Have I got this right?

[Wingedharpy]

Just asking.

Currently, it appears that Covid testing is being targeted at those most likely to test positive ie. people who have symptoms, or have been in close contact with someone who is positive, key workers etc etc

I'm currently living in a local "hotspot" for Covid and am therefore able to book a test, should I choose to, even though the chances of me testing positive are miniscule for reasons I won't bore you with.

I understand that the WHO say that for an epidemic to be considered under control, less than 5% of those tested should test positive over a 14 day period.

Is the way to take us out of the hotspot, therefore, for people like me (ie. the almost certainly negatives) to go and get tested?

If we are targeting tests toward the most likely positive folk (and I can fully appreciate why we would do that) will we ever get to the less than 5% stipulated by WHO?

Anyone?

No. its when you get to 5% positive of those who actually are indicated for testing.

@teateateateateamoretea : by "those who actually are indicated for testing", do you mean people with symptoms?

Take a scenario:
If lots of people did pretend to have symptoms, get tested and then the 5% or less is achieved. Then if that was the main criteria for you being a hotspot (there are others such as hospital numbers, number of cases), then if you then came out of hotspot classification, by fiddling this number, you’d still have the same number of cases etc. Doesn’t seem like a great idea? Why do you want to be not a hotspot if you are?

The WHO classification is irrelevant when it comes to Tiers, if that's the concern.

I think, maybe, you've misunderstood my questions, GreyishDays.

I'm not suggesting for a moment that anyone fiddles anything.

I'm just thinking, it's a bit like trying to work out how many people in the community are left handed but the only people we ask are those that are left handed and their children.

@PatriciaHolm

The WHO classification is irrelevant when it comes to Tiers, if that's the concern.

Not true in Scotland, positivity rate is used to decide the levels.

One of a few criteria, I should say.

@Wingedharpy

I think, maybe, you've misunderstood my questions, GreyishDays.

I'm not suggesting for a moment that anyone fiddles anything.

I'm just thinking, it's a bit like trying to work out how many people in the community are left handed but the only people we ask are those that are left handed and their children.

But that’s the same for every area? It’s still providing a comparison.

Lots of people will go and get a test for a cough, say. Or a temperature. If there are few cases then the % positive will be low.

Wasn't so much thinking about tiers Patricia, just percentages generally ie. how would we get to 5% if we're aiming the tests in the way we are.?
Also, are the cases per 100,000 extrapolated from the number of tests done v number of tests with positive result?

I mean people who don’t have it.

You know the % positive isn’t static?

Can you say this bit again, I’m being thick

Also, are the cases per 100,000 extrapolated from the number of tests done v number of tests with positive result?

I think what the WHO actually said was they recommended "that the percent positive remain below 5% for at least two weeks before governments consider reopening."

It's not set in stone, I don't think it's an official definition of anything that I can see.

Any determination of how we are progressing needs to take into account a number of factors, positivity just one of them, as it can (as you say) be skewed by who you are testing.

For interest, here are the factors that Scotland is using.

Greyish, I suppose I'm asking how do they calculate the number of cases per 100,000 people in a given area?
What is the formula?

You're not being thick at all, just very patient with someone who's struggling to understand !😊

Ah. So in say Leeds there are 100 cases on Tuesday, population is 500,000.

So 500,000/100,000 is 5.
So cases per 100,000 is 100/5 = 20.

So any area can be compared, regardless of actual population.

@teateateateateamoretea

No. its when you get to 5% positive of those who actually are indicated for testing.

This.

It would be irresponsible of people to start getting tested "to get out of a hotspot" because that would be skewing the results. The 5% will have been recommended for a sample of people indicated for testing.

The percentage would need to be a lot lower if they were testing everybody.

Let's say you were doing a study to look at pregnancy where women didn't know they were pregnant and were testing a random sample of women who believed they weren't pregnant. Now think about what would happen to your results if you tested a random sample of men and women.

Orangenasturtium, sorry.
I worded the OP badly.
I didn't mean we should be doing anything to manipulate the figures, but, rather, would testing more people generally, give a better idea of the "real" picture - which won't be real anyway as there will always be people who have textbook symptoms but will not get tested as they don't want to know for whatever reason.
Greyish - that makes complete sense now -thanks.

No worries Wingedharpy!

Yes, you're right, testing a large random sample would give us a better picture of the situation. However, if you did that, the percentage of positive tests would need to be a lot lower than 5% for the epidemic to be considered under control.

Interestingly, I don’t think doing mass testing in Liverpool did give any dramatic results. I didn’t pay that much attention though.

You could expect the figures to be:

Lots of cases (actual numbers and per 100k population), because of asymptomatic ones are being picked up which wouldn’t usually.

Lower % positive rate per people tested as general population was being tested (as you’ve mentioned).

I’m not aware of either of those, but didn’t pay close attention. Be interesting to see what did happen.

Oh and the ONS does do a large random sampling thing, doesn’t it?

OP you are right. The testing sample is biased as only people with symptoms or those directed to get tested by public health as potential close contacts are getting tested, hence you are going to find more cases than if you tested the general population.

They don’t direct close contacts to get tested.

I think it depends on the proportion of asymptomatic cases doesn’t it?

The testing sample is biased as only people with symptoms or those directed to get tested by public health as potential close contacts are getting tested, hence you are going to find more cases than if you tested the general population which is why the criteria of less than 5% postivie tests in a 14 day period for the epidemic to be considered under control would be different.