April 27, 2015

Stat of the Week Competition: April 25 – May 1 2015

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…)

April 24, 2015

Graph of the week

Via @ian_sample on Twitter, a UK election ad

libdem

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:
dulwich

 

 

April 23, 2015

Genetic determinism: mosquito bite edition

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.

 

 

Don’t hold your breath

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.

 

April 22, 2015

Briefly

  • 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

NRL Predictions for Round 8

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.

Current Rating Rating at Season Start Difference
Roosters 8.52 9.09 -0.60
Rabbitohs 8.05 13.06 -5.00
Cowboys 7.76 9.52 -1.80
Storm 5.11 4.36 0.80
Broncos 4.63 4.03 0.60
Warriors 1.75 3.07 -1.30
Panthers 0.77 3.69 -2.90
Dragons 0.35 -1.74 2.10
Bulldogs 0.31 0.21 0.10
Knights -2.28 -0.28 -2.00
Sea Eagles -2.85 2.68 -5.50
Raiders -5.31 -7.09 1.80
Titans -5.36 -8.20 2.80
Sharks -5.85 -10.76 4.90
Eels -6.24 -7.19 0.90
Wests Tigers -8.00 -13.13 5.10

 

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.

Game Date Score Prediction Correct
1 Bulldogs vs. Sea Eagles Apr 17 28 – 16 5.20 TRUE
2 Dragons vs. Broncos Apr 17 12 – 10 -1.90 FALSE
3 Cowboys vs. Warriors Apr 18 28 – 24 11.00 TRUE
4 Storm vs. Roosters Apr 18 17 – 16 -0.70 FALSE
5 Titans vs. Panthers Apr 18 32 – 6 -7.60 FALSE
6 Knights vs. Eels Apr 19 22 – 28 9.10 FALSE
7 Wests Tigers vs. Raiders Apr 19 22 – 30 1.70 FALSE
8 Sharks vs. Rabbitohs Apr 20 18 – 10 -13.90 FALSE

 

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.

Game Date Winner Prediction
1 Bulldogs vs. Wests Tigers Apr 24 Bulldogs 11.30
2 Broncos vs. Eels Apr 25 Broncos 13.90
3 Knights vs. Cowboys Apr 25 Cowboys -7.00
4 Roosters vs. Dragons Apr 25 Roosters 11.20
5 Storm vs. Sea Eagles Apr 25 Storm 11.00
6 Warriors vs. Titans Apr 25 Warriors 11.10
7 Panthers vs. Sharks Apr 26 Panthers 9.60
8 Rabbitohs vs. Raiders Apr 26 Rabbitohs 16.40

 

Super 15 Predictions for Round 11

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.

Current Rating Rating at Season Start Difference
Crusaders 7.84 10.42 -2.60
Waratahs 7.50 10.00 -2.50
Chiefs 5.25 2.23 3.00
Hurricanes 5.18 2.89 2.30
Stormers 3.64 1.68 2.00
Bulls 3.43 2.88 0.60
Brumbies 3.22 2.20 1.00
Highlanders 1.02 -2.54 3.60
Blues 0.15 1.44 -1.30
Sharks -0.50 3.91 -4.40
Lions -3.19 -3.39 0.20
Force -5.75 -4.67 -1.10
Rebels -6.02 -9.53 3.50
Cheetahs -6.71 -5.55 -1.20
Reds -8.08 -4.98 -3.10

 

Performance So Far

So far there have been 66 matches played, 41 of which were correctly predicted, a success rate of 62.1%.

Here are the predictions for last week’s games.

Game Date Score Prediction Correct
1 Crusaders vs. Chiefs Apr 17 9 – 26 9.50 FALSE
2 Hurricanes vs. Waratahs Apr 18 24 – 29 3.30 FALSE
3 Highlanders vs. Blues Apr 18 30 – 24 4.60 TRUE
4 Brumbies vs. Rebels Apr 18 8 – 13 15.60 FALSE
5 Force vs. Stormers Apr 18 6 – 13 -4.40 TRUE
6 Sharks vs. Bulls Apr 18 10 – 17 1.10 FALSE
7 Cheetahs vs. Reds Apr 18 17 – 18 6.90 FALSE

 

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.

Game Date Winner Prediction
1 Chiefs vs. Force Apr 24 Chiefs 15.50
2 Brumbies vs. Highlanders Apr 24 Brumbies 6.70
3 Crusaders vs. Blues Apr 25 Crusaders 11.70
4 Waratahs vs. Rebels Apr 25 Waratahs 17.50
5 Lions vs. Cheetahs Apr 25 Lions 7.50
6 Stormers vs. Bulls Apr 25 Stormers 4.20
7 Reds vs. Hurricanes Apr 26 Hurricanes -8.80

 

April 20, 2015

Stat of the Week Competition: April 18 – 24 2015

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 April 24 2015.
  • Statistics can be bad, exemplary or fascinating.
  • The statistic must be in the NZ media during the period of April 18 – 24 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…)

April 15, 2015

Briefly

  • Good article in New York Times about why ‘survival rates’ aren’t the best way to assess progress in cancer. Same explanation that I’ve covered before several times: survival can improve when all you do is move diagnosis earlier without affecting disease or death at all
  • Whether state government subsidy of tuition in the US is increasing or decreasing seems like it should be an easy question. Not so much.
  • Comparing prices from different years without inflation adjustment is like comparing prices from different countries without currency conversion.  Any inflation adjustment is better than none, but if you’re interested in different ways it can be done there’s a fairly comprehensible review by the UK Statistics Authority
  • Headlines based on bogus polls are back. At Stuff, an implausible headline from a survey created to publicise a dating app and National Cheese Week. Celebrate National Library Week instead.

NRL Predictions for Round 7

Team Ratings for Round 7

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
Rabbitohs 9.55 13.06 -3.50
Roosters 8.65 9.09 -0.40
Cowboys 8.27 9.52 -1.30
Storm 4.98 4.36 0.60
Broncos 4.92 4.03 0.90
Panthers 3.02 3.69 -0.70
Warriors 1.24 3.07 -1.80
Dragons 0.06 -1.74 1.80
Bulldogs -0.19 0.21 -0.40
Knights -1.23 -0.28 -1.00
Sea Eagles -2.36 2.68 -5.00
Raiders -6.00 -7.09 1.10
Eels -7.29 -7.19 -0.10
Wests Tigers -7.31 -13.13 5.80
Sharks -7.35 -10.76 3.40
Titans -7.62 -8.20 0.60

 

Performance So Far

So far there have been 48 matches played, 25 of which were correctly predicted, a success rate of 52.1%.

Here are the predictions for last week’s games.

Game Date Score Prediction Correct
1 Broncos vs. Roosters Apr 10 22 – 18 -1.50 FALSE
2 Sharks vs. Knights Apr 10 22 – 6 -6.20 FALSE
3 Eels vs. Titans Apr 11 16 – 38 7.30 FALSE
4 Panthers vs. Sea Eagles Apr 11 22 – 12 8.10 TRUE
5 Warriors vs. Wests Tigers Apr 11 32 – 22 13.00 TRUE
6 Dragons vs. Bulldogs Apr 12 31 – 6 -0.20 FALSE
7 Raiders vs. Storm Apr 12 10 – 14 -8.70 TRUE
8 Rabbitohs vs. Cowboys Apr 13 12 – 30 7.80 FALSE

 

Predictions for Round 7

Here are the predictions for Round 7. 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 Bulldogs vs. Sea Eagles Apr 17 Bulldogs 5.20
2 Dragons vs. Broncos Apr 17 Broncos -1.90
3 Cowboys vs. Warriors Apr 18 Cowboys 11.00
4 Storm vs. Roosters Apr 18 Roosters -0.70
5 Titans vs. Panthers Apr 18 Panthers -7.60
6 Knights vs. Eels Apr 19 Knights 9.10
7 Wests Tigers vs. Raiders Apr 19 Wests Tigers 1.70
8 Sharks vs. Rabbitohs Apr 20 Rabbitohs -13.90