adding a fourth criterion separately (it affects the second and third points) which is whether the virus is transmitted by people who don't have symptoms (either for the first few days or ever)

As soon as we realised that, unlike the previous SARS, there could be asymptomatic transmitters/carriers it was clear this was much more likely to become a pandemic.

The likelihood of infecting people you are in contact with can also be hopefully controlled in the future. For example measles is very contagious (much more so than covid) but it doesn't spread because we are mostly vaccinated. Most adults are immune to chickenpox because they had it as a child, and catching chickenpox confers lifelong immunity (we don't know whether this is true for covid). Flu is partially controlled for vulnerable people by a yearly jab.

Sorry for the late response but thank you so much to everyone. It definitely makes more sense now