October 13, 2014

Context from everyday units

From @JohnDonoghue64 on Twitter


From the Guardian, a few years ago

Perhaps, as with metric and imperial measurements, such comparisons should be given convenient abbreviations: SoWs (size of Wales), SoBs (size of Belgium), OSPs (Olympic swimming pools), DDBs (buses) and so on. Thus the Kruger national park in South Africa measures 1 SoW (Daily Telegraph), as do Lesotho (London Evening Standard) and Israel (Times), whereas Lake Nzerakera in Tanzania is 2 SoBs (Observer).

At times the most carefully calibrated calculations can go awry. So we learn that Helmand province in Afghanistan is “four times the size of Wales” (Daily Telegraph, 2 December 2009) only to find a few weeks later that it has apparently shrunk to “the size of Wales” (Daily Telegraph, 29 January 2010).

For the benefit of NZ readers, a badger appears to weigh about the same as three female North Island brown kiwi, two typical merino fleeces, or half a case of Malborough sav blanc. That should help you get a grasp on the size of the Lindisfarne Gospels.

Herald data blog starts

The Herald’s Data Editor, Harkanwal Singh,  announces the online site’s new ‘Data Blog’, with the first new post being a map of NZ internet affordability created by Jonathan Brewer.

This has got to be a Good Thing for data literacy in the local media.

Stat of the Week Winner: October 4 – 10 2014

Thanks for your nominations last week for our Stat of the Week competition!

This week, we’ve chosen the following to be our winner:

“‘Rates of participants brushing their teeth rose from 53 per cent to 73 per cent during the trial.’

This story got quite a bit of coverage, the stat actually relates to an increase in the number of people texting and saying they had brushed their teeth (far from the same thing).

The Herald got the context correct in their coverage:

This still seems to just be evidence that people will say anything when nagged enough.”

Congratulations Ben Moore!

Stat of the Week Competition: October 11 – 17 2014

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 October 17 2014.
  • Statistics can be bad, exemplary or fascinating.
  • The statistic must be in the NZ media during the period of October 11 – 17 2014 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.


October 12, 2014

Unofficially over arithmetic

From the Herald (from the Washington Post), under the headline “Teens are officially over Facebook” (yes, officially)

Now, a pretty dramatic new report out from Piper Jaffray – an investment bank with a sizable research arm – rules that the kids are over Facebook once and for all, having fled Mark Zuckerberg’s parent-flooded shores for the more forgiving embraces of Twitter and Instagram.

This is based on a survey by Piper Jaffray, of 7200 people aged 13-19, (in the US, though the Herald doesn’t say that).

It looks as though US teens are leaving Facebook, but they sure aren’t flocking to Twitter, or, really, to Instagram. If you go to a story that gives the numbers, you see that reported Facebook use has fallen 27 percentage points. Instagram has risen only 7 percentage points, and Twitter has fallen by 4.


So, where are they going? They aren’t giving up on social media entirely — although “None” category wasn’t asked the first time around, it’s only 8 percent in the second survey.  It’s possible that teens are cutting down on the number of social media networks they use, but it seems more likely that the question was badly designed. Even I can think of at least one major site that isn’t on the list, Snapchat, which globalwebindex thinks is used by 42% of US internet-connected 16-19 year olds.

Incidentally: those little blue letters that look like they should be a link? They aren’t on the Herald site either, and on the Washington Post site they link to a message that basically says “no, not for you.”

October 10, 2014


  • Something strange happened to this month’s unemployment data in Australia: Guardian, ABC News, interview with Rob Hyndman (who knows from time series)
  • “Ferguson’s 3,287 new registrants (in two months) is more than recorded by any township in St. Louis County in any midterm election since 2002.” Or not. A number that seems really extreme may just be wrong.
  • When there’s a lot of variation, it can be a mistake to make statements about “typical” attitudes: Andrew Gelman
October 9, 2014

…and to divide the light from the darkness

Q: There’s a story that charging your phone in your bedroom make you fat.

A: Yes, there is.

Q: Why?

A: Because it looked like a good headline.

Q: No, why does it make you fat?

A: Melatonin. The theory is that any light at night time makes your body not produce enough melatonin and that this is bad.

Q: How much more did people who charged their phones in their bedroom end up weighing?

A: There weren’t any people involved.

Q: Ok, so they had mice with cellphones in their bedrooms?

A: Rats. And not cellphones.

Q: Some other light source of a similar brightness?

A: No.

Q: What, then?

A: They put melatonin in the rats’ drinking water.

Q: So that should make them lose weight. Did it?

A: Not that they reported.

Q: Can you work with me here?

A: They measured the conversion of fat under the rats’ skin from ‘white’ to ‘brown‘, which is theoretically relevant to energy use and perhaps to diabetes and heart disease. It’s interesting research. (abstract)

Q: So it could be relevant, but doesn’t the generalisation seems a bit indirect?

A: Yes, “a bit.”

Q: Do international patterns of cellphone use match patterns of obesity?

A: Not really, but maybe in East Asia they use different chargers or something.

Q: Is the LED on a charger really enough to make a difference?

A: That’s what the story lead implies, but the second paragraph talks about research involving phone screens, laptops, artificial lighting, and street lights, so I’m guessing there’s a bit of a bait and switch going on.

Q: Couldn’t it be enough? I mean, in nature, it would be completely dark at night, like they say.

A: Only up to a point. There was another relevant story today, too.


October 8, 2014

Communicating the obvious (to you)

From the Herald

People’s coffee-drinking habits are linked to their genes, scientists say.

A large-scale study, which analysed 20,000 regular coffee drinkers of European and African American ancestry, identified six new genetic variants associated with habitual coffee drinking.

What the story (and the press information) doesn’t say is how small the effects are: among regular coffee drinkers, each of these variants predicted a difference in average consumption of one or two cups per month. (research paper, paywalled)

The  researchers would think it’s obvious that the effects are going to be tiny, so it makes sense that they wouldn’t point this out explicitly. The journalists and publicists wouldn’t know, but there’s no reason they would think to ask.

What are CEOs paid; what should they be paid?

From Harvard Business Review, reporting on recent research

Using data from the International Social Survey Programme (ISSP) from December 2012, in which respondents were asked to both “estimate how much a chairman of a national company (CEO), a cabinet minister in a national government, and an unskilled factory worker actually earn” and how much each person should earn, the researchers calculated the median ratios for the full sample and for 40 countries separately.

The graph:



The radial graph exaggerates the differences, but they are already huge. Respondents dramatically underestimated what CEOs are actually paid, and still thought it was too much.  Here’s a barchart of the blue and grey data (the red data seems to only be available in the graph). Ordering by ideal pay ratio (rather than alphabetically) helps with the nearly-invisible blue bars: it’s interesting that Australia has the highest ideal ratio.


The findings are a contrast to foreign aid budgets, where the desired level of expenditure is less than the estimated level, but more than the actual level.  On the other hand, it’s less clear exactly what the implications are in the CEO case.


October 7, 2014

Currie Cup Predictions for Round 10

Team Ratings for Round 10

The basic method is described on my Department home page. I have made some changes to the methodology this year, including shrinking the ratings between seasons.

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
Western Province 7.02 3.43 3.60
Lions 4.39 0.07 4.30
Sharks 3.35 5.09 -1.70
Blue Bulls -0.18 -0.74 0.60
Cheetahs -1.89 0.33 -2.20
Pumas -7.97 -10.00 2.00
Griquas -8.90 -7.49 -1.40
Kings -15.13 -10.00 -5.10


Performance So Far

So far there have been 36 matches played, 27 of which were correctly predicted, a success rate of 75%.

Here are the predictions for last week’s games.

Game Date Score Prediction Correct
1 Sharks vs. Lions Oct 03 26 – 23 4.10 TRUE
2 Pumas vs. Blue Bulls Oct 03 6 – 37 0.80 FALSE
3 Cheetahs vs. Western Province Oct 04 29 – 34 -3.70 TRUE
4 Griquas vs. Kings Oct 04 45 – 25 10.00 TRUE


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.

Game Date Winner Prediction
1 Kings vs. Pumas Oct 10 Pumas -2.20
2 Lions vs. Cheetahs Oct 11 Lions 11.30
3 Western Province vs. Sharks Oct 11 Western Province 8.70
4 Blue Bulls vs. Griquas Oct 11 Blue Bulls 13.70