June 27, 2017

NRL Predictions for Round 17

Team Ratings for Round 17

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.

Current Rating Rating at Season Start Difference
Storm 7.40 8.49 -1.10
Broncos 6.01 4.36 1.60
Cowboys 4.35 6.90 -2.60
Roosters 4.24 -1.17 5.40
Raiders 3.89 9.94 -6.10
Panthers 3.80 6.08 -2.30
Sea Eagles 3.65 -2.98 6.60
Sharks 1.80 5.84 -4.00
Warriors -1.53 -6.02 4.50
Dragons -2.40 -7.74 5.30
Eels -2.50 -0.81 -1.70
Rabbitohs -3.08 -1.82 -1.30
Bulldogs -3.84 -1.34 -2.50
Titans -4.16 -0.98 -3.20
Wests Tigers -8.61 -3.89 -4.70
Knights -11.10 -16.94 5.80

 

Performance So Far

So far there have been 118 matches played, 71 of which were correctly predicted, a success rate of 60.2%.
Here are the predictions for last week’s games.

Game Date Score Prediction Correct
1 Warriors vs. Bulldogs Jun 23 21 – 14 6.20 TRUE
2 Wests Tigers vs. Titans Jun 23 14 – 26 1.10 FALSE
3 Cowboys vs. Panthers Jun 24 14 – 12 4.50 TRUE
4 Raiders vs. Broncos Jun 24 20 – 30 3.50 FALSE
5 Roosters vs. Storm Jun 24 25 – 24 0.20 TRUE
6 Dragons vs. Knights Jun 25 32 – 28 13.80 TRUE
7 Sharks vs. Sea Eagles Jun 25 18 – 35 5.00 FALSE

 

Predictions for Round 17

Here are the predictions for Round 17. 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.

Game Date Winner Prediction
1 Eels vs. Bulldogs Jun 29 Eels 4.80
2 Titans vs. Dragons Jun 30 Titans 1.70
3 Broncos vs. Storm Jun 30 Broncos 2.10
4 Roosters vs. Sharks Jul 01 Roosters 5.90
5 Sea Eagles vs. Warriors Jul 01 Sea Eagles 5.20
6 Raiders vs. Cowboys Jul 01 Raiders 3.00
7 Knights vs. Wests Tigers Jul 02 Knights 1.00
8 Rabbitohs vs. Panthers Jul 02 Panthers -3.40

 

June 26, 2017

Briefly

  • A map of 1.3 billion taxi trips in New York, taking advantage of the underappreciated principle that there’s no point having more detail than the screen can display.  Also, GPS error naturally gives an attractive glowing effect that you’d usually have to add in afterwards
  • “In the summer of 2015, Alexandra Franco got a letter in the mail from a company she had never heard of called AcurianHealth. The letter, addressed to Franco personally, invited her to participate in a study of people with psoriasis, a condition that causes dry, itchy patches on the skin.”  A story about creepy data-mining, from Gizmodo.
  • From Scientific American, graphics showing daily, weekly, yearly patterns in number of births.
  • From the New York Times: a new drug for muscular dystrophy. It costs about US$1 million per year, and the FDA is not really convinced it has an effect
  • It’s time for the NZ Garden Bird Survey, which means it’s time for me to recommend their questions and answers page for its attention to principles of experimental design.
  • “Death when it comes will have no sheep”. Last week it was hamster names; this week it’s proverbs. Look, save yourself some effort and just go directly to Janelle Shane’s blog rather than waiting for each post to go viral.
  • In Science, probability is more certain than you think.” Chad Orzel

Stat of the Week Competition: June 24 – 30 2017

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 June 30 2017.
  • Statistics can be bad, exemplary or fascinating.
  • The statistic must be in the NZ media during the period of June 24 – 30 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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June 24, 2017

Cheese addiction: the book

I missed this a couple of weeks ago when it came out, but Stuff has a pretty good story on the ‘cheese addiction’ question.

As long-time readers will know, there’s been a persistent story circulating in the media claiming that a University of Michigan study found cheese was addictive because of substances called casomorphins.  The story is always unsourced (or sourced only to another copy), and the researchers at the University of Michigan have pointed out that this isn’t remotely like what their research found. The difference now is that Dr Neal Barnard, of the Physicians Committee for Responsible Medicine is fronting up. He’s written a book.

As the story on Stuff says (with added expert input), the cheese addiction claim doesn’t really stand up, but cheese is high in fat and there are things to not like about the dairy industry. And

While it’s not hard to pick holes in some of Barnard’s anti-cheese arguments, the book has good advice on what to eat instead

That could well be true but, as with paleo, you could find books that just give the recipes and leave out the scientifically-dubious propaganda.

June 21, 2017

NRL Predictions for Round 16

Team Ratings for Round 16

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.

Current Rating Rating at Season Start Difference
Storm 7.48 8.49 -1.00
Raiders 4.96 9.94 -5.00
Broncos 4.94 4.36 0.60
Cowboys 4.58 6.90 -2.30
Roosters 4.17 -1.17 5.30
Panthers 3.58 6.08 -2.50
Sharks 3.50 5.84 -2.30
Sea Eagles 1.95 -2.98 4.90
Warriors -1.60 -6.02 4.40
Dragons -1.61 -7.74 6.10
Eels -2.50 -0.81 -1.70
Rabbitohs -3.08 -1.82 -1.30
Bulldogs -3.76 -1.34 -2.40
Titans -5.19 -0.98 -4.20
Wests Tigers -7.57 -3.89 -3.70
Knights -11.88 -16.94 5.10

 

Performance So Far

So far there have been 111 matches played, 67 of which were correctly predicted, a success rate of 60.4%.
Here are the predictions for last week’s games.

Game Date Score Prediction Correct
1 Rabbitohs vs. Titans Jun 16 36 – 20 3.70 TRUE
2 Storm vs. Cowboys Jun 17 23 – 22 7.50 TRUE
3 Sharks vs. Wests Tigers Jun 17 24 – 22 16.90 TRUE
4 Eels vs. Dragons Jun 18 24 – 10 0.50 TRUE

 

Predictions for Round 16

Here are the predictions for Round 16. 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.

Game Date Winner Prediction
1 Warriors vs. Bulldogs Jun 23 Warriors 6.20
2 Wests Tigers vs. Titans Jun 23 Wests Tigers 1.10
3 Cowboys vs. Panthers Jun 24 Cowboys 4.50
4 Raiders vs. Broncos Jun 24 Raiders 3.50
5 Roosters vs. Storm Jun 24 Roosters 0.20
6 Dragons vs. Knights Jun 25 Dragons 13.80
7 Sharks vs. Sea Eagles Jun 25 Sharks 5.00

 

June 19, 2017

What’s brown and sticky?

Q: What’s brown and sticky?

A: A stick!

Q: What do you call a cow on a trampoline?

A: A milk shake!

Q: Where does chocolate milk come from?

A: Brown cows!

There’s a popular news story around claiming that 7% of Americans think chocolate milk comes from brown cows.

It’s not true.

That is, it’s probably not true that 7% of Americans think chocolate milk comes from brown cows.  If you try to trace the primary source, lots of stories point to Food & Wine, who point to the Innovation Center for U.S. Dairy, who point to Today.com, who point back to Food & Wine. Critically, none of the sources give the actual questions.  Was the question “Where does chocolate milk come from?” Was it “Lots of people say chocolate milk comes from brown cows, do you agree or disagree?” Was it “Does chocolate milk come from: (a) brown cows, (b) mutant sheep, (c) ordinary milk mixed with cocoa and sugar?” Was there a “Not sure” option?

This was clearly a question asked to get a marketing opportunity for carefully-selected facts about milk.  If the Innovation Center for US Dairy was interested in the factual question of what people believe about chocolate milk, they’d be providing more information about the survey and how they tried to distinguish actual believers from people who were just joking.

The Washington Post story does go into the more general issue of ignorance about food and agriculture: there’s apparently a lot of it about, especially among kids.  To some extent, though, this is what should happen. Via the NY Times

According to Agriculture Department estimates going back to 1910, however, the farm population peaked in 1916 at 32.5 million, or 32 percent of the population of 101.6 million.

It’s now down to 2%. Kids don’t pick up, say,  how cheese is made, from their day-to-day lives, and it’s not a top educational priority for schools.

The chocolate milk story, though, is bullshit: it looks like it’s being spread by people who don’t actually care whether the number is 7%.  And survey bullshit can be very sticky: a decade from now, we’ll probably find people citing this story as if it was evidence of something (other than contemporary news standards).

Stat of the Week Competition: June 17 – 23 2017

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 June 23 2017.
  • Statistics can be bad, exemplary or fascinating.
  • The statistic must be in the NZ media during the period of June 17 – 23 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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June 18, 2017

Unbiased anecdote is still anecdote

RadioNZ has a new “Healthy or Hoax” series looking at popular health claims. The first one, on coconut oil, is a good example both of what it does well, and of the difficulties in matching the claims and science.

The serious questions about coconut oil are about changes in blood fats and in insulin resistance when saturated fats replace various other components of the diet.  Replacing sugar and starch by  saturated fat is probably good; replacing, say,  monounsaturated fat by saturated fat probably isn’t. But in both cases the effects are small and are primarily on things you don’t notice, like your cholesterol level. That’s why there’s disagreement, because it’s actually hard to tell, given all the individual variability between people.

The superfood questions about coconut oil are about whether eating loads of it makes dramatic improvements in your health over a period of a few weeks.  There’s no reason to think it does, and the story quotes various people including Grant Schofield — who is at one end of the spectrum of respectable views on this subject — as saying so.

That’s all fine, but a big part of the story is about Kate Pereyra Garcia trying it for herself.  If the scientists — any subset of them — are right, a study on one person isn’t going to say anything helpful.  A one-person experience might disprove some of the extreme superfoodie claims, but no-one who believes those claims is likely to pay attention.

So, on one hand, the series looks like a great way to bring up the relatively boring evidence on a range of health topics. On the other hand, it’s reinforcing the concept of individual testimonials as a way of evaluating health effects.  If it was that easy to tell, we wouldn’t still be arguing about it.

Briefly

  • A simulation of measles spreading through communities with different vaccination levels.
  • Update on the prosecution of the former government statistician of Greece, Andreas Georgiou, apparently because the right numbers weren’t popular.
  • Blind testing suggests wine tasters do much better than chance, but nowhere near as well as they’d like you to think.
  • “It’s not that people don’t like Mexican food. The reason was that the system had learned the word “Mexican” from reading the Web.” On reducing the ethnic and gender biases of automated text analysis
  • Herald Insights visualisation of crime patterns in New Zealand. Yes, there’s a denominator problem; no, the obvious fixes wouldn’t help.

 

June 15, 2017

One poll is not enough

As Patrick Gower said recently about the new Newshub/Reid Research polls

“The interpretation of data by the media is crucial. You can have this methodology that we’re using and have it be bang on and perfect, but I could be too loose with the way I analyse and present that data, and all that hard work can be undone by that. So in the end, it comes down to me and the other people who present it.”

This evening, Newshub has the headline Poll: Labour crumbles, falling towards defeat. That’s based on a difference between two polls of 4.2% for Labour on its own, or 3.1% for a Labour/Greens alliance.

The poll has a ‘maximum margin of error’ of 3.1%, but that’s for support in this poll. For change between two polls, the maximum margin of error from the same assumptions is larger: 4.4%.

There’s pretty good evidence the decrease for Labour is likely to be real: at 25-30% support the random variation is smaller.  Even so, an uncertainty interval based on the usual optimistic assumptions about sampling goes from a decrease of 0.3% to a decrease of 8.1%.

The smaller change for the Greens/Labour alliance, this could easily just be the sort of thing that happens with polling. Or, it could be a real crumble. Or anything in between

Certainly, even a 3.1% decrease in support is potentially a big deal, and could be news. The problem is that a single standard NZ opinion poll isn’t up to the task of detecting it reliably. Whether it’s news or not is up to the judgement (or guesswork) of the media, and the demands of the audience.  Even that would be ok, if everyone admitted the extent to which the data just serve to dilute the reckons, rather than glossing over all the uncertainty.

If anyone wants less-exciting summaries, my current recommendation for an open, transparent, well-designed NZ poll aggregator is this by Peter Ellis.