Posts from September 2019 (19)

Team Ratings for Week 1

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.

Predictions for Week 1

Here are the predictions for Week 1. 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.

Publication Schedule

I aim to publish RWC predictions on a schedule which ensures that team ratings have been calculated using all prior results. With 5 teams per pool and 4 pools, only 8 games can be played without the necessity for a team to play twice and that is how the pool games schedule appears to have been arranged. I thus intend to publish new predictions after each group of 8 games. There may be some variations in when I publish because I am currently on a cycling holiday in Europe.

For the NRL and Mitre 10 Cup predictions, I aim to publish on a Tuesday each week as usual.

We haven’t had one of these for a while, but there’s some dodgy-looking extrapolation going on in the Keep New Zealand Beautiful litter audit. The audit itself is a good idea: measure litter in a detailed and reproducible way, so you can compare amounts now to amounts in the future and see whether things are getting greener and cleaner.  And I don’t have any problems with how they conducted the survey.

But.  The report (PDF) says (p18)

10,269,090,000 LITTERED CIGARETTE BUTTS polluting our ecosystem

and the Herald story says

Despite drops in smoking rates, discarded cigarette butts remained a big headache: some 10,269,090,000 were picked up, or 2,142 for every person in the country.

There weren’t 10 billion cigarette butts picked up. That would take a while.  There were 39 cigarette butts picked up per 1000 square metres of land surveyed. With 10,000 477,000 square metres surveyed [update: I was confused by Table 2 in the report, which says 10,000 but is just illustrating the calculation (that’s the Table 2 on p25, not one of the others)], that comes to 390 18600.  The detailed breakdowns in the report are fine, but there are also these extrapolations, where the amount of litter per 1000 square metres is scaled up by the number of 1000 square metre patches it would take to cover the whole country — about 260,000,000.

And, similarly, from the Herald quoting KNZB chief executive Heather Sanderson

“Extrapolated, that means 265,324,848 litres of illegal dumping – enough to fill 2,123 rail carriages, which if you stack them on top of each other, would be as high as 151 Sky Towers.”

is obtained by finding just under 1 litre (or 0.001 cubic metres) per 1000 square metres in the survey, and scaling up to the whole country. (Also, those imaginary rail carriages are being stacked end on end, which is probably not good for them)

Scaling up like this is how survey statistics works, but only if the sites you survey are an equal-probability random sample of the area  The report doesn’t say they were, and it seems pretty unlikely, because it’s quite hard to get to a lot of randomly chosen bits of New Zealand, and these places  — whether they’re up inaccessible mountains or in the middle of a big dairy farm  — will tend to have less litter.

[Update: it’s obvious not an equal-probability sample of NZ; it could be some sort of stratified sample of the types of areas they were focusing on]

[Update, 13 September: Keep NZ Beautiful has modified the report to take out the dodgy extrapolations.  Congratulations.  The Herald hasn’t modified their story, though.]

Team Ratings for Finals Week 1

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 192 matches played, 123 of which were correctly predicted, a success rate of 64.1%.
Here are the predictions for last week’s games.

Predictions for Finals Week 1

Here are the predictions for Finals Week 1. 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 6

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 35 matches played, 23 of which were correctly predicted, a success rate of 65.7%.
Here are the predictions for last week’s games.

Predictions for Round 6

Here are the predictions for Round 6. 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.

• An actual evaluation: ‘Kentucky lawmakers thought requiring that judges consult an algorithm when deciding whether to hold a defendant in jail before trial would make the state’s justice system cheaper and fairer by setting more people free. That’s not how it turned out.’ Ars Technica
• From the CEO of Palantir, in the Washington Post “Companies and innovators in Silicon Valley have immense, almost monopolistic power. Many have lucrative contracts with the government. But under scrutiny from employees and activists, they are being pressured to avoid controversy by picking and choosing which contracts to accept and which to abandon. “ He thinks that’s a bad thing.
• The winners of MonoCarto 2019 (formerly known as the Monochrome Mapping Competition)
• We’re about to have another bit of democracy.  To prepare, places.figure.nz gives you information about your local government areas. The Spinoff’s “Policy Local” is asking all local government candidates a set of questions and putting the answers in an app
• Those Hurricane Maps Don’t Mean What You Think They Mean.  Albert Cairo in the NYT.

Kim Hill on Radio NZ had a long interview with David Spiegelhalter, who is Professor of the Public Understanding of Risk, at Cambridge.   He has a new book, “The Art of Statistics: Learning from Data”

Team Ratings for Round 25

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 184 matches played, 118 of which were correctly predicted, a success rate of 64.1%.
Here are the predictions for last week’s games.

Predictions for Round 25

Here are the predictions for Round 25. 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 28 matches played, 19 of which were correctly predicted, a success rate of 67.9%.
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.

Team Ratings for the Currie Cup Final

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.

Note that Cheetahs2 refers to the Cheetahs team when there is a Pro14 match. The assumption is that the team playing in the Pro14 is the top team and the Currie Cup team is essentially a second team. Possibly there will be no such clashes this year

Performance So Far

So far there have been 23 matches played, 14 of which were correctly predicted, a success rate of 60.9%.
Here are the predictions for last week’s games.

Predictions for the Currie Cup Final

Here are the predictions for the Currie Cup Final. 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.