tag:blogger.com,1999:blog-582368152716771238.post2146401715572512421..comments2024-03-29T07:18:14.271-05:00Comments on The Grumpy Economist: Jacobin pandemicJohn H. Cochranehttp://www.blogger.com/profile/04842601651429471525noreply@blogger.comBlogger10125tag:blogger.com,1999:blog-582368152716771238.post-41715234147775174132020-10-29T11:44:19.768-05:002020-10-29T11:44:19.768-05:00Immunity is not conferred. The following story of...Immunity is not conferred. The following story of a Russian researcher's experience with the coronavirus is illustrative. He first contracted the virus on an airline flight from Paris, France, to Moscow and from Moscow to Siberia. His immune system produced antibodies; his symptoms were mild. He is a researcher and he underwent repeated testing for antibodies during this first illness. The concentration of antibodies diminished over a short period of time until there were no antibodies in his system.<br /><br />Being a researcher, he purposely exposed himself to 19 hospitalized patients with COVID-19. He was infected by the coronavirus a second time; and, this time the symptoms were more trying, but he survived.<br /><br />His first conclusion? -- there is no 'herd immunity' effect with this coronavirus.<br /><br />His second conclusion? -- adenoviral vector-based vaccines will not confer 'herd immunity'. <br /><br />Story: https://nationalpost.com/news/russian-professor-twice-infects-himself-with-covid-19-says-herd-immunity-wont-save-us<br /><br />Old Eagle Eyehttps://www.blogger.com/profile/05270080708077871311noreply@blogger.comtag:blogger.com,1999:blog-582368152716771238.post-36139002498174739402020-09-27T04:56:02.867-05:002020-09-27T04:56:02.867-05:00Your examples highlight the exact distinction John...Your examples highlight the exact distinction John is trying to make, though, between tests for the purposes of medical diagnosis and tests for public-health interventions. You have to apply decision theory and error-cost minimization to this problem. The sensitivity a test needs is directly proportional to the harm from a false negative (relative to a world without testing) and the specificity a test needs is directly proportion to the harm from a false positive (relative to a world without testing). So, in scenarios that you mention, where you are going to use the test to do something potentially dangerous if done to someone healthy, then absolutely you need tests with high specificity. For sure, no one should use a saliva test with low specificity to decide whether to give someone dexamethasone. <br /><br />But public-health interventions don't have the same harm profile. The risk to someone who receives a false positive is unnecessarily isolating for a couple weeks. That is inconvenient, but hardly dangerous. Especially so when the alternative to testing is a high degree of existing isolation.<br /><br />Similarly, the risk of a false negative is that a person spreads the virus. That is more dangerous, but one has to consider the alternative without testing. If the alternative without testing is a significant degree of social interaction with community spread, a test doesn't have to be very sensitive to help.<br /><br />Critically, this is true no matter how you strike the policy balance between the costs of social isolation and the costs of virus spread. For a community that has chosen maximal lockdown, the cost of false positives is de minimis, since everyone is essentially quarantined already, so the false positive rate can be sky high without much problem. On the other side, even a test that has a 50% false negative rate can help this community: it can now halve its social isolation while keeping the transmission rate the same.<br /><br />A community that has chosen "let it rip" can also benefit even from a very inaccurate test. A high false negative rate will have de minimis impact in this community, because no one is isolating anyway. On the other side, even a test with a high false positive rate can help this community: if people who take a test with 10% false positive rate just take basic precautions, transmission can fall dramatically with a relatively small number of people being inconvenienced.<br /><br />Real communities will be somewhere in between. But the point stands that the test produces benefits even when very inaccurate. For sure, the lower the false positive rate, the harsher the isolation you are likely to be able to sustainably impose on those who test positive or the fewer the people you will inconvenience; and the lower the false negative rate, the greater the relaxation of social isolation you can support or the lower the continuing transmission you will be able to achieve.<br /><br />South Korea is a good case study. They were able to rapidly introduce testing because they had a test kit designed to capture features common to all known coronaviruses. This test had terrible specificity. Huge numbers of people in South Korea were probably unnecessarily quarantined for a short period. But the benefits have been dramatic: life is much more relaxed than elsewhere while transmission is minimal. <br /><br />In addition, the cheaper the tests get, the more you can use multiple testing to compensate for flaws in the test's accuracy. For cheap tests with high false positive rates, multiple samples can be independently tested and a positive declared only when a sufficient number of them show positive. (Indeed, you could even calibrate precautions, a person with 1/5 positive must where a mask everywhere including at home, a person with 5/5 gets taken to a monitored quarantine facility.) For tests with high false negative rates, people can be tested more frequently.Dan Culleyhttps://www.blogger.com/profile/05478482975658606490noreply@blogger.comtag:blogger.com,1999:blog-582368152716771238.post-15299740865131501202020-09-23T14:46:21.985-05:002020-09-23T14:46:21.985-05:00"the most radical and ruthless of the politic..."the most radical and ruthless of the political groups formed in the wake of the French Revolution, and in association with Robespierre they instituted the Terror of 1793–4." As a member of the Committee of Public safety, Robespierre suborned terror all the while putting his own head at risk. Old Max met Madame Guillotine on the 28th of July, 1794. David Seltzernoreply@blogger.comtag:blogger.com,1999:blog-582368152716771238.post-58062671669596010952020-09-23T00:17:37.542-05:002020-09-23T00:17:37.542-05:00Why doesn't the administration say "free ...Why doesn't the administration say "free the tests?" My guess is a combination of (i) ignorance about the value and the way to accomplish that (which might not be easy) and (ii) concern about the short term political fallout of more cases. I'm not sure tests are a panacea, but I'd sure allow people to find out by "freeing the tests."DWAndersonhttps://www.blogger.com/profile/11912588081258797990noreply@blogger.comtag:blogger.com,1999:blog-582368152716771238.post-27903015851750462702020-09-22T17:38:41.417-05:002020-09-22T17:38:41.417-05:00I am always amazed whenever I read novel and impec...I am always amazed whenever I read novel and impeccable rhetoric on the "primal" nature of capitalism and the inexorable Orwellian dystopia it brings. <br /><br />James Carlylehttps://www.blogger.com/profile/06778250145758547603noreply@blogger.comtag:blogger.com,1999:blog-582368152716771238.post-54992038597337977452020-09-22T17:32:27.134-05:002020-09-22T17:32:27.134-05:00Right now we are acting as if everyone has tested ...Right now we are acting as if everyone has tested positive for the virus. I think flawed testing is better than no testing. It's not even clear that most people are complying with the sheltering place mandates. There are fans at football games.James Carlylehttps://www.blogger.com/profile/06778250145758547603noreply@blogger.comtag:blogger.com,1999:blog-582368152716771238.post-75136511346349678912020-09-22T16:40:38.630-05:002020-09-22T16:40:38.630-05:00So, let's conduct a gedankenexperiment, a la K...So, let's conduct a gedankenexperiment, a la Karl Shell, and imagine that you are a typical average American Joe. You wake up one morning feeling absolutely awful, your brain is in a 'fog', and your breathing is somewhat labored. You call your ex- and ask, "What should I do, honey?" She mulls that one over for a minute, and then replies, "Dear ex-, I've just finished reading about a grumpy economist's prescription for testing. Get yourself down to the nearest CVS, and buy one of those off-the-shelf 'COVID tests and follow the instructions. You know how to do that, Dear, don't you?" "Yes", you reply, "that's the solution!" So, you make your way to the nearest CVS, and you find the 'COVID' test products section--all over the counter stuff. There are ten different testing products, all for self-assessment, ranging in price from $9.99 through $95.98, per test. All are "guaranteed to work"; all are labelled "easy to use". Which one do you choose? The $9.99 one. So, you get home, you're feeling worse, but optimistic. You follow the directions and self-administer the test. You wait the stipulated 15 minutes for the device to cough up the test result. "Negative" for COVID-19, it states. "Whew!", you say, "You had me worried for a while there." Still, you're feeling worse now than ever before. Your breathing is more labored now than before. Your mind is in a deeper fog. You head to the couch to lie down for a spell. You've been sold a bill of goods. Snake oil, the real thing. No FDA, no guaranteed reliable results. Your ex- comes over and finds you laid out cold on the carpet--you never made it to the couch. 9-1-1 it is, and there you go, just another vital statistic. Such is life. You pay your money, and what do you get in return?--zilch. No FDA, no guarantee.Old Eagle Eyehttps://www.blogger.com/profile/05270080708077871311noreply@blogger.comtag:blogger.com,1999:blog-582368152716771238.post-6071599517982460282020-09-22T16:11:00.340-05:002020-09-22T16:11:00.340-05:00Apologies, that should be Romer (rather than SumNe...Apologies, that should be Romer (rather than SumNer). But the point stands.Stephen Ramsdenhttps://www.blogger.com/profile/07772744008763302189noreply@blogger.comtag:blogger.com,1999:blog-582368152716771238.post-43536615831153974182020-09-22T14:33:49.552-05:002020-09-22T14:33:49.552-05:00Speaking as an average person I very much agree wi...Speaking as an average person I very much agree with the Scott Summer / Alex T view. But clearly, for reasons that you outline in a number of your posts, this isn't happening. Anywhere.<br /><br />Can we start something? E.g. in the US, is it impossible to get a low cost saliva based test? Would you be breaking the law? Is there a work around? It seems to me that if a few high profile people took this up it might catch (so to speak). I don't mean talking about it, I mean doing it. High profile is not thee and me - although it would be a start. But it needs some widely well known folks to get the ball rolling. Perhaps the US (and UK) are not the most promising places to start. But somewhere is. Stephen Ramsdenhttps://www.blogger.com/profile/07772744008763302189noreply@blogger.comtag:blogger.com,1999:blog-582368152716771238.post-55243173242044413932020-09-22T10:31:06.054-05:002020-09-22T10:31:06.054-05:00Did you really mean "relatively inaccurate&q...Did you really mean "relatively inaccurate"?<br /><br />"Go to CVS, get the test kit, find out if you have it. No referral, no doctor visit, no prescription, no insurance, no faxed paperwork. Let private decisions figure out what to do with the results." <br /><br />Do you think the average person understands concepts such as sensitivity and specificity? Can they be relied upon to make informed decisions? What if their decision conflicts with what I think their decision should be? Do they have the right to ignore using masks and social distancing based on their uninformed interpretation of questionable test results and run around spewing contagion?<br /><br />The priority needs to be focused on a test with high sensitivity and specificity and the results discussed with a physician. For example the straight leg test for sciatica is highly sensitive. If you have sciatica the odds of a positive SLR test is high. Unfortunately the SLR test is not very specific. Many people with a positive SLR do not have sciatica. Do you trust people to make their own diagnoses using SLR?<br /><br />My own experience has been two completely asymptomatic individuals who tested positive and another with cough and fever who tested negative 3 times before succumbing to COVID-19 about 2 weeks later. So much for testing.<br /><br />Suppose you get test results back that show your potassium is 5.8. If thats real, you have a medical emergency since that could lead to cardiac dysrhythmia. OTOH a high potassium might be due to rupture of red blood cells while the sample is drawn, resulting in a false high result. Two very different outcomes. How many people understand what to do with a potassium level of 5.8? I can tell you one thing: my accountant didn't know until he emailed me his results.<br /><br />First we need a test with high sensitivity and specificity. Then we need to know what to do with the information. The decision should not be left to the uninformed patient with a test kit not vetted by the FDA.Michael Gorbackhttps://www.blogger.com/profile/05789268342873061299noreply@blogger.com