Often, it\u00a0seems to take a while for that info to get out into everyday knowledge. (Plus, in the UK, the government keeps saying different things.) I\u00a0thought I’d try to bridge the information gap, and do some plain-English explanations.<\/p>\n
Today’s theme is numbers and measurements – e.g. deaths, cases, testing. I’ll\u00a0talk partly about the actual numbers, and partly about how we try to find them out, and the things we don’t know yet. And\u00a0then I’ve got this to refer back to if I write other things which draw on those numbers.<\/p>\n
It\u00a0got long, so I don’t necessarily suggest you read it all:<\/p>\n
- \n
- Just want a quick overview<\/strong>? See the key points<\/a> section.<\/li>\n
- More explanation<\/strong>? Don’t like statistics but do want to understand? Jump\u00a0from a key point to the particular topic you’re interested in, or browse through.<\/li>\n
- Don’t trust it until you’ve checked the sources<\/strong>? (wise!) Footnotes give more details of how I got to these conclusions.<\/li>\n<\/ul>\n<\/div>\n
(Content note for the rest of it: plain talk about death. Feel free to come back another day if you’re not in the mood.)<\/p>\n
![\"Covid-19](\"https:\/\/www.uncharted-worlds.org\/blog\/wp-content\/uploads\/2020\/07\/CovidNumbersStepByStep.jpg\")
<\/a><\/p>\n<\/a> Key points covered<\/h2>\n
\n- \n
- The\u00a0measurements<\/strong> of deaths and known infections don’t tell us<\/strong> what infections are happening right now today<\/strong>. All the measurements have a bit of a time-lag<\/a>.<\/li>\n
- So far this year – mostly during April and May – about 67 to 69 thousand people in the UK<\/strong> have died<\/a> that we wouldn’t normally expect at that time of year. This is called the “Excess deaths<\/a>“.<\/li>\n
- About 45\u00a0thousand<\/strong> of those were of people who’d tested positive for covid, who are counted in the official numbers from the Department of Health and Social Care (DHSC).(There’s also a separate count by the Office of National Statistics, based on death certificates; I’ll get into the differences<\/a>.)<\/li>\n
- “Excess deaths<\/strong>” doesn’t measure exactly the same thing<\/a> as “official number of deaths from covid”. But\u00a0it can be more useful<\/a> for comparing, because it doesn’t depend on side questions, such as how many people got tested, or what exactly you count as “a\u00a0death from covid”<\/a>.<\/li>\n
- You can’t automatically assume<\/em> that the unexpected deaths were all covid. But\u00a0for other reasons, we can deduce<\/a> that these ones probably mostly were. So\u00a0back in the spring, there were probably<\/a> about 20\u00a0thousand deaths<\/strong> in the UK which didn’t get written down as covid, but actually were<\/strong>. The\u00a0official covid deaths from the DHSC at the moment won’t include this other 20\u00a0thousand.<\/li>\n
- The\u00a0official figure for the total number of cases<\/strong> (about 294\u00a0thousand<\/strong> so far, at 19\u00a0July) should really be thought of as<\/a> “cases that we know about<\/strong>“. There are (and were) probably still a lot of infections that we don’t<\/em> know about.<\/li>\n
- The\u00a0COVID-19 Symptom Study<\/strong> is a good source of estimates<\/a> for how many UK people in the 20 to 69 age range currently have covid symptoms. That estimate<\/a> is currently being updated every day. (It\u00a0doesn’t include care homes, or people outside those age ranges, or people who have the virus without symptoms.)<\/li>\n
- There have been attempts to work out how many people have had the virus so far<\/strong>. We don’t yet have a good way to find that out<\/a>; I’ll\u00a0talk about some guesses.<\/li>\n
- Related to that question, it’s important not to assume that having the virus once gives you immunity forever<\/strong>. We\u00a0don’t know yet whether that’s the case; it’s probably more likely that immunity wears off over time.<\/li>\n
- If two areas are doing equally well at protecting people from the virus, one might still have more deaths than the other, simply because more people live<\/em> there. So\u00a0sometimes, instead of comparing the total for the whole country, it\u00a0can make more sense to compare same-size chunks<\/a>. Typically, you’d look at how many people died unexpectedly out of each million people in the area. This\u00a0would be called “excess deaths per million people<\/strong>“.<\/li>\n
- Based on all the numbers discussed here<\/a>, it looks as though in the year so far, up to 19\u00a0July, the UK has had something in the region of 800\u00a0to\u00a01,000 excess deaths out of every million<\/strong> people in the country. So\u00a0far, this is similar to Spain<\/strong>, a\u00a0little bit worse than Italy, about twice as bad as France, and much<\/em> worse than Germany, Greece or Denmark.<\/li>\n
- Of every 200<\/strong> people who gets infected with covid, at the moment it looks as though typically 1\u00a0or 2<\/strong> would die. The\u00a0exact number isn’t known yet<\/a>. However, that doesn’t mean that any random person has the same risk; for example, older people are more likely to die of it than younger people.<\/li>\n
- We don’t know yet<\/a> how many previously-healthy people will remain long-term disabled<\/strong> as a result of a covid illness, such as a stroke, damaged lungs, or post-viral fatigue.<\/li>\n
- Because the illness is very new, death risks and disability risks are both likely to improve<\/a> over the months, as doctors & researchers learn more<\/strong> about the best treatments<\/strong>.<\/li>\n
- The\u00a0“R” number<\/strong> is way of summing up roughly how successfully the virus is managing to spread around. It’s\u00a0how many other people would typically be infected by 1\u00a0infected person<\/a>. For\u00a0a particular virus, it\u00a0changes over time<\/a>, depending on what’s going on with the humans.<\/li>\n
- Another way to talk about the epidemic growing or shrinking is the “growth rate<\/strong>“. For example, if\u00a01,000 people caught the virus yesterday, and 1020 people catch it newly today, that would be a “growth rate<\/a>” of 2% (two per cent). Or\u00a0if 980 people catch it newly today, that would be a “growth rate” of -2% (minus<\/em> two per\u00a0cent).<\/li>\n
- At the moment, the UK<\/strong>‘s epidemic is probably about holding steady<\/a>, with deaths around 100 a day, mostly in England. Scotland is doing better than England; they’re down to about 1\u00a0death a week at the moment.<\/li>\n
- “Pillars 1 & 2” of the English government’s testing<\/strong> plan both relate to “who’s got the virus now<\/strong>” type testing, where you want the answer back as quick as possible. Pillar 1 is via labs in the National Health Service and Public Health England. Pillar 2 is the privatised services, e.g. drive-in testing.Some useful measurements to track would be:\n
\n- \n
- How quickly<\/strong> can people get a test<\/strong> if they want one?<\/li>\n
- How soon<\/strong> do they get the results<\/strong>?<\/li>\n
- If 100 people get tested, how many results come back positive<\/strong>? (The\u00a0idea is that if it’s more than a handful, there are probably a lot more infected people you haven’t found yet, and you should be aiming to do more tests.)<\/li>\n<\/ul>\n<\/div>\n<\/li>\n<\/ul>\n<\/div>\n
In\u00a0the rest of this article, I\u00a0shan’t bring in much different stuff – I’ll just spell out the reasoning in a more step-by-step way, and give links to find out more.<\/p>\n
<\/a> Simple example of a tricky question<\/h2>\n
The\u00a0first thing I want to explain is: with statistics, some tricky questions never go away however expert you are. I\u00a0would even say that the art of understanding stats is largely the understanding of all the many many ways they can get wiggly :-)<\/p>\n
Here’s an example: if\u00a0you’re counting apples in your kitchen, and you’ve got four apples, but one is half manky already… would you count the half-manky one, so you’d say you had 4? or not, so you’d say you had 3?<\/p>\n
If you were counting up to check that your receipt from the shop was correct, you probably would<\/em> count the half-gone one. You\u00a0did buy<\/em>\u00a0it, even if you don’t get to eat all of\u00a0it. So\u00a0then the answer is\u00a04.<\/p>\n
But\u00a0if you were counting up to see how many days you could have an apple for a snack, you probably wouldn’t<\/em> want to count that one. Or you might count it as “a half”, because you could cut the squidgy bit off and eat the other half. So\u00a0then the answer is either 3, or\u00a03\u00bd.<\/p>\n
So\u00a0even with that relatively simple example, you’re already dealing with a question of: “what are we counting exactly, and why does it make sense to do it that way<\/strong>“.<\/p>\n
This kind of question comes up in stats all the time – including with the covid numbers.<\/p>\n
<\/a>Simple example of another tricky question<\/h2>\n
Another type of uncertainty is where there was<\/em> a definite answer, but it didn’t get noted at the time, and now you can’t find it out.<\/p>\n
For example, you might go swimming at a pool one day, and swim up and down. And later you think, I\u00a0wonder how many lengths I swam?<\/p>\n
There was<\/em> an answer. You can probably even guess roughly what it was, from memory or from the amount of time you were at the pool. “Maybe about 15 or 20, definitely not as many as 50.”<\/p>\n
But\u00a0if you didn’t count the exact number at the time, you don’t know it now. You can’t go back in time<\/strong> and watch yourself swim.<\/p>\n
This is a bit like the situation where someone died of a stroke back in February and now we’re wondering whether the stroke could’ve been caused by covid. If we could go back in time, we could test their body for the virus. But\u00a0now we can’t.<\/p>\n
The\u00a0more you get into stats geekery, the more you bump into things like those two examples! where there’s either uncertainty, or a “what makes sense here” situation, or both. Even the experts don’t always agree.<\/p>\n
For now, though, let’s get into the real questions about covid.<\/p>\n
<\/a>What counts as a death from covid<\/h2>\n
As soon as you ask the question of how\u00a0many people are dying of the illness<\/strong>, you have to decide what counts as “dying from covid”.<\/p>\n
In\u00a0some cases, it’s really obvious. The\u00a0person was fine until they got ill; after a week or so of feeling ill, they had trouble breathing; they went to hospital; a\u00a0test result said the virus was in their body; after a couple more weeks, they died. Definitely counts.<\/p>\n
In\u00a0some cases, it’s not so clear-cut.<\/p>\n
<\/a>When the test doesn’t confirm<\/h3>\n
For example: Someone died, and it looked<\/em> as though they had the illness, but the test result came back negative.<\/p>\n
\n- \n
- Was the test wrong? That can happen.<\/li>\n
- Was the illness really something else? That\u00a0can happen too.<\/li>\n<\/ul>\n<\/div>\n
<\/a>What if they would’ve died anyway<\/h3>\n
Suppose someone has a stroke, and dies. That gets written down as: they died of a stroke.<\/p>\n
Most strokes are caused by a blood clot getting stuck and cutting off the blood supply to a bit of the brain. (a few are caused a different way.)<\/p>\n
We know that covid can cause blood-clotting in the wrong places (or as doctors call it, “thrombosis”),2<\/a><\/b><\/sup> and some people with covid infections have had strokes.<\/p>\n
What if this person’s blood clot was caused by the coronavirus affecting their blood? Then if the person hadn’t<\/em> caught the coronavirus, their blood wouldn’t have formed that clot, and they wouldn’t have had the stroke.<\/p>\n
How do you tell that apart from a stroke they would’ve had anyway?<\/p>\n
Even when you know they had the covid virus at the time… strokes do happen without covid too. You\u00a0might wonder.<\/p>\n
<\/a>Clues from around the place<\/h3>\n
Another question you might have to think about is: are you going to allow clues from what’s going on around<\/em> the person who died?<\/p>\n
For example, let’s imagine that you’re a doctor looking after some people in a care home. And one day, one of the people you look after there gets ill with pneumonia – inflamed lungs – and it gets worse, and a bit later, they die.<\/p>\n
If that’s all<\/em> you know, you might put on the certificate “died of pneumonia”.3<\/a><\/b><\/sup><\/p>\n
But\u00a0what if you also know that two other people died of pneumonia in the same care home that week? and those two people were both tested for the covid virus, and it came back that they did<\/em> have it?<\/p>\n
Knowing that covid often causes pneumonia, you’re probably going to put that those<\/em> two did<\/em> die of covid – or to be specific, something more like “pneumonia caused by covid”.<\/p>\n
Then you’re thinking about that first person. Should you count their death as covid-related as well? now you know that covid was in their care home, and that person had the same symptoms as the other two? even though that one person for some reason didn’t get tested?<\/p>\n
<\/a>Definitions, choices and wiggle room<\/h2>\n
So, when you count up the covid deaths, whenever you get to one of those choices which could reasonably go in either direction, someone<\/em> has to decide whether it does count or it\u00a0doesn’t<\/strong>. (same\u00a0as, in the apples example<\/a>, you’d have to decide whether to count that half-an-apple or not.)<\/p>\n
This “human judgement call<\/strong>” factor is part of the reason why it’s hard to compare between different countries. The\u00a0people who define the counting-up rules in one<\/em> country aren’t necessarily making the same judgement calls as the people in another<\/em> country.<\/p>\n
If your priority is “we must definitely keep track of what’s going on, and not be lulled into a false sense of security”, then you make a big effort to offer testing to anyone who’s been near to an infected person. And\u00a0if you suspect that a death is probably<\/em> due to covid, you do<\/em> count it, even if you’re not 100% sure.<\/p>\n
For example, in Belgium, if\u00a0someone dies in a care home and doctors think it was covid, that gets counted as a covid death<\/a>, even if the person who died wasn’t tested.<\/p>\n
“It’s\u00a0based on the assessment of the medical doctor, usually taking into account whether the coronavirus is present in the same care home,” says Prof Van Gucht.<\/p>\n
“For example: if you have one or two confirmed cases, then the week after you have 10 deaths in the same home based on similar symptoms.”<\/p><\/blockquote>\n
In\u00a0other words, Belgium is an example where people are “erring on the safe side<\/strong>” in their counting. The\u00a0numbers might “look worse” than some other countries – but the medics and government there aren’t going to be caught out with “uh\u00a0oh, actually there were lots more infections we hadn’t realised were there”.<\/p>\n
On the other hand, if\u00a0your area relies on tourism… or you just want your government to look better… or for whatever reason, you decide you want to make the covid deaths look as low as possible, without actually going so far as to write down fake numbers… then you’d want to err on the side of counting the “uncertain” deaths as something else<\/strong>. You might even intentionally not<\/em> test people, so as not to find out for sure.<\/p>\n
“This\u00a0person died of pneumonia.” Yeah they did, but why did they get<\/em> the pneumonia? If there’s suddenly thousands more people dying of pneumonia than last year… that’s a bit suspicious!<\/p>\n
Or of course, you can equally well have a setup where nobody’s actively trying<\/em> to wiggle the figures, but they just have a testing system that doesn’t work very well<\/strong>, so it misses a lot of the people.<\/p>\n
Here’s an article with a chart showing how different countries have been defining and counting “deaths from covid”<\/a>.<\/p>\n
Here’s an article discussing similar “what are we counting exactly” questions in the US<\/a>.<\/p>\n
<\/a>England’s definitions of a covid death<\/h2>\n
As I understand it, there are two sets of official covid death numbers for England.<\/p>\n
\n- \n
- One set of numbers is based on counting who’s died after testing positive for the virus<\/strong>. It\u00a0covers the whole UK, and there’s a separate subtotal for England. It’s published by the Department of Health and Social Care (DHSC), based on input from Public Health England (PHE) and similar organisations. The latest total is at coronavirus.data.gov.uk<\/a>.4<\/a><\/b><\/sup> At 19 July 2020, their count stands at 45,300<\/strong> “positive-tested deaths” for the UK as a whole, of which 40,706<\/strong> were in England, 1,547<\/strong> in Wales, 2,491 in Scotland, 556 in Northern Ireland.<\/li>\n
- The other set is based on what doctors said on death certificates<\/strong>. That one is organised by the Office of National Statistics<\/strong> (ONS), which keeps track of all the births and deaths in England and Wales. When you register a birth or a death in England, the info gets sent to them.Their count isn’t published as often. The latest I’ve seen is from 3\u00a0July, published 14\u00a0July<\/a>: 50,548<\/strong> deaths registered, in England and Wales put together, which had covid on the death certificate.In practice, so far, most of those had covid identified as the main<\/em> cause of death.
\nIn the majority of cases (46,736 deaths, 92.8%) where COVID-19 was mentioned on the death certificate, it\u00a0was found to be the underlying cause of death.<\/p><\/blockquote>\n
But it can<\/em> also include certificates where covid got a mention as a contributing factor. (See longer quote from them below, explaining how death certificates work.)<\/li>\n<\/ul>\n<\/div>\n
You can see that the “death certificates” count is coming out higher than the “had a positive test before dying” count.<\/p>\n
Let’s look at how each organisation defines the numbers they’re counting.<\/p>\n
<\/a>DHSC definition<\/h3>\n
The definition in use (at 19\u00a0July) by the Department of Health and Social Care<\/strong> is summarised by this line, on the web page next to the total:<\/p>\n
Deaths of people who have had a positive test result<\/p><\/blockquote>\n
The full definition (as of 19\u00a0July) says more:<\/p>\n
Total number of deaths of people who have had a positive test result for COVID-19 reported on or up to the latest reporting date.<\/p>\n
The data do not include deaths of people who had COVID-19 but had not been tested or people who had been tested negative and subsequently caught the virus and died.<\/p>\n
Deaths of people who have tested positively for COVID-19 could in some cases be due to a different cause.<\/p>\n
– https:\/\/coronavirus-staging.data.gov.uk\/about-data#daily-and-cumulative-covid19-associated-deaths<\/a><\/span><\/p><\/blockquote>\n
(The full definition also includes an explanation of where exactly they get the data from in each UK nation, and other practical details.)<\/p>\n
So\u00a0if\u00a0you have someone who, going purely by common sense, might<\/em> have died because of covid, but for whatever reason they didn’t get tested, they wouldn’t be included<\/strong> in this official count. (This probably applied to a lot of people in March and April. More on that in a bit.)<\/p>\n
It also means that if someone’s cause of death doesn’t<\/em> look like covid, but they’d tested positive around the time of their death, they would<\/em> be included<\/strong> in the count.<\/p>\n
When the test has been recent<\/strong>, that’s maybe not as daft as it sounds, given how many weird ways covid turns out to affect people<\/a>:<\/p>\n
One colleague told Belchetz about a patient who came in with a head laceration. \u201cEveryone assumed it was nothing to worry about,\u201d he said. Head wounds are bread and butter stuff in the ER. But\u00a0after some detailed questioning, the patient revealed how he got the cut: He had passed out and fallen.<\/p>\n
He didn\u2019t have a cough or a fever. But\u00a0he wasn\u2019t getting enough oxygen. He got swabbed. The\u00a0test came back. He had COVID-19.<\/p><\/blockquote>\n
I’ve seen people (online) saying things like “my uncle died of a heart attack, and they’ve written down it was covid!” or “my grandma died from a bad fall and they’ve counted that as a covid death! ridiculous!”<\/p>\n
And, OK, if you could go and ask God, or replay a moving microscope scan of exactly what the person’s immune system was busy with when they died, then you might discover in some cases that the conclusion was wrong<\/em><\/strong>. But\u00a0if they had the virus at the time, it isn’t all that<\/em> ridiculous<\/strong>, because we know now that heart attacks and bad falls are<\/em> both things that can be (partly) caused by covid. In a situation where you can’t be 100% sure, it’s not unreasonable to guess that there could’ve been a connection.<\/p>\n
However, this “anything that happens after the test” definition will produce more mistakes as the test result recedes into the past<\/strong>. If someone had a minor run-in with covid six months ago, felt pretty much back to normal after a few weeks, and then dies of something apparently unrelated… does it really make sense to count that death as part of tracking the epidemic? Probably usually not.<\/p>\n
So the latest news about how they’re counting it is that there’s probably going to be a cut-off point in time for making the connection: for example, if the person’s positive test result was a month ago, or three months ago (I don’t know what timing they’re going to choose), don’t count that death as covid-related.<\/p>\n
The Secretary of State has today, 17\u00a0July, asked PHE to urgently review their estimation of daily death statistics. Currently the daily deaths measure counts all people who have tested positive for coronavirus and since died, with no cut-off between time of testing and date of death. There have been claims that the lack of cut-off may distort the current daily deaths number. We are therefore pausing the publication of the daily figure while this is resolved.<\/p>\n
(from https:\/\/www.gov.uk\/guidance\/coronavirus-covid-19-information-for-the-public#dashboard-of-coronavirus-cases-and-deaths<\/a> on 18\u00a0July, although by 19\u00a0July, the\u00a0wording had already changed a bit.)<\/span><\/p><\/blockquote>\n
Bear in mind, a time cut-off can’t totally solve the problem either<\/strong>! A\u00a0person could test positive while feeling fine, and next day, sheer bad luck for them, a builders’ crane tips over and crashes into their house and they die. You don’t really<\/em> want to count that as a covid death, but it would still be included under the time cut-off rule.<\/p>\n
Or, other way round: a person could die of a non-covid pneumonia, a year or two into the future after they’d had covid – and covid actually could<\/em> still have contributed to their death, if it had left lasting damage in their lungs.<\/p>\n
<\/a>ONS definition, and how death certificates work<\/h3>\n
Now, what about the definition in use by the Office of National Statistics<\/strong>?<\/p>\n
Here’s their explanation of how COVID-19 might end up on a death certificate<\/strong>, and the categories they use when they’re counting (bold type added by me):<\/p>\n
The doctor certifying a death can list all causes in the chain of events that led to the death and pre-existing conditions that may have contributed to the death. Using this information, we determine an underlying cause of death. More information on this process can be found in our user guide. In the majority of cases (46,736 deaths, 92.8%) where COVID-19 was mentioned on the death certificate, it\u00a0was found to be the underlying cause of death.<\/p>\n
Our definition of COVID-19 includes some cases where the certifying doctor suspected the death involved COVID-19 but was not certain, for example, because no test was done. Of the 46,736 deaths with an underlying cause of COVID-19, 3,763 (8.1%) were classified as \u201csuspected\u201d COVID-19. Including mentions, \u201csuspected\u201d COVID-19 was recorded on 8.4% (4,251\u00a0deaths) of all deaths involving COVID-19.<\/p>\n
In this bulletin, we use the term \u201cdue to COVID-19<\/strong>\u201d when referring only to deaths with an underlying cause of death as COVID-19 and we use the term \u201cinvolving COVID-19<\/strong>\u201d when referring to deaths that had COVID-19 mentioned anywhere on the death certificate, whether as an underlying cause or not.<\/p>\n
- The other set is based on what doctors said on death certificates<\/strong>. That one is organised by the Office of National Statistics<\/strong> (ONS), which keeps track of all the births and deaths in England and Wales. When you register a birth or a death in England, the info gets sent to them.Their count isn’t published as often. The latest I’ve seen is from 3\u00a0July, published 14\u00a0July<\/a>: 50,548<\/strong> deaths registered, in England and Wales put together, which had covid on the death certificate.In practice, so far, most of those had covid identified as the main<\/em> cause of death.
- One set of numbers is based on counting who’s died after testing positive for the virus<\/strong>. It\u00a0covers the whole UK, and there’s a separate subtotal for England. It’s published by the Department of Health and Social Care (DHSC), based on input from Public Health England (PHE) and similar organisations. The latest total is at coronavirus.data.gov.uk<\/a>.4<\/a><\/b><\/sup> At 19 July 2020, their count stands at 45,300<\/strong> “positive-tested deaths” for the UK as a whole, of which 40,706<\/strong> were in England, 1,547<\/strong> in Wales, 2,491 in Scotland, 556 in Northern Ireland.<\/li>\n
- How soon<\/strong> do they get the results<\/strong>?<\/li>\n
- So far this year – mostly during April and May – about 67 to 69 thousand people in the UK<\/strong> have died<\/a> that we wouldn’t normally expect at that time of year. This is called the “Excess deaths<\/a>“.<\/li>\n
- More explanation<\/strong>? Don’t like statistics but do want to understand? Jump\u00a0from a key point to the particular topic you’re interested in, or browse through.<\/li>\n
![\"Sample](\"https:\/\/www.uncharted-worlds.org\/blog\/wp-content\/uploads\/2020\/07\/DeathCertificateSample-300x257.jpg\")
<\/a><\/div>\n