Stats Chat

• 92% of people think they’re better than average at complying with Covid-19 rules (UK study).  It could be that people who comply with Covid rules are also more likely to respond to surveys, but it also wouldn’t be surprising if most people just think they’re better than average.
• A (flashing) map of lighthouses
• “Did 4 per cent of Americans really drink bleach last year?” — a good piece at the NZ$ Herald, from the Harvard Business Review. Spoiler: no, probably not: it’s the sort of claim that surveys are bad at supporting.
• “Every recorded battle in history” on a map (click to embiggen).
  
  “recorded” means recorded by Wikipedia. The European bias is pretty clear, but note that it even misses battles in the Waikato and Taranaki wars where British soldiers were awarded the Victoria Cross, so the Wikipedia completeness bias is more complicated than just ‘European soldiers’.

Q: Did you see dogs are better than lateral flow tests for detecting Covid?

A: No

Q: The Guardian says: Dogs can better detect Covid in humans than lateral flow tests, finds study. With 97% accuracy!!

A: That’s the detection rate in people with Covid. The detection rate of Covid in people without Covid is 9%, which is a lot higher than you’d like.

Q: Where did they find the people?

A: It was people turning up to a testing centre in Paris, though since 109 out of 335 had Covid, it can’t really have been representative. The test positivity rate in France as a whole is only 4.5% at the moment and peaked at 15.9%

Q: Is 335 people enough?

A: Potentially, though the study initially planned to get 2000 people

Q: The story says lateral flow tests correctly identify on average 72% of people infected with the virus who have symptoms, and 58% who do not. That sounds really bad. Why does anyone use them?

A:  There’s a lot of variability between tests: some of them are better.  Also, they have much, much lower false positive rates than the dogs — around half a percent.  Since there’s a tradeoff between conservative (giving false negatives) and being sensitive (giving false positives), you can’t just compare the sensitivity of two tests that have a ten-fold difference in false positive rate.

Q: Still dogs would be quicker, and you could just use the real test in people the dogs picked out

A: That has potential, but dogs don’t scale all that well. You need to train and test each dog; they can’t just be mass-produced, boxed up, and mailed around the country.  And dogs aren’t that much quicker — this isn’t walk-past sniffing like the beagles looking for smuggled food at Auckland airport; you need to stick a pad in your armpit for a couple of minutes.

Q: How much of the spin is from the research paper and how much is coming from the newspaper.

A: The researchers are reported in the French source: “Ces résultats confirment scientifiquement la capacité des chiens à détecter une signature olfactive de la Covid-19“, souligne l’AP-HP, précisant que cette étude, pas encore publiée dans une revue médicale, est “la première de ce type réalisée au niveau international“.

Q: J’ai pas de clue que that means

A:  “These results scientifically confirm the ability of dogs to detect an olfactory signature of Covid-19 “, emphasise [the hospital], specifying that this study, not yet published in a medical journal, is ” the first of this type carried out in international level “.

Q: So it’s not just the Guardian

A: No.

Team Ratings for Round 20

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 107 matches played, 69 of which were correctly predicted, a success rate of 64.5%.
Here are the predictions for last week’s games.

Predictions for Round 20

Here are the predictions for Round 20. 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 Postponed Games

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 166 matches played, 113 of which were correctly predicted, a success rate of 68.1%.
Here are the predictions for last week’s games.

Predictions for Postponed Games

Here are the predictions for Postponed Games. 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 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 48 matches played, 35 of which were correctly predicted, a success rate of 72.9%.
Here are the predictions for last week’s games.

Predictions for Week 14

Here are the predictions for Week 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 4

These predictions come with a caveat. I have done them mainly with a view to updating my ratings for the Pro 14 teams and in particular the South African Super Rugby teams. Having done them, I thought I might as well publish them from now on. The initial ratings are derived from the end of the Pro 14 and Super Rugby Unlocked competitions. Even though there are really two separate competitions it is convenient to lump them together because that is how the fixtures and results are available on the internet.

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 24 matches played, 13 of which were correctly predicted, a success rate of 54.2%.
Here are the predictions for last week’s games.

Predictions for Round 4

Here are the predictions for Round 4. 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 11

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 80 matches played, 56 of which were correctly predicted, a success rate of 70%.
Here are the predictions for last week’s games.

Predictions for Round 11

Here are the predictions for Round 11. 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 24

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 159 matches played, 107 of which were correctly predicted, a success rate of 67.3%.
Here are the predictions for last week’s games.

Predictions for Round 24

Here are the predictions for Round 24. 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 Postponed Games

Another unusual week. There are two midweek games and the teams involved will be playing later in the week as well. I will give predictions for the weekend games after obtaining the results for the two midweek games.

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 157 matches played, 106 of which were correctly predicted, a success rate of 67.5%.
Here are the predictions for last week’s games.

Predictions for Postponed Games

Here are the predictions for Postponed Games. 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 13

Just a note concerning the ratings this week. There have been no games between Australian and New Zealand sides since early in 2020. The ratings below started off from the ratings after the last of those games and have been updated based on games in Super Rugby Aotearoa and Super Rugby Australia in 2020 and 2021. Caution is needed about the ratings for this next series of Super Rugby games because of this ratings history. I chose not to shrink the previous ratings before the start of this series of games which is something I usually do to a minor extent between seasons.

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 43 matches played, 30 of which were correctly predicted, a success rate of 69.8%.
Here are the predictions for last week’s games.

Predictions for Week 13

Here are the predictions for Week 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.