Stats Chat

Team Ratings for Week 10

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 51 matches played, 37 of which were correctly predicted, a success rate of 72.5%.
Here are the predictions for last week’s games.

Predictions for Week 10

Here are the predictions for Week 10. 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 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 93 matches played, 71 of which were correctly predicted, a success rate of 76.3%.
Here are the predictions for last week’s games.

Predictions for Round 15

Here are the predictions for Round 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 13

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 70 matches played, 35 of which were correctly predicted, a success rate of 50%.
Here are the predictions for last week’s games.

Predictions for Round 13

Here are the predictions for Round 13. 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.

According to a poll published in the Washington Post, a substantial majority of Americans think it is never justified for citizens to take violent action against the government. Given the US reverence for George Washington and others who fought in the Revolutionary War, this seems a bit strange. It’s hard to interpret what any particular percentage would mean.

What’s important about the poll is that the percentage is down compared to previous polls with the same question. It’s hard to interpret the level of agreement, but it seems pretty reasonable that a decrease indicates more willingness to consider violence against the government as an option that might come into play in the foreseeable future.  Or, at least, it would be if the polling approach hadn’t also changed, from phone to online, complicating any interpretation of changes.

Similarly, when the poll finds 30% of people claim to think there is solid evidence of widespread electoral fraud in 2020, it’s a bit hard to tell what that really corresponds to — how much is actual belief and how much is going along with a party line.  The fact that it’s about the same percentage as a year ago is more informative, as is the fact that it’s higher than similar questions about past elections.

Asking the same questions over time is a much better way to pick up changes than asking people if their opinion has changed. As a strategy, it can conflict with asking the best question, and that’s an ongoing tension in public opinion research and official statistics.

(The rugby prediction posts, while popular, are most interesting before the games actually happen: predicting the past is relatively easy)

First, the posts, regardless of year of writing, with most 2021 hits

1.  What’s a Group 1 Carcinogen? (2013) Points out that the IARC classification is not about severity or danger but about the types and amounts of evidence. Sunlight is a Group 1 Carcinogen, so are alcohol and plutonium.
2. A post about a Lotto strategy that doesn’t work(2012), as an argument about the usefulness of abstract theory. See also, the martingale optional stopping theorem
3. A climate change post about graphs that shouldn’t have a zero on the y-axis(2015)
4. From October 2020, but relevant to the news again in March this year, on crime rates in the Cuba/Courtenay area of Wellington and denominators
5. Actually from July this year, one of the StatsChat Dialogues: Q: Did you see that learning maths can affect your brain? A: Well, yes. There wouldn’t be much point otherwise

And the top 2021-vintage posts

1. Number 5 from the previous list
2. From October, on interpreting vaccination percentages
3. From April, why there’s so much fuss about very rare adverse reactions to vaccines (the AZ blood clots)
4. From October, why population structure matters to epidemic control, aka, why we need to vaccinate every subgroup. Has pictures!
5. From June, how a cap-and-trade system for (a subset of) emissions messes up our intuition about other climate interventions.

These are WordPress page views: their relationship to actual readership is complicated; keep in a cool, dry place away from children; may contain nuts.

A gentleman who is Not New Zealand’s Favourite DJ has tested positive for Omicron on his 9th day in NZ, after prior negative tests.  It seems surprising that a positive test could take so long — one theory is that it’s the sort of sporadic positive you can get for a while after recovery.  On the other hand, it’s worth thinking about why it’s surprising.  New Zealand keeps seeing strange Covid occurrences: long incubation period, transmission from very brief contact, and so on. Why us? It’s us because no-one else would be able to tell.

The normal assumption if a London DJ tests positive for Omicron on December 25 is that they got it in London a few days earlier. In this example, ‘a few days earlier’ means Waiheke Island and however he got there from MIQ;  in contrast to almost everywhere else in the world, Omicron isn’t circulating in Auckland.  The week before that he was in MIQ, so the next conclusion is that he got it there; unfortunate but not unprecedented. Without genome sequencing we’d stop there, but his viral genome doesn’t match any of the three he could potentially have picked up in MIQ.  We’re now down to weird possibilities, and the least weird is that he was carrying it all the time. But if he was almost anywhere else in the world, we wouldn’t even be starting to think about the weird possibilities.

It’s fairly easy to estimate the low end of the time-to-positive-test distribution: someone goes to a party; a few days later there are twenty cases; you do the maths. To get the low end you need some cases where you’re sure they couldn’t have been infected before a specific exposure, because they weren’t exposed before then. At the start of an outbreak that’s fairly easy. To get the high end of the distribution you need some cases where you’re sure they couldn’t have been infected after a specific exposure. That’s a much less common scenario, so the data aren’t as good.

Team Ratings for Week 9

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 49 matches played, 36 of which were correctly predicted, a success rate of 73.5%.
Here are the predictions for last week’s games.

Predictions for Week 9

Here are the predictions for Week 9. 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 14

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 87 matches played, 66 of which were correctly predicted, a success rate of 75.9%.
Here are the predictions for last week’s games.

Predictions for Round 14

Here are the predictions for Round 14. 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 12

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 65 matches played, 32 of which were correctly predicted, a success rate of 49.2%.
Here are the predictions for last week’s games.

Predictions for Round 12

Here are the predictions for Round 12. 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.

• Arithmetic fail by Bloomberg Australia: 126 cases over two days is not ‘more than double’ 62 cases in one day.
  
  They’ve since edited to “N.Z. Adds 126 Cases in 2 Days…New Zealand’s daily toll of new local infections has risen from the 62 reported on Dec. 24.”, which is at least arithmetically correct, since 2×62 is 124, and 126 is larger than 124.  Interestingly, the story now says “(Updates with state case numbers in third paragraph)” but doesn’t mention the correction to the maths

• The Washington Post reports on using convalescent plasma — antibodies from people who’ve recovered — to treat Covid. A new trial has positive results, but the story seriously underplays the previous trials with negative results. The story emphasizes that we’re short of treatments for Omicron so a new treatment would be more valuable, but that’s only true if it works, which is what’s in doubt
• Cruise ships are getting Covid outbreaks. Ok, yes, I’m shocked too.  More seriously, the problem is numbers. There were 3500 people on the ship. If each one is 99.95% sure to be Covid-free, that still comes to more than one expected case. At the sort of Covid prevalences the US has now, symptom screens and pre-departure tests aren’t good enough to get a high probability of a safe cruise.