Stats Chat

Team Ratings for the Preliminary Finals

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 198 matches played, 119 of which were correctly predicted, a success rate of 60.1%.
Here are the predictions for last week’s games.

Predictions for the Preliminary Finals

Here are the predictions for the Preliminary Finals. 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 38 matches played, 24 of which were correctly predicted, a success rate of 63.2%.
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.

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 30 matches played, 20 of which were correctly predicted, a success rate of 66.7%.
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.

There’s a new Herald story with the lead

Artificial intelligence (AI) can identify Alzheimer’s disease 10 years before doctors can discover the symptoms, according to new research.

The story doesn’t link (even to the Daily Mail). Before we get to that, regular StatsChat readers will have some idea of what to expect.

Early diagnosis for Alzheimer’s is potentially useful when designing clinical trials for new treatments, and eventually will be useful for early treatment (when we get treatments that work).  But not yet.  It’s also not as much of a novelty as the story suggests. Candidate tests for early diagnosis are appearing all over the place (here’s seven of them).

Second, you’d expect that the accuracy of the test and its degree of foresight to have been exaggerated — and the story confirms this.

Following the training, the AI was then asked to process brains from 148 subjects – 52 were healthy, 48 had Alzheimer’s disease and 48 had mild cognitive impairment (MCI) but were known to have developed Alzheimer’s disease two and a half to nine years later.

That is, the early diagnosis wasn’t of people without symptoms, it was of people whose symptoms had led to a diagnosis but didn’t amount to dementia

The Herald doesn’t link, but Google finds a story at New Scientist, and they do link. The link is to the arXiv preprint server. That’s unusual: normally this sort of story is either complete vapour or is based on an article in a research journal.  This one is neither: it’s a real scientific report, but one that hasn’t yet been published — it’s probably undergoing peer review at the moment.

Anyway, the preprint is enough to look up the accuracy of the test. The sensitivity was high: nearly all Alzheimer’s cases and cases of Mild Cognitive Impairement were picked up. The specificity was terrible: more than 1/4 of people tested would receive a false positive diagnosis.

It’s possible that this test can be re-tuned into a genuinely useful clinical tool. As published, though, it isn’t even close.

Q: Did you see icecream for breakfast may improve mental performance?

A: Pigs may fly

Q: But it’s a STUDY

A: That’s actually one of the questions left unresolved.

Q: Just follow the link. The International Business Times links to their source.

A: That link is to a Japanese news site. And it’s 404.

Q: Already? The tweet was just from this weekend.

A: The story is from November last year.

Q: But there’s a professor! Isn’t he real? Can’t you look at his publications.

A: Yes, he’s real. And he has publications. And they aren’t about icecream for breakfast.

Q: Back to the icecream. It could still be true, even if the data aren’t published, right?

A: Sure. In fact there’s a fair chance that, compared to no breakfast, icecream could improve mental performance.

Q: The comparison was to not eating anything?

A: It was compared to a glass of cold water.

Q: So, what does this tell us?

A: 2017 must be a slow news year.

Each week, we would like to invite readers of Stats Chat to submit nominations for our Stat of the Week competition and be in with the chance to win an iTunes voucher.

Here’s how it works:

• Anyone may add a comment on this post to nominate their Stat of the Week candidate before midday Friday September 22 2017.
• Statistics can be bad, exemplary or fascinating.
• The statistic must be in the NZ media during the period of September 16 – 22 2017 inclusive.
• Quote the statistic, when and where it was published and tell us why it should be our Stat of the Week.

Next Monday at midday we’ll announce the winner of this week’s Stat of the Week competition, and start a new one.

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From last week in the Herald: 73.6 per cent of landlords plan rent rises if Labour wins. It’s been a while since I noticed a bogus-poll headline, but they keep coming back.

This time there are two independent reasons this number is meaningless.  First, it’s a self-selected survey — a bogus poll.  You can think of self-selected surveys as a type of petition: they don’t tell you anything useful about the people who didn’t respond, so the results are only interesting if the absolute number responding in a particular category is surprisingly high.  In this case, it’s 73.6% of 816 landlords. According to an OIA request in 2015,  there are more than 120,000 landlords in NZ, so we’re looking at a ‘yes’ response from less than half a percent of them.

Second, there’s an important distinction in polling questions to worry about.  If a nice pollster calls you up one evening and asks who you’re voting for, there’s no particular reason to say anything other than the truth.  The truth is the strongest possible signal of your political affiliation.  If a survey asks “will you raise rents if Labour gets in and raises costs?”,  it’s fairly natural to say “yes” as a sign that you don’t support Labour, whether it’s true or not. There’s no cost to saying “yes”, but if you’re currently setting rents at what you think is the right level, there is a cost to raising them.

Those of you who do arithmetic compulsively will have noticed another, more minor, problem with the headline.  There is no number of votes out of 816 that rounds correctly to 73.6%:  600/816 is 73.52941%, ie, 73.5% and 601/816 is 73.65196, ie, 73.7%.  And, of course, headlining the results of any poll, even a good one, to the nearest tenth of a percentage point is silly.

There are competing explanations out there about what happens to votes for a party that doesn’t reach the 5%/1 electorate threshold.  This post is about why I don’t like one of them.

People will say (such as on NZ Morning Report this morning) that your votes are reallocated to other parties.  In some voting systems, such as the STV we use for local government elections, reallocating votes is a thing. Your voting paper literally (or virtually) starts off in one party’s pile and is moved to a different party’s pile.

That’s not what happens with the party votes for Parliament.  If the Greens don’t make 5%, party votes for the Greens are not used in allocating List seats.  It’s exactly as if those voters hadn’t cast a party vote, which I think is a simple enough explanation to use.

Now, in the vast majority of cases the result will be the same as if the votes had been reallocated in proportion — unless something weird like a tie happens at some stage in the counting — but one of the explanations is what happens and the other one isn’t.

If you think the two explanations convey the same meaning, you shouldn’t object to using the one that’s actually correct. And if you think they convey different meanings, you definitely shouldn’t object to using the one that’s actually correct.

Team Ratings for Finals 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 196 matches played, 118 of which were correctly predicted, a success rate of 60.2%.
Here are the predictions for last week’s games.

Predictions for Finals Week 2

Here are the predictions for Finals 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 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 30 matches played, 19 of which were correctly predicted, a success rate of 63.3%.
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.