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Potential false-positive rate among the 'asymptomatic infected individuals'
- nn35 7y agoHow did they estimate this? If anybody can read the actual paper, I’d love to know. If false positives dominate true positives then you’d expect total positives to depend primarily on number of tests given, right? Which sounds wrong to me, but I’d be interested in hearing other thoughts.
- nck4222 7y agoInteresting, as this means that China would be quarantining more people than "necessary", which would help slow the pandemic anyway. I can't imagine an asymptomatic person would put stress on the hospital system? But maybe I'm wrong there. I am curious if this also could indicate a false-positive problem with non asymptomatic people as well. False-positives are also why the CDC tests had to be shipped back, although that was because it was showing false positives in other diseases it was testing for, not COVID-19.
- bluGill 7y agoI'm starting to hear stories that the Chinese people demanded more quarantine than was needed. The problem got bad enough that the government decided to comply as it wouldn't hurt much more than the amount of quarantine was needed and might even help.
- Scarblac 7y agoI really wonder how we're going to look back at this in a few years. On the one hand, no matter what measures politics takes here (the Netherlands), every political party is clamouring for more. That suggests to me that we'll probably end up doing too much. On the other hand, the scenes from Hubei and Italy are horrific, we're going to get them here as well, it could be far worse, we absolutely must act now. On the third and fourth hands, the total number of deaths so far wouldn't even make a serious flu season in a single country, and fatality rates are all over the place depending on the country. Very confusing. Still, better too much than too little.
- ineedasername 7y agoThe thing is, if all these measures stop the spread, even if they were all justified, the outcomes are pretty much indistinguishable from an over reaction: both accurate response and over reaction have similar outcomes.
- eveningcoffee 7y agoCan you look up demographic of the infected people in Netherlands? It can be that you have somehow managed to avoid infecting older generation. I have longer discussion about this here http://www.savespain.eu/italy-vs-germany http://www.savespain.eu/italy-vs-germany
- gus_massa 7y ago> I can't imagine an asymptomatic person would put stress on the hospital system? If s/he is in the hospital in quarantine you must give blankets and food, probably a nurse to check the temperature and symptoms two or three times per day, a medical doctor one a day just to be sure. Perhaps a blood analysis from time to time? Luckily you don't have to handle visitors because they are in quarantine. (Or there are some visits? What if one patient tries to escape?) You must give an official reports for the family. Now you can assume the patient can send a WhatsApp message to the family saying s/he is fine, but you need probably still an official report. Paperwork, there is also paperwork. How isolated are them from each other. If they are all together, you can transform the overcrowded false positives in real patients.
- gpderetta 7y agowhy would an asymptomatic person be in an hospital? Even people with minor symptoms are asked to self quarantine at home pretty much everywhere.
- ineedasername 7y agoIn China, asymptomatic with a positive test result still put you in their make-shift hospital facilities.
- wycy 7y agoWould this indicate that the mortality rate is actually much higher percentage-wise, since the denominator is actually artificially inflated?
- andybak 7y agoI think so but wouldn't it also make the transmission rate estimates lower?
- wjnc 7y agoNot that I'd expect, since non-testing in probable positive cases (f.e. in NL those sick, but manageable and in home quarantine are usually not tested) seems to dwarf false-positives in negative cases.
- coding123 7y agoBut could that just be the flu.
- deleted 7y ago[deleted]
- etothet 7y agoThat was my thinking as well. I also wonder how many people who ARE symptomatic don't get tested and how much this balances out the false positives of asymptomatic people, if at all.
- lbj 7y agoIn Denmark we increased our testing 10-fold and found 300% more people infected. Our response to that increase has been to shut down the country completely for 2 weeks and expand our governments right to act: Forced entry into private property, forced isolation and treatment, forced testing. If this is all because of an error in the test kit I'm going to be super ticked off.
- mempko 7y agoOr think about it this way, this means as a percentage of real people infected, the mortality rate of COVID-19 is higher than thought. This false-positive rate means that the number of real cases is lower than reported and therefore mortality rate is higher. In other words, COVID-19 is more dangerous than thought if you catch it. Then again, I'm sure the actual cases dwarfs those reported since not everyone has been tested.
- glofish 7y agoMortality is almost always much lower than the initially reported and observed numbers. There could be many more people that never even get to the testing phase.
- gpderetta 7y agoAFAIK, that wasn't the case with SARS.
- ineedasername 7y agoThe same would be true of things like the Flu then too. Which means the true mortality rate of Flu is much lower, so even if COVID-19 is lower than current estimates for the same reason, it is still an order of magnitude higher than something like the Flu.
- dnautics 7y agoYes, and that's why absolute population normalized mortality rate is the only really comparable thing across populations.
- mempko 7y agoWait, so the actual mortality rate for COVID-19 is much higher than thought because of all the false positives on cases without symptoms?
- taborj 7y agoBut that also means that it doesn't spread as quickly/easily as originally thought. Right?
- glofish 7y agoit all depends what "higher than thought" means. If you mean the day-to-day numbers, those will always show variations, and paradoxically those will even show a substantial uptick once the spread slows down. The most vulnerable are affected first and most severely.
- cultus 7y agoOne fallacy that seems universal with healthcare folks is they think the false positive rate is the chance that a given positive result is erroneous. If an illness is rare, a positive result in a test with a 1% error rate might have an overwhelming probability of being a false positive. This is why prior probabilities need to be taken into account in making decisions.
- ses1984 7y ago>If an illness is rare, a positive result in a test with a 1% error rate might have an overwhelming probability of being a false positive. Can you elaborate on this a little more...?
- jbay808 7y agoIn the extreme case, imagine that nobody actually has the condition. Then every positive result is a false positive. The thing we call the "false positive" rate might still be only 1% though; that just means the test is correctly identifying 99% of people as negative and 1%, falsely, as positive.
- peterwoerner 7y agoThis is a classic result in Bayesian theory. Here is someone else explaining it. https://betterexplained.com/articles/an-intuitive-and-short-explanation-of-bayes-theorem/ https://betterexplained.com/articles/an-intuitive-and-short-...
- wool_gather 7y agoThat is a really excellent explanation. Thanks for sharing it.
- Cerium 7y agoIf a given test has a 1% chance of returning true, even when the actual result is false, then from a sample of say 1000 tests we would expect at least 10 trues, in addition to any actual true results. If the chance of having the disease in the general population is low (say 1 in a thousand for this example) then we would expect 11 true results in our thousand samples. Of which 91% are incorrect results - false positives.
- anaphor 7y agoCan someone clarify which type of test they analyzed? 80% seems way too high. I would expect something closer to 10% at most (which would still mean the probability of a true positive might be very low per Bayes' theorem)
- nn35 7y agoAre you confused or am I misreading your comment? The result is that 80% of positives are false positives, not that 80% of all tests are false positives. (IMO it is still fishy.)
- anaphor 7y agoI wasn't implying that 80% of all tests were false positives. I'm talking about P(You don't have coronavirus | You test positive). 80% is far beyond what would be normal for these types of medical diagnostic tests. I would expect something like 1% or less for a really good test, and around 10% for a bad one, but I don't know if the test the Chinese were using is really bad in some way, which is why I'm asking for clarification there.
- rossdavidh 7y ago80%...in asymptomatic cases. So if most of the people who get tested DID show symptoms, the false positive rate generally could be far worse. But, it would suggest downsides to more general testing.
- dnautics 7y agoBut if your diagnostic criteria is showing symptoms later, then you are ejecting the entire population of carriers who might be, say, teeming with the virus but showing zero symptoms, for perhaps a genetic or "dumb luck" reason.
- deleted 7y ago[deleted]
- nknealk 7y agoAnyone save the full text? Every time I try to get to it I get a 404.
- RobertDeNiro 7y agoI believe the full article is in Chinese.
- virusduck 7y agoIt's not in anything now. It's 404'd which is concerning.
- cs702 7y agoIf tests indeed have such a high false-positive rate, then all estimates of fatality rate calculated by dividing over the number of individuals identified as "infected" are too low, i.e., by implication the virus is actually deadlier than naively estimated. EDIT: All else remaining the same. See AnthonyMouse's comment below for important clarifications and corrections.
- AnthonyMouse 7y agoThat's assuming a large fraction of the people who have been tested are asymptomatic, otherwise a high false positive rate among asymptomatic people would have minimal effect on the numbers because they aren't being tested to begin with. Meanwhile you also have the opposite happening for the same reason -- if even a small percentage of asymptomatic people are actually infected but not being tested, a small percentage of "asymptomatic people" (i.e. nearly the entire population) could represent a very large proportion of those infected and cause the fatality rate estimates to be much higher than the true number.
- cs702 7y agoTrue. I updated my comment.
- andrewseanryan 7y agoOne big question is what percentage of positive tests are asymptomatic? If only a tiny percent are asymptomatic, then this false positive issue would not be elevating the total numbers much, right? I won’t claim to have the best resource here but one article stated: “ Dr. Tedros noted that only 1 percent of cases in China are reported as “asymptomatic.” And of that 1 percent, 75 percent do go on to develop symptoms.” https://arstechnica.com/science/2020/03/dont-panic-the-comprehensive-ars-technica-guide-to-the-coronavirus/2/ https://arstechnica.com/science/2020/03/dont-panic-the-compr...