Stats Chat

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 50 matches played, 32 of which were correctly predicted, a success rate of 64%.
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 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 98 matches played, 76 of which were correctly predicted, a success rate of 77.6%.
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.

Ok, this is a bit late, but I didn’t see the poll (in a physical Sunday Star-Times) until this week.  An established Australian polling firm, Freshwater Strategy, have been doing polls here, too.  Stuff reports that the poll (also, at the Post)

…reveals 37% of New Zealand voters have seriously considered emigrating to Australia in the past 12 months.

By comparison, of Australian voters, only 8% have considered moving to New Zealand, including just 1% who have spent time looking into it.

If you don’t think too carefully, that gives the impression of a giant sucking sound and the lights going out in New Zealand.  Australia is a lot larger than New Zealand, though.  If 8% of people in Australia moved to New Zealand and 37% of people in New Zealand moved to Australia, the population of New Zealand would go up, not down.  The total populations are about 5 million and about 27 million. Of those, about 3.6 million are enrolled to vote in NZ and nearly 18 million enrolled to vote in Australia, so 37% of NZ voters is 1.3 million and 8% of Oz voters is 1.44 million.

Another useful comparison number is that the largest ever number of people migrating out of NZ to all destinations, not just Australia, over any 12 months is about 130,000, a tenth of the ‘seriously considered’ number. A lot of people (apparently) seriously consider a lot of things they don’t end up doing.

The other important aspect of the story is the estimates quoted for small subpopulations.  Overall, the poll claims a maximum margin of error of about  3 percentage points. That’s for the population as a whole. Proportions are given for different age groups, including 18-34 year olds, people earning more than $150,000, and voters for Te Pāti Māori.  We aren’t told the uncertainty in these numbers, but it’s obviously higher.  About 1/3 of adults are 18-34, about 5% earn over $150k (IRD spreadsheet), and about 3% voted for Te Pāti Māori.  The maximum margin of error for subpopulations this big would be 5, 13, and 17 percentage points respectively, assuming equal sampling.   You can’t easily learn much about wealthy people or Pāti Māori voters just by contacting random people throughout the country — and the assumption that you can make your sample representative by reweighting gets increasingly dodgy.

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 69 matches played, 51 of which were correctly predicted, a success rate of 73.9%.
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 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 91 matches played, 71 of which were correctly predicted, a success rate of 78%.
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 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 45 matches played, 29 of which were correctly predicted, a success rate of 64.4%.
Here are the predictions for last week’s games.

Predictions for Round 10

Here are the predictions for Round 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.

If you’ve been paying attention to the food scare news, you will have heard that black plastic spatulas are EVIL and then that they are probably ok.  Predicted exposures to brominated flame retardants were close to the ‘reference level’ because of a simple decimal-place error and there’s now a ten-fold safety margin. The summary by Joel Schwarcz at McGill University in Canada is good; as he notes, there is no actual need for spatulas to be flame-retardant and while the level of fire retardants doesn’t look dangerous, the target level should be roughly zero.

There are two additional points I want to make. First, units.  The original scare paper quoted the ‘oral reference dose’ as 7000 nanograms per kg per day. The EPA document that it cited said 0.007 mg per kilogram per day. These are terrible units.  The SI system gives us names every three orders of magnitude precisely so we don’t have to do this sort of thing and can say 7 micrograms per kilogram per day. It’s a lot easier to work with numbers like this.

Second, what does the reference dose mean?  If you look at the relevant EPA document you will see that the 7 micrograms per kilogram per day comes by taking a reference dose for non-cancer effects in mice and multiplying dividing it by 10 because humans might be more sensitive than mice, and a further 10 because you might be more sensitive than the typical human and a further 3 because long-term exposure might matter more than short-term exposure.  And, on reading further, that the dose for mice was the highest dose tested in that experiment and did not show any adverse effects.  So, the 7 micrograms per kilogram per day reference dose is 300 times the highest dose they even tested for mice.  Some other experiments did find adverse effects in rats, but at doses nearly a thousand times higher: 6 milligrams per kg per day.

Taking all this together you can see the fuzziness in the calculations. There’s now a ten-fold margin of safety between a generously estimated dose and a reference dose — which is not a danger dose, but one that should have no effect.  On top of that, there’s an unknown (and possibly large) safety factor because of the choice of doses in the mouse safety experiments.  The basic problem is that you can’t tell accurately what doses will cause harm in humans without causing harm in humans; some sort of extrapolation is unavoidable in safety assessment.

The Isle of Arran, as I’m sure you all know, is on the west side of Scotland  Being an island, it has somewhat limited means of access: Caledonian MacBrayne run two ferries from the mainland.  These ferries are being replaced with allegedly better ferries. However, the BBC headline said ‘Green’ ferry emits more CO2 than old diesel ship

In reply, “Ferries procurement agency CMAL, which owns the ship, said the comparison was “inaccurate” as Glen Sannox is a larger vessel.” 

While New Zealand is very attached to per capita representations of everything, sometimes they aren’t helpful.  The new ship is bigger. Precisely for that reason, it would emit more CO2 if run on the same fuel as the old ship.  The plan is actually to run the ship on liquified fossil gas imported from Qatar and trucked up from the south of England. This would reduce the CO2 emissions, but would produce methane emissions that pretty much compensate for the reduction — and the UK follows mainstream science in recognising that methane actually matters.

In some settings, such as comparing Auckland’s double-decker buses to traditional buses, it’s important to take account of the fact that they’re bigger and so you don’t need as many of them to carry all your passengers.  But when you’re talking about a ferry route with two ships there isn’t the same room for per capita savings to pay off the larger per-ship emissions.   If you run the same number of trips with bigger ships you’ll get more emissions. And if you can carry more cars on the bigger ferries that’s not really going to reduce emissions, either.

Team Ratings for Week 9

This is the promised update after the Dragons v Cardiff Rugby game.

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 62 matches played, 46 of which were correctly predicted, a success rate of 74.2%.
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 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 84 matches played, 66 of which were correctly predicted, a success rate of 78.6%.
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.