Monday, 4 July 2022

Afternoon roundup

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Friday, 1 July 2022

Test to Exit

My column in this week's Insights newsletter notes the deficiencies in the Ministry of Health's recommendations around RAT results and ending self-isolation. 

A NUMERACY QUIZ FOR THE MINISTRY OF HEALTH

Dr Eric Crampton insights Newsletter 1 July, 2022

Suppose your middle-schooler came home with a math assignment.

She was told to measure everyone in the house and report on heights. But checking over the assignment, something seemed odd. Your 190cm partner wasn’t included.

“Oh, our teacher explained that most people are between 150 cm and 180cm. If we got a measurement outside that range, there was no guarantee that they were really that tall, so we should just ignore it.”

You’d worry about the state of numeracy among teachers, right?

Sure, the average person will be within that range. Some random person isn’t likely to be 190 cm tall. If the assignment had asked, “Is it likely that the next person you meet is 190 cm tall?”, the answer should be no – unless you happen to live with a very tall person.

But conditional on having been measured at 190cm, it’s more likely that you’re a tall person than that it’s just measurement error. If the ruler said three metres, you’d probably want to triple-check the figures. But 190cm isn’t that uncommon.

Why do I bring this up?

Back in May, I asked the Ministry of Health why they’ve been telling people to ignore positive RAT results after seven days of isolation. The Ministry replied this week. They told me that because seven days is beyond the average period of infectiousness, the current health guidelines do not require a negative test to leave isolation.

It wasn’t a cost-benefit assessment. It was a failure in basic numeracy similar to our imaginary teacher’s error – but far more consequential.

Work published in JAMA Internal Medicine in April suggested at least 60% of people with a positive RAT result six days in are still infectious.

The Ministry doesn’t seem to have checked any of that. They instead looked at the average period of infectiousness and decided positive results after that period could be ignored.

So people will be heading out, after isolation, on official advice, and sharing their Covid gift with others.

Yale Covid testing expert Dr Anne Wyllie had described the Ministry’s advice as ‘dangerous misinformation’.

I don’t know whether the Ministry’s answer reflects general incompetence, declining numeracy more broadly, or a dangerous mutant strain combining the two.

Let’s hope the revised NCEA numeracy guidelines filter their way up into the Ministry of Health before more dangerous variants arrive.

I had been in touch with the Ministry prior to this seeking, by OIA, what evidence they might have had in support of their view that a positive RAT after 7 days could be ignored if you had been asymptomatic for a day. 

Their reply came through last week:


It sounded like they'd just decided that, because the average period of infectiousness is less than 7 days, positive results after that interval could be ignored. So I followed up with a query. 

From: Eric Crampton 
Sent: Monday, 27 June 2022 4:41 pm
To: OIA Requests <oiagr@health.govt.nz>
Subject: RE: Response to your request for official information ref: H202206643

Thank you for this.

I would like to check my interpretation of one part here.

You note that “Current research indicates that it is possible for individuals to test positive from RAT tests beyond the average infectious period. Therefore, the current health guidelines do not require a negative test… to leave isolation.”

There are of course two potential reasons why someone might test positive after the average period of infectiousness has passed.

It could be that their infectiousness has passed, and the RAT is providing a positive result despite a lack of infectiousness. This seems to be the scenario your advice considers the more likely. 

But it could also be that the person with a positive RAT is one of those whose period of infectiousness is longer than average. An average will include some people whose periods of infectiousness is very short, some with middling duration, and some very long. Relatively small proportions of people would clear infection far faster than average, and relatively small proportions of people would take far longer than average. 

I do not know how you established the window for average infectiousness. Let us suppose that it reflects the period after which 95% of people are no longer infectious – for sake of illustration. If a person returns a positive result after that window has passed, the conditional probability of that person being among the 5% with a longer infectiousness period has to be relatively high unless false positive rates are very high. I had understood RATs to have relatively low sensitivity but fairly high specificity – false positives are less likely than false negatives. 

Work published recently in JAMA found, six days after illness onset, 61% of participants returned a positive antigen test while 36% produced samples that could produce viable cultures – a not unreasonable measure of continued infectiousness. If the 36% with viable cultures were all within the 61% producing a positive RAT result, then the odds of being infectious, conditional on having a positive RAT six days after illness onset, seem to be on the order of 60% - better than even. And the likelihood of not being infectious, conditional on having a positive test, would be about 40%. 

It sounds like your current advice around testing to leave isolation is based only on an assessment of the average period of infectiousness, not on the probability of being infectious conditional on a positive RAT at the end of the isolation period. 

Could you please tell me if I am wrong, and point me to the specific studies you’d rely on if so? You’ve provided a bundle of links to lengthy MoH documents spanning a wide variety of issues around the state of play in the pandemic. I cannot tell which studies you’re relying on in determining that a positive result can be ignored at the end of an isolation period, or that a negative result is not required.

I note that I am very likely to write a column on this specific issue if I do not get clearer guidance putting my mind at ease about the current guidelines by the end of the week.
I didn't hear back quickly, so I followed up:
Hi MoH,

I have drafted the following as column to be published on Friday, but I really would like confirmation that this is indeed what you have done here. If there was some more detailed risk assessment floating around in the background on the “No need for a test to leave isolation” recommendation, I would really want to know about it so I can correct or bin the column.

The draft text is appended below.

Thanks!
Eric Crampton



A numeracy quiz for the Ministry of Health

Suppose your middle-schooler came home with a math assignment. 

She was told to measure everyone in the house and report on heights. But checking over the assignment, something seemed odd. Your 190cm partner wasn’t included.

“Oh, our teacher explained that most people are between 150 cm and 180cm. So if we got a measurement outside that range, there was no guarantee that they were really that tall, so we should just ignore it.”

You’d worry about the state of numeracy among teachers, right? 

Sure, the average person will be within that range. Some random person isn’t likely to be 190 cm tall. If the assignment had asked, “Is it likely that the next person you meet is 190 cm tall?”, the answer should be no – unless you happen to live with a very tall person. 

But conditional on having been measured at 190cm, it’s more likely that you’re a tall person than that it’s just measurement error. If the ruler said three metres, you’d probably want to triple-check the figures. But 190cm isn’t that uncommon. 

Why do I bring this up?

Back in May, I asked the Ministry of Health why they’ve been telling people to ignore positive RAT results after seven days of isolation. The Ministry replied this week. They told me that because seven days is beyond the average period of infectiousness, the current health guidelines do not require a negative test to leave isolation.

It wasn’t a cost-benefit assessment. It was a failure in basic numeracy similar to the error that the imaginary teacher might have made – but far more consequential. 

Work published in JAMA Internal Medicine in April suggested at least 60% of people with a positive RAT result six days in are still infectious. 

The Ministry doesn’t seem to have checked any of that. It instead seems like they looked at the average period of infectiousness and decided positive results after that period could be ignored.

So people will be heading out, after isolation, on official advice, and sharing their Covid gift with others. 

Yale Covid testing expert Dr Anne Wyllie had described the Ministry’s advice as ‘dangerous misinformation’. 

I don’t know whether the Ministry’s answer reflects general incompetence, declining numeracy more broadly, or a dangerous mutant strain combining the two. 

Let’s hope the revised NCEA numeracy guidelines filter their way up into the Ministry of Health before more dangerous variants arrive. 
The Ministry provided a statement that could be attributed to a spokesperson - I couldn't include it in the Insights column, but I let them know I'd include it here. They write:

Since the start of the COVID-19 pandemic, New Zealand has been in the fortunate position of being able to monitor developments overseas and this has informed our pandemic response. The Ministry’s assessment is that other countries make decisions on isolation periods depending on the stage of the pandemic and the level of infection in their communities. In New Zealand, at our stage in the pandemic and to support our approach to limit the impact of the spread of COVID on the health sector, the seven days isolation for cases of COVID helps appropriately manage that risk.

We know that isolation for cases is critically important to limit spread and seven days is supported by evidence and experience of other countries. In the United States, for instance, the Centers for Disease Control and Prevention, recommended in December shortening the isolation period to five days. The change was motivated by science demonstrating that the majority of SARS-CoV-2 transmission occurs early in the course of illness, generally in the 1-2 days prior to onset of symptoms and the 2-3 days after. You can read the CDC media statement: CDC Updates and Shortens Recommended Isolation and Quarantine Period for General Population | CDC Online Newsroom | CDC

Rapid antigen tests (RATs) are useful tools by which individuals can test to see if they are COVID-19 positive. But in terms of accuracy, RATs are not without their limitations and we have been aware of this from the beginning. Our guidance to people who have had COVID-19 and who continue to have symptoms and feel unwell upon completion of their seven days of isolation is to remain at home for 24 hours after their symptoms resolve.

Our advice to the Government on the current seven day isolation period was based on evidence that there is a decline in infectiousness of the Omicron variant over time, and that in most cases, transmission occurs within seven days. The Ministry also recognises the need to achieve a balance between effectively managing the pandemic and the flow-on effect that an extended period of isolation would have on the wider economy and the health workforce.

I entirely sympathise with the notion that there has to be a balancing: you wouldn't stick someone in isolation forever. That would be crazy. And, in the absence of a full-blown CBA, a rule-of-thumb could well suffice. If someone poses risk that's comparable to the level of risk of a random-draw member of the public, continued isolation can't be warranted. 

But that requires having a gauge of what that risk is. And a person who tests positive will not have the cohort average level of risk. That person will have the average level of riskiness of people who test positive. Which will be higher. 

There are lots more studies coming out showing increased duration of shedding of culturable virus. Like this one showing that somewhere between a fifth and a quarter of people are still shedding culturable virus at 10 days. If you send someone who's infectious back to work at 7 days, rather than keeping that person home until a negative RAT, those extra couple days' work have a decent likelihood of sending someone else into isolation for 7 days. 


 

Now you're not going to find a study that perfectly matches what NZ has in place. The rules here say "Isolate for seven days (but vague about whether that starts on noticing symptoms or on a positive RAT), then, if symptom-free for at least a day, you're out". 

So what you really need is the infectiousness of people who have provided a positive RAT after having been 1-day symptom free 7 days from the start of symptoms (and 7 days from the first positive RAT). 

And it wouldn't be all that hard to find out either. We have thousands of people who turn up positive every day. Get a thousand of them to agree to take a RAT every day and to have a sample taken every day. Among the set of people providing a positive RAT at day seven, and who'd been symptom free, what proportion of samples can be used to culture the virus? It feels like the kind of thing where you should be able to have results in three weeks, and could have been started back in May.

And it really feels like the Ministry just doesn't grok conditional probabilities. 

Thursday, 30 June 2022

Truly, it was the greatest century

DeLong on the Greatest Completed Century So Far

Briefly: very very roughly, approximately, and inadequately, on average what twenty workers were needed to do in 1870 with their eyes, fingers, thighs, brains, mouths, and ears, 1 worker was able to do in 2010.

It is also true that what one worker could do in 1870 required 20 in -6000. But that 20-fold amplification was an 8000-year creep rather than a 140-year sprint: a proportional growth rate of 0.04%/year rather than 2.1%/year. And from -6000 to 1870 the overwhelming bulk of the potential benefits for humans from that twentyfold upward creep of technological knowledge had been eaten up by growing resource scarcity: the land and other natural resources available to support 1 person in -6000 had to support 400 by 1870.

By contrast, the twentyfold post-1870 technological-progress wave had to deal not with a 200- but only a 6-fold multiplication of human numbers, leaving lots to be devoted to bringing about much higher average productivity.

Productivity increases really really matter. 

If there is one single nugget of insight that I want readers of my book Slouching Towards Utopia to permanently engrave on their brains, this is it: around 1870 the rate of technological progress and thus of potential wealth creation went into much higher gear. After 1870, humanity's deployed technological capabilities and thus potential prosperity doubled every thirty-five years—and with it came economic creative destruction that reduced old economic structures to rubble and built new ones, and did it again, and again, and again, every single generation. Before 1870? From 1770-1870 humanity's globally-deployed technological prowess had a doubling time of about 150 years—not 35. From 1500-1770 it had a doubling time of 500 years. And before 1500, we are looking at a doubling time of 2000 years. The difference between our world, in which technological progress creatively destroys and revolutionizes the economy every 35 years, and the world of Agrarian-Age antiquity in which the same proportional changes in technology and economy, and thus in polity and society, take not 35 but 2000 years is, I think, a master force shaping human history.

I want to hammer home the obvious to those who don't have exponential growth magnitudes in their immediate intellectual panoply: a twentyfold amplification of human technological prowess in 140 years is a REALLY BIG F---ING DEAL. To get an equivalent proportional jump in the other direction, you have to go back from 1870 to the Bronze Age— to the year -2000 or so. We are, proportionately, as separate in technology from the railroad's Golden Spike and the first transoceanic cables as those were from the earliest chariots and the sculptor of the dancing girl of Mohenjo-Daro:


Wednesday, 29 June 2022

A clarification on sugar taxes

A few weeks ago, Rachel Thomas at Stuff included a short bit from me on sugar taxes and a new WHO metastudy

The Spinoff provided a perhaps too short a summary of that in its daily newsletter. I'd sent them a brief note of clarification, figuring that it was too late to change anything since it's an emailed newsletter. But it's online, here

The question of a sugar tax cropped up again earlier this month. Rob Beaglehole from the NZ Dental Association argues we need to be proactive with a sugar reduction strategy because of the woeful state of water fluoridation in New Zealand. The New Zealand Initiative’s Eric Crampton says the evidence doesn’t support the argument that a tax would reduce consumption.

I'd sent a note through to them, in case the issue came up again. I'll copy it here, mildly edited:

Thanks for the mention in today’s bulletin.

No need to do anything about it, but more for any future ones.

The problem with a ton of sugar-tax studies is that they assume that any drop in spending on soda (often the only data they have – they know spend shares, but they don’t know consumption) means a drop in consumption. Some of the drop could be a drop in consumption, but some of it could be a shift to downmarket product or product that’s lower cost-per-unit.

Again – this problem comes in when researchers are using household spend data that surveys people about how much they spent on various things over the past period, then combines that spend data with some measure of average prices to try to estimate consumption. 

If you see that someone shifted from spending $20/week on soda before a tax to spending, say, $18 in total after a tax, is it because:

a) They had been spending $1/can before the tax and bought 20 of them per week, and reduced that to 9 cans at $2/can after the tax – huge decrease in consumption!

b) They had been spending $1/can before the tax and bought 20 of them, and shifted to buying four 2-litre bottles of home-brand soda at $4.50 after the tax – small increase in consumption!

c) Some unknown combination of the two?

The studies that have only spending data effectively assume that (a) is the only thing that’s happening. (c) is the most likely thing, but the studies can’t see it. 

So it isn’t that a tax doesn’t decrease consumption. It is likely to decrease consumption somewhat. It’s more that the campaigners assume gigantic effects on consumption, because when many people are doing (c) and some are only doing (b), the studies assume it’s all (a).

It’s a technical issue in how the estimates are undertaken. They don’t handle things well when there’s adjustment not just in quantity but also in price-point. John Gibson over at Waikato has demonstrated the problems with it. But so much of the literature just ignores the problem. And the WHO meta-study is just a complicated average across studies that did not exclude studies known to have this problem. An average that includes overestimates is going to be an overestimate.

RBNZ's obligations?

That strange speech from RBNZ Governor Orr a couple weeks ago

Jenny Ruth digs a bit.

From Business Desk, last week:

Robertson said the specifics of how RBNZ’s obligations relating to Māori-crown relations “are fulfilled and embedded in the bank’s core functions is the responsibility of the board and management". “In the 2020 letter of expectations that I sent to the RBNZ in my role as minister of finance, I noted that the bank’s Te Ao Māori strategy aligned with an expectation to embody the government’s collaborative approach to the Māori-crown relationship.”

I dunno. A down-the-line central banker might have replied with something like:

"A low and stable inflation rate, in combination with supervision of the financial sector mitigate risks of bank failure, is the single best thing a central bank can do for every community, Māori included. We know that both inflation and unemployment will have more severe consequences for lower income communities. Failing to maintain expectations that inflation will be within bounds over the medium term will not improve long-term unemployment, which is set by structural features of the economy. But it will harm communities with less ability to hedge against inflation risks."

In related closing-of-the-browser-tabs:

Tuesday, 28 June 2022

Len Cook on revisions to the Stats Act

I had a chat last week with former Government Statistician Len Cook about some proposed changes to the Statistics Act. A greater reliance on administrative data will see some of the Government Statistician's powers pushed down to Ministries and Agencies that might not be well placed to handle it. 

Cook covers it here as well:

Without notice by all but a scarce few, the independence of the government statistician and the transparency of government data sharing and use in New Zealand could change after this year.

The Minister of Statistics David Clark has managed to avoid the public scrutiny of the constitutional implications of the Data and Statistics Bill despite transparency being a proper expectation for such change by citizens in a democratic society.

I've not pored over the legislation, but if Cook says there's a big problem in Clause 17, and that that Clause can just be deleted without harming the rest of the legislation, Parliament ought to have a look at it. 

You can catch my chat with Cook here:

Bootleggers and Baptists - construction waste edition

Rochester political scientist William Riker celebrated great herestheticians - those adept at manipulating policy to serve their own interests. His book is classic and should be on every public policy syllabus

Newsroom reports on some superb herestheticians applying Bruce Yandle's lesson about bootleggers and baptists, and about the importance of raising rivals' costs in the construction sector.

If you're a construction behemoth, you can bear regulatory compliance costs a lot more easily than smaller competitors. If you're building at scale, you're probably already doing a better job in avoiding construction waste.

Construction waste going to landfill really isn't any kind of public policy problem. Tips can set tip fees that recover costs. 

That doesn't mean you can't make it a political problem. Lots of people don't understand how landfill pricing works and just hate the idea of waste - failing to realise that, sometimes, measures to reduce waste are more wasteful than bearing the waste. It's a combination of economic illiteracy and aesthetics. 

So here's what we then get:

In a rarely-seen consensus private and public players in the building industry are calling for greater government intervention on the vexing issue of construction waste

The Environment Select Committee will today hear its last submission on the topic it has been investigating for several months - how to deal with the three million tonnes of sector waste dumped in landfills annually.

About half of this is thought to be useable or recyclable.

Fletcher Building Residential and Development chief executive Steve Evans said as the country embarked on a massive bid to address the housing shortage, change was more than just a nice-to-have.

“I've been in this industry for a long time and regulations change behaviour. So you ask people to do things voluntarily and you will, of course, get those that are socially-minded or environmentally-minded, that will do it.

It would be excellent fodder as case study for any of the public policy schools - in a world in which they could recognise that this sort of thing is a problem. 

Not all of the push is crazy though. Updating the Building Act so that it's easier to re-use materials makes a lot of sense.  

But just think about the difference in cost that mandates like this would impose on small players as compared to the big guys. MBIE is helping to create another cartel, and simply doesn't care. 

Ministry of Business Innovation and Employment spokesperson Antonia Reid said a range of work was underway to encourage the reduction of waste, including investigating the barriers to reusing and recycling building materials and expanding the waste infrastructure network.

“MBIE is also progressing changes which would require reporting and measurement of new buildings’ whole-of-life embodied carbon emissions - from manufacturing building materials to disposing of them at the end of a building’s life.

“We expect this focus on embodied carbon reduction will encourage greater repair and retrofit of existing buildings, smarter building design to help minimise emissions and waste within new construction, and more deconstruction of buildings at the end of their lives if they cannot be made fit for purpose.”

For those unfamiliar with Yandle's Bootleggers & Baptists: