Posts from April 2015 (35)

From the Herald, under the headline “First-home buyers nab new home subsidies”

The AMP 360 First Home Buyer Affordability Report, published yesterday, shows housing remains “affordable” in all regions except Auckland and Queenstown.

The index tracked the lower-quartile (halfway between zero and the median) selling prices of houses and the median after-tax income of typical first-home buyers (a working couple both aged 25 to 29).

The lower quartile is not “halfway between zero and the median”. The lower quartile is the price that 25% of sales are below and 75% are above.

What’s more, the interpretation is obviously wrong. If you take the first Google link, at interest.co.nz, there’s a table by region, and it lists the lower quartile price for Auckland metro as $587000 and Auckland City as $681000. The Herald reports the median price often enough that they must know it isn’t over a million dollars.

While I’m complaining: the data table at interest.co.nz is in a state of sin. It’s not actually a data table; it’s a picture of a data table, a GIF image.

Team Ratings for Round 9

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 64 matches played, 30 of which were correctly predicted, a success rate of 46.9%.

Here are the predictions for last week’s games.

Predictions for Round 9

Here are the predictions for Round 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 12

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 73 matches played, 48 of which were correctly predicted, a success rate of 65.8%.

Here are the predictions for last week’s games.

Predictions for Round 12

Here are the predictions for Round 12. 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.

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 May 1 2015.
• Statistics can be bad, exemplary or fascinating.
• The statistic must be in the NZ media during the period of April 25 – May 1 2015 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.

(more…)

If you’d like to comment on or debate any of this week’s Stat of the Week nominations, please do so below!

Via @ian_sample on Twitter, a UK election ad

The basic approach has been traditional with the Liberal Party since before they merged with the Social Democratic Party; the accuracy has been, let’s say, variable. In this example, the 19-point difference between Labour and Liberal Democrats is shown as larger smaller than the 5-point difference between Liberal Democrats and Conservatives.

Here’s what those numbers really look like:

Q: Did you see that being bitten by mosquitoes is genetic?

A: What? Being outside without mosquito repellent, especially in the evening, is genetic now?

Q: No.

A: Living in places with lots little pools of standing water in the summer is genetic?

Q: No

A: Having wire mesh screens on your windows is genetic?

Q: Ok, yes, very droll. No, “Scientists have found that the chance of being bitten by a mosquito is written in the genes and some people are just more likely to be attacked no matter how much insect repellent they slap on.” What repellent did they use? DEET or one of those lemon things?

A: You mean this paper in PLoS One. They didn’t use any repellent.

Q: So they don’t really know that the usual repellents don’t work for some people because of genetics?

A: No. They didn’t look at that at all.

Q: Should I pretend to be shocked?

A: Don’t bother for now.

Q: Ok, who got bitten by the mosquitoes? You’re not going to tell me it was mice again, are you?

A: No, no mice, but also no bites. The researchers took smell samples from volunteers’ hands, and measured which samples the mosquitoes flew towards?

Q: How did they choose the people?

A: The comparisons were all within sets of female twins.

Q: Not really a representative population sample, was it?

A: It’s a reasonable approach for testing if there’s a genetic component to something: identical twins should be more similar than non-identical twins.

Q: And if it was completely genetic, identical twins would be identical, right?

A: Yes.

Q: So when they say “the mosquitoes would bite none, or both of the identical twins, but the results were mixed for the non-identical twins” that means it was completely genetic?

A:  No, the implication doesn’t work backwards that way. And also that’s a pretty serious exaggeration of what they found.

Q: But at least they did find a genetic component? Some people make a natural repellent?

A: There’s pretty good evidence of a genetic component, even a fairly big one. The article makes it clear that they don’t know whether some people make a repellent or whether other people make an attractant: “It is not known whether the differences between MZ and DZ twins is due to the presence or absence of attractive or repellent chemicals,”

Q: That seems pretty unambiguous, but it isn’t what the newspaper says.

A: No, it isn’t.

Q: Should I pretend to be shocked now?

A: I’d wait and get it over with all at once.

Q: The newspaper has a link to a related story. Should we read that?

A: Sure. Why not?

Q: It says “most of this research uses only one mosquito species. Switch to another species and the results are likely to be different.” Huh. I didn’t know that. Which species did the twin research use?

A: Aedes aegypti, a tropical mosquito (originally from Africa) that spreads yellow fever and dengue.

Q: Is Aedes aegypti common in New Zealand?

A: No, it could live in Northland but the biosecurity folks have stopped it invading so far.

Q: How about in the UK, where the news story came from initially?

A: No, the UK is too cold.

Q: So it’s not really relevant to mosquito bites for their readers?

A: It’s still important as a global health issue, but no, not all that relevant from a mundane viewpoint of actual day-to-day utility.

Q: Ok, is now the time to pretend to be shocked?

A: If it makes you feel better, sure.

The story at the Herald (from the Telegraph) starts off dramatically, then walks its claims back, but not back far enough.

First off, the dramatic claim:

Asthma could be cured within five years after scientists discovered what causes the condition and how to switch it off.

Then the description of what the researchers actually did: ‘identified which cells cause the airways to narrow when triggered by irritants like pollution.’ That’s less dramatic; it’s also not true. The researchers looked at the same cells everyone else looks at. What they did was show that a molecule on the surface of these cells (“calcium-sensing receptor”) appears to be central to the triggering.

The other main selling point:

Crucially, drugs already exist which can deactivate the cells. They are known as calcilytics and are used to treat people with osteoporosis.

In fact, they aren’t used to treat people with osteoporosis. As the research paper says, they “were initially developed as anti-osteoporotic drugs and reached phase 2 clinical trials for this purpose”. That is, they didn’t work. They might work for asthma, but it’s not like finding a new use for an actually-marketed drug — especially as the drugs would have to be inhaled, something that hasn’t been studied in humans at all. If everything goes right, it might be possible to get the safety and effectiveness studies done and the drug approved in five years, but that’s pretty optimistic.

Also, the drugs are promising, but not as promising as the story says:

But when calcilytic drugs are inhaled, it deactivates the cells and stops all symptoms.

Most of the research was either in isolated cells (which don’t have symptoms) or in non-asthmatic mice. One experiment, in asthmatic mice, showed a reduction in airway resistance with the drugs, but not down to the level in non-asthmatic mice.  And airway resistance isn’t the same as symptoms. And these are mice.

A comment from Asthma UK raises another point that hasn’t appeared so far

“Five per cent of people with asthma don’t respond to current treatments so research breakthroughs could be life changing for hundreds of thousands of people. If this research proves successful we may be just a few years away from a new treatment for asthma”

Inhaled steroids for asthma are already pretty effective. While they aren’t enough for everyone, a more common problem is the hassle of using the inhaler twice a day every day when you’re healthy, to prevent relatively rare asthma attacks.  The new drugs will likely have the same problem  — it’s a treatment, not a cure — and their real potential isn’t for everyone with asthma, but for the relatively small subset where current treatments don’t work.

• Large numbers are dehumanising, so should big data worry us? From the Guardian

• On the other hand, statistics and a real-time display  on the use of emoji have got to be humanising, right? (via @mlle_elle)

• AirBnB’s data blog

• From the BBC: The illusion of control and how it makes us feel better. That’s part of the benefit of real-time transit prediction: knowing how long you have to wait makes you feel more in control, as long as the system is good enough not to shatter the illusion.

• Social networks to visualise relationships between allegedly-independent landlords

• A systematic, data-based comparison of Shanghai xiao long bao vendors
  
  

Team Ratings for Round 8

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 56 matches played, 27 of which were correctly predicted, a success rate of 48.2%.

Here are the predictions for last week’s games.

Predictions for Round 8

Here are the predictions for Round 8. 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.