Results for “Tests” 662 found
Tyler and I have been pushing pooled testing for months. The primary benefit of pooled testing is obvious. If 1% are infected and we test 100 people individually we need 100 tests. If we split the group into five pools of twenty then if we’re lucky, we only need five tests. Of course, chances are that there will be some positives in at least one group and taking this into account we will require 23.2 tests on average (5 + (1 – (1 – .01)^20)*20*5). Thus, pooled testing reduces the number of needed tests by a factor of 4. Or to put it the other way, under these assumptions, pooled testing increases our effective test capacity by a factor of 4. That’s a big gain and well understood.
An important new paper from Augenblick, Kolstad, Obermeyer and Wang shows that the benefits of pooled testing go well beyond this primary benefit. Pooled testing works best when the prevalence rate is low. If 10% are infected, for example, then it’s quite likely that all five pools will have at least one positive test and thus you will still need nearly 100 tests (92.8 expected). But the reverse is also true. The lower the prevalence rate the fewer tests are needed. But this means that pooled testing is highly complementary to frequent testing. If you test frequently then the prevalence rate must be low because the people who tested negative yesterday are very likely to test negative today. Thus from the logic given above, the expected number of tests falls as you tests more frequently (per test-cohort).
Suppose instead that people are tested ten times as frequently. Testing individually at this frequency requires ten times the number of tests, for 1000 total tests. It is therefore natural think that group testing also requires ten times the number of tests, for more than 200 total tests. However, this estimation ignores the fact that testing ten times as frequently reduces the probability of infection at the point of each test (conditional on not being positive at previous test) from 1% to only around .1%. This drop in prevalence reduces the number of expected tests – given groups of 20 – to 6.9 at each of the ten testing points, such that the total number is only 69. That is, testing people 10 times as frequently only requires slightly more than three times the number of tests. Or, put in a different way, there is a “quantity discount” of around 65% by increasing frequency.
Peter Frazier, Yujia Zhang and Massey Cashore also point out that you could also do an array-protocol in which each person is tested twice but in two different groups–this doubles the number of initial tests but limits the number of false-positives (both tests must be positive) and the number of needed retests. (See figure.).
Moreover, we haven’t yet taken into account the point of testing which is to reduce the prevalence rate. If we test frequently we can reduce the prevalence rate by quickly isolating the infected population and by reducing the prevalence rate we reduce the number of needed tests. Indeed, under some parameters it’s possible to increase the frequency of testing and at the same time reduce the total number of tests!
We can do better yet if we group individuals whose risks are likely to be correlated. Consider an office building with five floors and 100 employees, 20 per floor. If the prevalence rate is 1% and we test people at random then we will need 23.2 tests on average, as before. But suppose that the virus is more likely to transmit to people who work on the same floor and now suppose that we pool each floor. Holding the total prevalence rate constant, we are now likely to have a zero prevalence rate on four floors and a 5% prevalence rate on one floor. We don’t know which floor but it doesn’t matter–the expected number of tests required now falls to 17.8.
The authors suggest using machine learning techniques to uncover correlations which is a good idea but much can be done simply by pooling families, co-workers, and so forth.
The government has failed miserably at controlling the pandemic. Tens of thousands of people have died who would have lived under a more competent government. The FDA only recently said they might allow pooled testing, if people ask nicely. Unbelievably, after telling us we don’t need masks (supposedly a noble lie to help limit shortages), the CDC is still disparaging testing of asymptomatic people (another noble lie?) which is absolutely disastrous. Paul Romer is correct, testing capacity won’t increase until we put soft drink money behind advance market commitments and start using techniques such as pooled testing. Fortunately or sadly, depending on how you look at it, it’s not too late to do better. Some universities are now proposing rapid, frequent testing using pooling. Harvard will test every three days. Cornell will test frequently. Delaware State will test weekly. Lets hope the idea spreads from the ivory tower.
Cases in the Nordic country have declined sharply over the past few days and on Tuesday only 283 new cases were recorded.
That contrasts with a torrid month of June when daily numbers ran as high as 1,800, eclipsing rates across much of Europe, even as deaths and hospitalisations continued to decline from peaks in April.
At the same time:
…weekly numbers for tests have more than doubled since late May, putting the country in the same bracket as extensively testing nations such as Germany.
Here is the steadily declining Swedish death rate. No need to point out that Denmark and Norway, with their early and swift responses, did much better yet. I am interested in what is the best way to model why Sweden is not doing much worse.
2. The Roy and Paul Romer WSJ “keep our schools open and test” ad. Yet the CDC recommends against entry testing for higher education, see these Bergstrom tweets. Deeply irresponsible.
3. The culture that was Finland — until now!
Schwitzgebel and Rust famously found that professors of ethics are no more ethical than other professors. Peter Singer being perhaps a famous exception to the rule. In follow-up research Schwitzgebel and psychologist Fiery Cushman tried to find philosophical arguments to change people’s willingness to donate to charity. They were unable to find any. But perhaps they just weren’t good at coming up with effective philosophical arguments. Thus, they challenged moral philosophers and psychologists to a contest:
Can you write a philosophical argument that effectively convinces research participants to donate money to charity?
By a philosophical argument they meant an argument and not an appeal to pity or emotion. No pictures of people clubbing baby seals. The contest had 100 entrants which were winnowed down in a series of tests.
The test had people read the arguments and then decide how much of a promised payment they would they like to give to charity. An average of $2.58 was contributed to charity (of $10) in the control group (no argument). The best argument increased giving by 54% to $3.98. Not bad.
Here’s the argument which won:
Many people in poor countries suffer from a condition called trachoma. Trachoma is the major cause of preventable blindness in the world. Trachoma starts with bacteria that get in the eyes of children, especially children living in hot and dusty conditions where hygiene is poor. If not treated, a child with trachoma bacteria will begin to suffer from blurred vision and will gradually go blind, though this process may take many years. A very cheap treatment is available that cures the condition before blindness develops. As little as $25, donated to an effective agency, can prevent someone going blind later in life.
How much would you pay to prevent your own child becoming blind? Most of us would pay $25,000, $250,000, or even more, if we could afford it. The suffering of children in poor countries must matter more than one-thousandth as much as the suffering of our own child. That’s why it is good to support one of the effective agencies that are preventing blindness from trachoma, and need more donations to reach more people.
Now here’s the kicker. The winning argument was submitted by Peter Singer and Matthew Lindauer. Singer is clearly screwing with Schwitzgebel’s research!
You can read some of other effective arguments here. I don’t think it’s an accident that the winning argument was the shortest and also the least purely philosophical. I’m not saying Singer and Lindauer cheated, but compared to the other arguments the Singer-Lindauer argument is concrete and by making people think of their own children, likely to arouse emotion. That too is a lesson.
From Nate Silver, I am smushing together his tweet storm:
Something to think about: re-openings have been occurring gradually since late April in different states/counties. If you had a metric averaging out how open different states are, it would likely show a fairly linear pattern. So why is there a nonlinear increase in cases now?
Obviously some of that gets to the nature of exponential growth. An R of 1.3 isn’t *that* different than an R of 1.1, but played out over a few weeks, it makes a lot of difference. Still, a more complete story probably includes premature re-openings coupled with other stuff.
What other stuff? Two things seem worth pointing out. First, there seems to be some correlation with greater spread in states where it’s hot and people are spending more time indoors with the AC on. That *is* a bit nonlinear; there’s much more demand for AC in June than May.
And second, the conversation around social distancing changed a lot in early June with the protests and Trump making plans to resume his rallies. And COVID was no longer the lead story. Not blaming anyone here. But the timing is pertinent if people felt like “lockdowns are over”.
Here is the link, including a good picture of how the demand for air conditioning rises.
3. “I like saber cuts and bold steps. I get bored.” Why one fellow left academia.
I have a question for you and/or your MR readers: what’s the smart way to use spare Covid testing capacity?
With the virus (currently) receding in many places fewer and fewer people are getting symptoms and seeking tests.
Even without a second wave in the next few months, we’ll need testing capacity again for the next flu season, when we’ll need to distinguish between flu patients and Covid patients.
How should we use spare testing capacity in the meantime? Increase random testing? Weekly tests for everyone in a single city? Weekly tests for everyone in particular economic sectors?
I would be grateful for your thoughts on this.
That is from O.L. My intuition (and I stress this is not a scientific answer in any way) is to test people who take elevators every day, to get a better sense of how risky elevators are. And then test systematically in other situations and professions to learn more about transmission mechanisms, for instance the subway when relevant, supermarket clerks, and so on. Test to generate better risk data. What do you all think?
As tourism slowly resumes around the world, many nations are still reluctant to open their borders fully – with Cambodia imposing perhaps the toughest entry requirements of any country.
The south-east Asian country is popular with backpackers, and most renowned for the Unesco-listed temple complex at Angkor Wat.
According to the latest Foreign Office bulletin on Cambodia, foreign travellers must pay a $3,000 (£2,400) deposit for “Covid-19 service charges” at the airport upon arrival.
What appears to be the first “coronavirus deposit” can be paid in cash or by credit card.
The FCO says: “Once deductions for services have been made, the remainder of the deposit will be returned.” But those deductions may be steep – especially if another passenger on the same flight happens to test positive for coronavirus.
So far, so good, perhaps you are keen to go. But here is the downside of the experience:
But if one passenger on their flight tests positive for coronavirus, everyone on the same flight is quarantined in government-approved accommodation for two weeks, at a cost of $1,176 including meals, laundry and “sanitary services”. They must also pay another $100 for a second Covid-19 test. This totals a further £1,021.
If the traveller happens to be the coronavirus-positive patient, they will have to take up to four tests at another $100 (£80) each, as well as $3,150 (£2,500) for treatment at the Khmer-Soviet Friendship Hospital in the capital, Phnom Penh.
…Cambodia also imposes a requirement for $50,000 (£40,000) of travel insurance cover for medical treatment.
If the unfortunate arrival passes away, the Foreign Office warns: “The cremation service charge is $1,500 [£1,200].”
Here is the full article, via Shaffin Shariff.
The common element to our twin crises is that many of the government agencies we thought were keeping us safe and secure—the CDC, the FDA, the Police–have either failed or, worse, have been revealed to be active creators of danger and insecurity. Alex Tabarrok.
Derek Thompson writing at The Atlantic uses my quote as a jumping off point for a good piece on the failure of American institutions. He does a good job of covering the failures of the CDC, the FDA and the police but most interestingly asks why the FED has acted very differently.
While too many American police are escalating encounters like it’s 1990, and the FDA is slow-playing regulatory approval as if these are normal times, and the CDC is somehow still using fax machines, the Federal Reserve has junked old shibboleths about inflation and deficit spending and embraced a policy that might have scandalized mainstream economists in the 1990s. Rejecting the status-quo bias that plagues so many institutions, this 106-year-old is still changing with the world.
Why haven’t other American institutions done the same? Perhaps America’s dependency on old leadership makes our institutions exquisitely responsive to the anxieties and illusions of old Americans. Perhaps the nature of large bureaucracies is to become lost in the labyrinth of mission-creeping path dependency. Perhaps years of political polarization and right-wing anti-science, anti-expertise sentiments have wrung all of the fast-twitch smarts out of the government. Or perhaps we should just blame Trump, that sub-institutional creature summoned from the bilious id of an electorate that lost faith in elites when elites lost their grip on reality.
Whatever the true cause for our failure, when I look at the twin catastrophes of this annus horribilis, the plague and the police protests, what strikes me is that America’s safekeeping institutions have forgotten how to properly see the threats of the 21st century and move quickly to respond to them. Those who deny history may be doomed to repeat it. But those who deny the present are just doomed.
I see three reasons why the FED may have been different. First, the FED is one of the most independent agencies which may help to explain its faster and more adaptive behavior ala Garett Jones’s 10% Less Democracy. Second, and relatedly, the FED pulls a lot of leadership and staff from academia. That gives FED staff an affiliation goal and clique outside of politics which creates mental independence as well as political independence. Third, the FED was also tested in the last crisis and experience with crises helps as we have also seen in Asia tested by H1N1, SARS and MERS more than the US was.
I am not sure which, if any, of these explanations is the most important but I do think that we have a lot more to learn from comparative institutional analysis not just within the US but across countries as well.
4. “Even when controlling for density, counties with a high proportion of #Trump voters have lower cases and deaths.” Link here. And an argument that the protests increased net stay at home behavior.
8. Possible evidence of different Covid-19 strains? Not yet confirmed, use with care, but at least appears that it might be serious work.
3. The Poetry Foundation purge seems to me perhaps the weirdest purge — what exactly did they do wrong? (NYT)
6. My talk to Jason Crawford’s Progress Studies group. SoundCloud here.
While police officers may forgo mask-wearing for any number of reasons, from peer pressure within ranks that are loath to change to a desire to more easily communicate, the images have fueled a perception of the police as arrogant and dismissive of protesters’ health — perhaps even at the peril of their own.
And while several officers have conspicuously knelt down with or hugged people at rallies, the widespread failure to use masks is creating a more standoffish look, one that protesters say suggests that the police operate above the rules — one of the very beliefs motivating the nationwide movement.
“If you’re out here to protect the public, it starts with you,” said Chaka McKell, 46, a carpenter from Bedford-Stuyvesant who attended a protest in Downtown Brooklyn on Monday. “The head sets the example for the tail.”
The official New York Police Department policy is that officers should wear masks when interacting with the public. But in a statement on Wednesday, the department dismissed the criticism about the lack of masks as petty.
“Perhaps it was the heat,” Sgt. Jessica McRorie of the department’s press office said in a statement. “Perhaps it was the 15 hour tours, wearing bullet resistant vests in the sun. Perhaps it was the helmets. With everything New York City has been through in the past two weeks and everything we are working toward together, we can put our energy to a better use.”
“In a nutshell,” as they say, and here is the full NYT piece. This short vignette reflects two basic truths: first, there is a tendency to see oneself above at least some of the laws, and to follow defined procedures only selectively. Second, given the resources and constraints put on the table, such attitudes should not be entirely surprising.
When I was 12 it was one of my favorite books (by Peter Maas), and shortly thereafter I saw and liked the movie as well. On this viewing I was struck by the excellent understanding of the culture of corruption, the notion that the mayor is beholden to the police who can threaten to shirk, the performance of Al Pacino, and the wonderful scenes of early 1970s New York City (yes that is Soho you are seeing).
The last quarter of the film should have been shortened. And for all of its attempts to be a politically correct film, the degree of casual racism and sexism still is astonishing to the modern eye, specifically how either black criminals or attractive women are shown on screen.
Nonetheless recommended, and in particular as historical backdrop for understanding 2020. Here is a John Arnold thread on the primary of culture in police departments. And here is the police response to the recent protests.
I’ve been writing for years that the United States is underpoliced and overprisoned. Time for a review:
NYTimes: “The United States today is the only country I know of that spends more on prisons than police,” said Lawrence W. Sherman, an American criminologist on the faculties of the University of Maryland and Cambridge University in Britain. “In England and Wales, the spending on police is twice as high as on corrections. In Australia it’s more than three times higher. In Japan it’s seven times higher. Only in the United States is it lower, and only in our recent history.”
…Dr. Ludwig and Philip J. Cook, a Duke University economist, calculate that nationwide, money diverted from prison to policing would buy at least four times as much reduction in crime. They suggest shrinking the prison population by a quarter and using the savings to hire another 100,000 police officers.
Here’s a graph from Daniel Bier on the ratio of police to prison spending comparing the United States to Europe. The US spends relatively less on police and more on prisons than any European country.
And here’s a graph from President Obama’s CEA report on incarceration and the criminal justice system. The graph shows that the United States employs many more prison guards per-capita than does the rest of the world. Given our prison population that isn’t surprising. What is surprising is that on a per-capita basis we employ 35% fewer police than the world average. That’s crazy.
Our focus on prisons over police may be crazy but it is consistent with what I called Gary Becker’s Greatest Mistake, the idea that an optimal punishment system combines a low probability of being punished with a harsh punishment if caught. That theory runs counter to what I have called the good parenting theory of punishment in which optimal punishments are quick, clear, and consistent and because of that, need not be harsh.
Increasing the number of police on the street, for example, would increase capture rates and deter crime and by doing so it would also reduce the prison population. Indeed, in a survey of crime and policing that Jon Klick and I wrote in 2010 we found that a cost-benefit analysis would justify doubling the number of police on the street. We based our calculation not only on our own research from Washington DC but also on the research of many other economists which together provide a remarkably consistent estimate that a 10% increase in policing would reduce crime by 3 to 5%. Using our estimates, as well as those of some more recent papers, the Council of Economic Advisers also estimates big benefits (somewhat larger than ours) from an increase in policing. Moreover, what the CEA makes clear is that a dollar spent on policing is more effective at reducing crime than a dollar spent on imprisoning.
Can we increase the number of police? Not today but in recent years large majorities of blacks, hispanics and whites have said that they support hiring more police. It is true that blacks are more skeptical than whites of police and have every reason to be. Some of the communities most in need of more police are also communities with some of the worst policing problems. Better policing and more policing, however, complement one another. Demilitarize the police, end the war drugs, regulate people less, restrain police unions and eliminate qualified immunity so that police brutality can be punished and the bad apples removed and the demand for police will soar.
As we reform and unbundle policing let us remember that lower crime has been one of the greatest benefits to African American men over the past 30 years.
…the most disadvantaged people have gained the most from the reduction in violent crime.
Though homicide is not a common cause of death for most of the United States population, for African-American men between the ages of 15 and 34 it is the leading cause, which means that any change in the homicide rate has a disproportionate impact on them. The sociologist Michael Friedson and I calculated what the life expectancy would be today for blacks and whites had the homicide rate never shifted from its level in 1991. We found that the national decline in the homicide rate since then has increased the life expectancy of black men by roughly nine months.
…The everyday lived experience of urban poverty has also been transformed. Analyzing rates of violent victimization over time, I found that the poorest Americans today are victimized at about the same rate as the richest Americans were at the start of the 1990s. That means that a poor, unemployed city resident walking the streets of an average city today has about the same chance of being robbed, beaten up, stabbed or shot as a well-off urbanite in 1993. Living in poverty used to mean living with the constant threat of violence. In most of the country, that is no longer true.
More police on the street is one cause, among many, of lower crime. Chicago just had a horrendous day with 18 innocent people murdered in mostly random drive-by shootings, in part because the police were occupied with protests and riots. As we reform, unbundle, and reimagine, let’s be careful not to reverse nearly thirty years of falling crime which has produced a tremendous increase in the standard of living of the poorest Americans.
We need better policing so that we can all be comfortable with more policing.
1. Braintwister Bayesian chess doomsday arguments from Ken Regan. More about crime than chess per se.
4. Good vaccine and drug explainer (NYT).