– The goal of this videois to help us all estimatethe actual new COVID-19cases per day in your area. And it’s based onanalysis by Thomas Pueyo,he wrote an incredibleblog post on Medium. This is the link and I’ll also include itin the description below. This is the data that he usesto do some of his analysis. Now, some of you might be thinking,I know the number ofCOVID cases in my area,they’re reporting iton the news every day. But that’s the reported number of casesand that’s based on the peoplethat happened to get the test. There are a lot of people whomight not have symptoms yetor their symptoms are not severeenough to get the test yet. So the actual cases are likely far largerthan the number of confirmed cases. And we can see that in graphical form. Once again, this is a diagramput together by Thomas Pueyo. It’s a screenshot from his blog postwhich once again could be found here. This is all his analysis, orbased off of his analysis,but this shows you what washappening in Hubei Province,which is the province where Wuhan is. And there’s severalinteresting things here. The vertical axis is the number of casesand what we see on thehorizontal axis is per day. And so for example, wecould pick January 23. The yellow bar tells us thenumber of confirmed new casesthat day. So these are people whowould have been testedand then they tested positive,and it looks like thatnumber is about 300. But then we have this gray bar. This gray bar is the actualnumber of new cases that day,which is close to 2,500. So roughly eight times as high. Now you might be saying,how did they know theactual number of casesif they didn’t test everyone?Well, the way they did that iswhen someone testedpositive, they asked them,when did you first get the symptoms?And if they said, Hey, I firstgot the symptoms 10 days ago,they would be included as a true new case. An actual new case 10 daysbefore that on January 13,so that Chinese officials were ableto actually make thesegray bars in hindsight,based on when people saidthey first got the symptoms. And there’s a lot of reallyinteresting information here. First of all, we can see that Wuhanwas shut down on January 23. So let’s draw a linebetween the pre shut downand post shut down. And you can see just as the city officialswere starting to see confirmed cases,the actual cases were far higher,but then they shut down the cityessentially significantlyslowing down the spread rate. And a few days later, the actual caseswhich were they were ableto calculate in hindsight,start to flatten out and then go down. But even though they were going down,the confirmed new cases continued to go upbecause there is a delay. You can even see thedelay right over here. And that is roughly the amount of timebetween when people show symptomsand they are actually tested. Now you might be saying, allright, this isn’t too bad. It looks like things eventuallybecame okay for Wuhan. But this is because they dida very serious shut down. If they did not do this shut downand slow the spread of the virus,you would have seen thisexponential growth continue. It’s also worth rememberingwhat I just drew this curve on. This isn’t the total number of cases. This is the number of new cases per day. If you want the total number of casesat a given point in time,you would have to sum upthe gray or the yellow barsdepending on whether you want to lookat actual or confirmed cases. So as of January 22, if you total upall of these gray bars overhere, as of January 22,you get approximately 12,000 cases,while if you add upall of the yellow bars,that is roughly only 444 confirmed cases. So before the city evenwent into shutdown,and this is what the Chinesedoing reasonably good testing,you had a far higher number of casesthan the confirmed caseswould make you believe. And as large as theratio is on a given daybefore the city shut down,between the number ofactual new cases per dayand the number of confirmednew cases per day,it’s probably higherin a lot of the geographies where we live,because we’re not testingas well as the Chinese did. For example. This is data once againcompiled by Thomas Pueyoon his blog post. This is just a screen capture of itand I’m really just giving his analysis. This shows the total test performed,and the tests performed permillion citizens as of March 3,and you can see for example,where I live the UnitedStates is not doing so well. And so the number of reported casesin places like the United Stateswhere we are really juststarting to ramp up testingis far understating the numberof actual cases out there. So how do we go about estimatingthe actual number of cases in our area?Well, once again, I’m goingto use Thomas’s analysis,we’re gonna be lookingat the number of deathsand estimations of mortality rate,time from infection to death,and how fast the virus actually spreads. So in other videos, I’ll talk more aboutsome of Thomas’s analysis. But for mortality rate,it’ll make the math simple. And this actually does seemto be a pretty good estimate,we can assume that there’sa 1% mortality rate,the reports are as low aspoint 0. 6% in South Korea,and then as high as roughly5% in places like Iran. But it looks like the higher numbersare where the hospitalsystem is being overwhelmed. And then the lower numbers at the 0. 6%,might not be fully accountingfor all of the mortalitythat will happen due to the casesthat are actually out there. So we’ll assume a mortality rate of 1%. The other thing we need to think aboutis the time from infectionto death in those 1% of caseswhere someone does die. And to figure that out,I will look at this data right over here. This top chart, and itcomes from this link,which Thomas cites. And I’ll give the linkin the description below. This is the incubation period. This is an estimate of the timefrom when someone gets infectedto when they start to show symptoms. And this estimate is roughly five days. And then once you see symptoms,how long does it take todeath in those 1% of cases,or whatever the percentage is?Well, there’s varying estimates,but it looks like tomake the numbers easy,we can estimate roughly 15 days. So one way to think about itis five days from infectionto showing the symptoms,and then another 15 days fromshowing the symptoms to deathfor a total of 20 daysfrom infection to death,in what we’re assuming the 1% of cases. So I’ll write 20 days. And now the other thingwe’re gonna estimateis the days to doubling,days to double. This is how long does ittake for the infectionto double in the population. And this is gonna be heavily dependenton what the population is doing,how dense they are, howmuch they’re interacting. But we’ll look at some of these estimates. And they’re in very different contexts. And the lower the doubling rate,that means a virus is spreading very fast. While if you have a populationthat’s doing all the right things,they’re taking all the precaution,the doubling rate will be lower. So we could look at aconservative estimateand take a higher doubling ratethan all of these estimates,it’ll make our math a little bit easier. Let’s just assume adoubling rate of five daysand I’m using slightly differentnumbers than Thomas used,but it will be indicativeand you can do the same analysiswith whatever estimatesthat you choose to do. So let’s assume five days to double,which might be conservative,especially for placeslike the United Stateswhere we have not takenanywhere near the actionof a place like China orSouth Korea, or Japan. So now let’s use these numbersto figure out what might actuallybe happening in our areasbased on the data thatwe are presented with. So let’s say that weunfortunately here on some day,that there is one death inour region or in our city. Now, based on our estimates,we’re saying that the averagetime from infection to deathis about 20 days. That means that that personwould have likely contractedthe virus roughly 20 days ago,20 days ago. And so I’m gonna make a timeline. This is 20 days ago, thiswould be 10 days ago,10 days ago, this would be 15 days ago,and then this would be five days ago. Now it’s possible thatthey were the only personwho contracted the virus on that day,and then they happen tounfortunately get very sickand then pass away 20 days later. But if we assume that themortality rate is roughly correct,it’s quite possible that 100people were infected that day. The person that we knowabout is that one in 100who actually gets sickenough to pass away. And so if we assume that on 20 days agothat not one person, but 100 people. So the actual number of peoplewho are infected that dayis 100 infected that day. Once again, because it’sa 1% mortality rate. If we assumed a 0. 5% mortality rate,then we would say, all right,there might have been 200people infected that day,0. 5% of whom get all theway to death 20 days later. If you assume a 5% mortality rate,which would be a veryunfortunate situation,but that is a mortalityrate that we are seeingin different parts of the world,then you would have say,well, maybe there were 20people infected that day. When you only have one or twoor three deaths in a regionthat will make theestimates more difficult. But as unfortunately,we are likely to see alarger number of deathsin various regionsthat will make thisthese backward estimatesmore and more reasonable. Now if the infection ratein the population doublesevery five days, whatis now going to happen?After five days, you’regoing to have 200 casesin your region, 200 cases. Now, these wouldn’t just be new cases,this would be the cumulativetotal number of casesdue to those hundred. Now, this is actually quite conservative,because this is assuming that those 100that were infected 20 days agoare the only infectedcases in your region. There might be other infected casesthat were infected before that date. But I’m just assuming that the hundredthat were infected thatday are the only casesto be conservative, and sothey double after five days,and then they’ll doubleagain after five more days. And so you will get to 400 casesafter five more days. And then you will, after five more days,you will have doubledand I can’t even fit iton the screen anymore. You’re going to have 800 casesand then that means today just by evidenceof that one death,you probably have on the order ofand I can’t even draw the whole bar,approximately 1,600 cases. And so this is just tobe a little bit soberingabout how serious this is,and how much the data that we actually getis actually lagging thecircumstances on the ground,particularly in placeslike the United States,where we are barely evengetting started testing. For example, in my county,which is Santa Clara County in California. We just had our second deathunfortunately reported yesterdayand there was another deathfive days before that. Now, there’s only under 100reported cases in my county,but based on this analysis,the actual number ofinfected persons in my countyis likely to be at least afactor of 10 more than that,and it could be as high as1,000, 2,000, 3,000 people. We won’t know for sureuntil we can do the typeof hindsight analysisthat the Chinese had,but this is to just remind us how seriousthe situation actually is. So the big takeaway hereis to take all of this very seriously,especially because themortality rate itself can changedepending on how well equippedthe hospital system canhandle the situation. If we all socially isolate andtake the proper precaution,the spread rate will lowerand we won’t overwhelmthe hospital system. And we’ll hopefully be ableto keep the mortality rateas low as possible. But if we don’t take the precaution,and if we’re just complacentbecause we see this lagging datathat’s being reported to usbecause of the lack of testingin places like the United States,then it’s very possiblethat we eventually overwhelmthe hospital systemin the next few weeks,which would cause themortality rate to go higher.