5 ms·
> if you tested everyone using this strategy and quarantined those who tested positive, you'd eliminate Covid in two months. You have too much confidence in th
by nanis 6y ago
> if you tested everyone using this strategy and quarantined those who tested positive, you'd eliminate Covid in two months.
You have too much confidence in that statement.
If false positive, false negative, and prevalence rates are all 5%, and let's say you subject 350,000,000,000 people to the dog test (ignoring the time it takes to do that and logistical difficulties with having enough dogs and handlers etc).
9.5% of society tests positive resulting 33,250,000 total positive results. Half of this number are true positives and half are false positives. That means, quarantining 16,625,000 uninfected people along with 16,625,000 infected people which results in the loss to society of their output and might also now get them infected depending on how they are quarantined.
Out of the 17,500,000 people who are infected, there will be 875,000 false negatives who will not be quarantined who will continue to spread the infection. In fact, 5% false negative rate sounds kind of optimistic. If false negative rate is 25%, 4,375,000 infected people will not be detected using this method.
You can play with the numbers using this calculator[1].
Second, let's say you put a dog at every company and every day everyone needs to be sniffed on the way in. If the false positive rate is 5%, the probability that you will not be quarantined due to a false positive during the year is 0.95*250 approx = 0.0003%.
[1]: https://www.covid2020.icu/false-positive-false-negative-simulator/app.html?scenario=Test%20350%20million:%20prevelance,%20false%20positive%20and%20false%20negative%20all%205%25;sample_size=350000000;percent_infected=5;false_positive_probability=5;false_negative_probability=5 https://www.covid2020.icu/false-positive-false-negative-simu...
- NicoJuicy 6y agoIt's also possible to add real tests and not taking dog sniffing as a source of truth, but more as an indicator.
- nanis 6y ago"Real" tests are also subject to false positives and false negatives. What you are suggesting is to ignore the possibility that dog sniffing may result in false negatives, and administer a "real" test to anyone who's identified by a dog to be positive. Keep in mind that under reasonable assumptions, half of those people are false positives. A portion of them will falsely test positive again. However, some of the true dog test positives (anywhere between 2% - 25% of them) will falsely test negative. Therefore, this strategy will result in more infected people not being quarantined.
- NicoJuicy 6y agoBut way more people with covid will be quarantined than without those tests.
- scarmig 6y agoMy scenario was to give everyone the "always return positive" test, as suggested in the original comment, though it was ambiguous as stated. So there is no false negative rate, since there are no negatives. The magic doggy is just to encourage compliance. You do accurately describe the issue with relying solely on tests with false negatives to control Covid.
- nanis 6y ago> give everyone the "always return positive" test, I had assumed your comment was sarcastic. Note that if you believe prevalence is 95%, there is no reason to spend any resources on dogs, tests, or even vaccines. Making all that effort only makes sense in a world where prevalence is assumed to be low and the effort is to keep it low. So, let's say prevalence is 5%. Then, you method has a false positive rate of 95%. Are you OK with the implications of that?