Posts from September 2013 (69)

The Herald had a story on Tuesday about a UN survey of men in nine areas in Asia/Oceania asking about rape and violence against women.  The story is pretty good, and actually has links to the articles in the medical journal Lancet.

Because of the wide publicity and the large scale of the survey I think it’s worth nailing down some of the details to make it harder to dismiss.  (more…)

Even so often, one of the NZ lottery jackpots gets to be unusually large and we see an increasing stream of search engine hits from people looking for ways to win.

Via @mapcaptenor, here’s an analysis of the USA’s Powerball lottery, with the conclusion

The one sentence takeaway: no matter how big the jackpot gets, you should only buy Powerball tickets for their entertainment value.

In fact, an economics argument can get you this conclusion much more easily. All the facts you have about the lottery are available to pretty much anyone in the country, as is the opportunity to buy tickets. Unless you think you are one of the top handful of smartest investors in New Zealand, you should assume that other people will draw the same conclusion as you about whether it’s worth buying tickets. If you think it’s worth buying, so will quite a lot of other people, and collectively you’ll buy up enough tickets to ensure that the expected benefit falls to nearly zero.

The Herald, like many other news sources worldwide, has picked up on a paper in the Proceedings of the National Academy of Sciences. Like the other glamorous top science journals, PNAS publishes some top-level science, and also some that is perhaps not quite up to the standard.

The story says that men with smaller testicles make better fathers, based on a fairly weak correlation in a relatively small sample of new fathers. As Dr Isis points out, this sample only included 9 dads who did more childcare than the mothers.

If you look at the paper (which you can’t, unless you have a subscription), you find that there was a moderately strong relationship between testosterone levels in the blood and the ‘parenting quality’ questionnaire. When the researchers compared men with similar levels of testosterone and similar working hours, there was no correlation between testicle size and parenting, but if testosterone and hours at work were ignored there was fairly weak evidence of a correlation between testicle size and parenting.  (The researchers presented their evidence using p-values, with p=0.08 , not up to usual standards. I think it would be unconvincing with other ways of measuring evidence as well)

The Discussion section of the paper starts out

which is, apparently unintentionally,  a pretty damning criticism.

Oh, the post title? Anyone old and British should be able to explain it

Statistics New Zealand is marking 120 years of women’s suffrage with a nice little infograph (click to enlarge).

The graphics are a recent development, and long may they continue (and that the print media and teachers make the most of them). The last SNZ graphic I saw marked the birth of a certain baby called George, and looked at a range of facts and figures to do with child-rearing in New Zealand.

If you’re in Palmerston Nth, next Tuesday 17th, James Curran is talking as part of the Royal Society’s 10×10 series of maths presentations around the country

Advances in science have allowed forensic practitioners to recover and quantify evidence from crime scenes in more ways than ever before. As a consequence, judges, lawyers, and juries struggle to decide or understand what the value of scientific evidence might be, and how it impacts on the case at hand. This talk will look at how statistics is being used to aid in the legal process.

And if you’re in Auckland on October 1, I’m presenting at Nerdnite again, (6:30 for 7pm, Nectar bar, above the Kingslander)

“The game of rock, paper, scissors was known in Asia millennia ago. At about the time of Captain Cook, a French political scientist discovered that it isn’t always possible to construct an ordering by considering things two at a time.  In the 1970s a statistician showed how to cheat at dice using this idea. The implications for experiments with a treatment group and a control group are still underappreciated.”

One of our early Stat-of-the-Week awards was for this graph from The Standard

Among the problems is that the graph is cumulative, so it unavoidably goes up.  It’s a good choice if you want the impression of a relentless increase regardless of the data; not so good if you’re trying to inform.

Tim Cook, of Apple, did something similar with iPhone sales at the product release yesterday

David Yanofsky, at Quartz, overlays the quarterly sales reports

It’s clear that quarterly sales have been declining recently, although it’s also clear that each new iPhone leads to a sales surge.  The quarterly reports actually tell you something about the sales pattern; the cumulative reports really don’t.

In the same way, although these two graphs of StatsChat page views contain the same information, the first one lets you see  patterns over time, such as the start of the rugby-prediction season, and the times I’m away. Cumulative charts are usually less useful and often misleading, whether deliberately or not.

A live visualisation of  locations for a light-rail system in San Francisco. The diagonal lines show the timetable schedule, so you can see speed as well as lateness

Something like this for Auckland buses would be neat, but, sadly, the bus location data are secret.

I have now been able to assemble the data for predicting the ITM Cup. The success figures stated below are what would have been achieved had I started predicting in Round 1. The parameters for this season’s predictions were chosen without considering any results from this year and the method is purely algorithmic once the parameters have been chosen.

Team Ratings for Round 5

Here are the team ratings prior to Round 5, along with the ratings at the start of the season. I have created a brief description of the method I use for predicting rugby games. Go to my Department home page to see this.

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, 24 of which were correctly predicted, a success rate of 80%.

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 Round 6

Here are the team ratings prior to Round 6, along with the ratings at the start of the season. I have created a brief description of the method I use for predicting rugby games. Go to my Department home page to see this.

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 15 matches played, 7 of which were correctly predicted, a success rate of 46.7%.

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.

Team Ratings for Finals Week 1

Here are the team ratings prior to this week’s games, along with the ratings at the start of the season. I have created a brief description of the method I use for predicting rugby games. Go to my Department home page to see this.

Performance So Far

So far there have been 192 matches played, 116 of which were correctly predicted, a success rate of 60.42%.

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.