Posts from February 2022 (24)

Stuff (from the Sydney Morning Herald) reports that a baby was born at exact 2:22 and 22 seconds on February 22nd. An Australian maths professor is quoted as saying

“It’s about 1 in 30 million is the chance of being born at that precise second,”

Maths nerds will recognise that as the number of seconds in a year (roughly π times ten million), and music nerds will remember 525,600 as the number of  minutes in a year and multiply by 60.  So, 1 in 30 million is the chance of picking a particular second if you pick one randomly from a year. It seems a bit strange to give that as the answer for the baby’s chance of being born at that precise time.

If you had picked this specific baby, Bodhi, in advance, his chance of being born at a particular second depends on how much variation there is in birth times.  They’re roughly a Normal distribution with a standard deviation of 16 days, and it turns out this gives a chance of about 2.5% of being born five days early and so about one in 3.6 million of being born in a particular second on that fifth day early.

But we didn’t pick this specific baby in advance and look at when he was born. We picked the time and looked for the baby. There are nearly 300,000 births per year in Australia; about one per 100 seconds.  There would be about a 1 in 100 chance that some baby in Australia is born at one particular second.

So far we’ve been saying there’s one particular second. But the baby was born at 14:22:22 and presumably 02:22:22 would have done just as well. Or maybe 22:02:22 or 22:22:22.  It’s not really one special second in the day.  And on top of that, a baby isn’t really born at a single second — there’s at least a small amount of flexibility in how you define the time, and you know someone is going to take advantage of the flexibility.  What would be really surprising would be a birth recorded as 2:22:19pm on 22/2/2022.

Team Ratings for Week 16

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 76 matches played, 53 of which were correctly predicted, a success rate of 69.7%.
Here are the predictions for last week’s games.

Predictions for Week 16

Here are the predictions for Week 16. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Round 19

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 122 matches played, 87 of which were correctly predicted, a success rate of 71.3%.
Here are the predictions for last week’s games.

Predictions for Round 19

Here are the predictions for Round 19. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Week 2

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 5 matches played, 4 of which were correctly predicted, a success rate of 80%.
Here are the predictions for last week’s games.

Predictions for Week 2

Here are the predictions for Week 2. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Round 18

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 100 matches played, 54 of which were correctly predicted, a success rate of 54%.
Here are the predictions for last week’s games.

Predictions for Round 18

Here are the predictions for Round 18. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Round 5

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 12 matches played, 9 of which were correctly predicted, a success rate of 75%.
Here are the predictions for last week’s games.

Predictions for Round 5

Here are the predictions for Round 5. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Back in November, I wrote

The Covid vaccine is safe and effective and it’s good that most eligible people are getting it. But how much protection does it give? If you look at the NZ statistics on who gets Covid, it seems to be extraordinarily effective: the chance of ending up with (diagnosed) Covid for an unvaccinated person is about 20 times higher than for a vaccinated person.

That’s probably an overestimate.

The issue was that during the Auckland Delta outbreak, unvaccinated people were probably more likely to be exposed to Covid than vaccinated people, and this was exaggerating the (real, but smaller) benefit of the vaccine.

Things have changed. The case diagnoses for vaccinated and unvaccinated people are about equal as a proportion of the population.  Partly this is because the vaccine is less effective against infection with Omicron, but now I think the social factors may well be leading to an underestimate of the vaccine benefit.  The point of the traffic-light system was to reduce virus exposure for unvaccinated people, both so they would be less likely to pass the virus on and so they’d be less likely to end up in hospital.  Reports in the news about unvaccinated people and about businesses that don’t like the system suggest that it does at least reduce the presence of unvaccinated adults in crowded indoor public settings.  You could reasonably expect, then, that unvaccinated adults are less exposed than vaccinated adults and that their equal case rate shows the vaccine is working.

In the absence of any other information it would be hard to decide how much to believe this explanation, but we do have other information. Other countries, with more cases and more data, have better estimates of the benefit of the vaccine than you can get from the published NZ data.  The vaccine does reduce infections with Omicron.  It doesn’t work as well as it did against Delta, and the benefit falls off more rapidly with time, but there is a benefit.   From the overseas data we’d expect the vaccine to working in New Zealand too, and the data we have are consistent with that expectation.

Even if we weren’t preventing cases of Omicron, there are at least two arguments for continuing to have vaccine rules. First, Delta is not actually gone — it’s still 5-7% of sequenced cases in MIQ and the community. It’s a small *fraction* of the outbreak, but the numbers haven’t gone down much. Second,  hospitalisation matters. As you may remember, we had hospitals even before Covid.  They’re important for treating everything from cancer to car crashes.  Keeping them available for non-Covid uses has always been a key motivation of the Covid strategy.

The numbers don’t decide anything; whether to change the rules is a policy question. But the inputs to policy should be the best estimates we can get of vaccine effectiveness, not the crude case counts.

• Stats NZ had to take down NZ.Stat, one of the main public interfaces to official statistics.  They’re being very helpful by email to people who need the data, but it’s a problem — and it’s not really the right interface for people who just wanted to look up a few numbers.  Eric Crampton wrote about why this matters (feel free to ignore the comments about wellbeing indicators)
• The NZ Open Source Assocation awards include one to the Ministry of Health for the Covid trace app, and to the University of Auckland Computational Evolution group for their phylogenetic inference software, BEAST
• Measuring things you don’t have any real way to interpret, from XKCD
  
• “Creepiness” Is the Wrong Way to Think About Privacy from Slate. It’s a useful heuristic, but it’s not an analysis.  As an illustration of how intuitions can be non-generalisable, the chair of George W. Bush’s bioethics council thought eating ice-cream in public was offensive.
• The power of selection bias: “In a series of tweets with an authentic February 7 timestamp, the self-described “industry insider working deep within Nintendo” showed an apparently deep foreknowledge of details that Nintendo wouldn’t officially reveal until the evening of February 9, two days later.”. He did it by making lots of predictions and then deleting all the ones that didn’t pan out.
• Tim Harford explains Arrow’s Impossibility Theorem: it’s hard to take a set of individual preferences and turn them into a group decision

Team Ratings for Week 15

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 71 matches played, 49 of which were correctly predicted, a success rate of 69%.
Here are the predictions for last week’s games.

Predictions for Week 15

Here are the predictions for Week 15. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.

Team Ratings for Round 18

The basic method is described on my Department home page.
Here are the team ratings prior to this week’s games, along with the ratings at the start of the season.

Performance So Far

So far there have been 115 matches played, 83 of which were correctly predicted, a success rate of 72.2%.
Here are the predictions for last week’s games.

Predictions for Round 18

Here are the predictions for Round 18. The prediction is my estimated expected points difference with a positive margin being a win to the home team, and a negative margin a win to the away team.