Posts filed under General (453)

April 25, 2014

Briefly

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Sham vs controlled studies: Thomas Lumley’s latest Listener column

How can a sham medical procedure provide huge benefits? And why do we still do them in a world of randomised, blinded trials? Thomas Lumley explores the issue in his latest New Zealand Listener column. Click here.

April 24, 2014

Quarter of a million meth labs?

3 News saysTests find meth traces in 40pc of houses“.

Now, this is only rentals, but according to the Census there are 563000 rental dwellings in the country, so 40% would be nearly quarter of a million.  If you’re marketing the test as detecting meth labs, this statistic implies either a hugely unrepresentative sample or a test with a high false-positive rate.

In fact it’s probably both. The sample is dwellings where the landlord bought a test from the company MethSolutions, so you’d hope they were higher-risk than average, and the

[MethSolutions] director Miles Stratford told 3 News the results varied from low-level meth use to high-end meth manufacturing.

“Some of the instances that we’ve found are people using industrial cleaner inside of properties. We’ve had instances where there have been low-grade plastics fires that have produced a whole bunch of volatile gases into the air that have been picked up.”

 So the test is picking up both traces of use and unrelated activity in additional to actual manufacture of methamphetamine. The company website doesn’t give any information, as far as I can tell, about either the false positive or false negative rate of the tests — they mention Ministry of Health guidelines, but these guidelines are for remediation of known meth labs, not for screening.

And if you’re thinking about using this service you should, of course, read their terms and conditions, which disclaim any guarantees of any level of accuracy, disclose that the service is subsidised by referrals of positive tests to clean-up companies

Where an indicative test is undertaken on behalf of or for the benefit of the owner of a property and that owner or their insurer chooses not to utilise MethSolutions dedicated service providers in quantifying and/or decontaminating and/or reinstating a property, an additional charge of $200 + GST will be due and payable for each of these services that is not utilised but which is required in order to ensure a property is fit to be lived in.

and have other interesting section headlines such as “MethSolutions Is not an Environmental Testing or Security Company” and “No Guarantees on Cost of Sampling.”

NRL Predictions for Round 8

Team Ratings for Round 8

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
Roosters 7.58 12.35 -4.80
Bulldogs 6.81 2.46 4.30
Rabbitohs 5.83 5.82 0.00
Sea Eagles 5.67 9.10 -3.40
Cowboys 3.17 6.01 -2.80
Storm 1.71 7.64 -5.90
Broncos 1.12 -4.69 5.80
Titans 0.17 1.45 -1.30
Knights -0.10 5.23 -5.30
Sharks -2.77 2.32 -5.10
Panthers -2.84 -2.48 -0.40
Wests Tigers -3.86 -11.26 7.40
Dragons -4.82 -7.57 2.80
Raiders -4.93 -8.99 4.10
Warriors -5.06 -0.72 -4.30
Eels -9.47 -18.45 9.00

 

Performance So Far

So far there have been 56 matches played, 29 of which were correctly predicted, a success rate of 51.8%.

Here are the predictions for last week’s games.

Game Date Score Prediction Correct
1 Rabbitohs vs. Bulldogs Apr 18 14 – 15 4.70 FALSE
2 Knights vs. Broncos Apr 18 6 – 32 9.20 FALSE
3 Sea Eagles vs. Cowboys Apr 18 26 – 21 7.60 TRUE
4 Dragons vs. Warriors Apr 19 20 – 10 3.40 TRUE
5 Sharks vs. Roosters Apr 19 18 – 24 -5.80 TRUE
6 Raiders vs. Storm Apr 20 24 – 22 -3.20 FALSE
7 Eels vs. Wests Tigers Apr 21 18 – 21 -0.60 TRUE
8 Panthers vs. Titans Apr 21 14 – 12 1.30 TRUE

 

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 Dragons vs. Roosters Apr 25 Roosters -7.90
2 Storm vs. Warriors Apr 25 Storm 11.30
3 Broncos vs. Rabbitohs Apr 25 Rabbitohs -0.20
4 Sharks vs. Panthers Apr 26 Sharks 4.60
5 Cowboys vs. Eels Apr 26 Cowboys 17.10
6 Bulldogs vs. Knights Apr 26 Bulldogs 11.40
7 Sea Eagles vs. Raiders Apr 27 Sea Eagles 15.10
8 Wests Tigers vs. Titans Apr 27 Wests Tigers 0.50

 

Super 15 Predictions for Round 11

Team Ratings for Round 11

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
Sharks 7.28 4.57 2.70
Crusaders 7.24 8.80 -1.60
Chiefs 4.07 4.38 -0.30
Brumbies 4.06 4.12 -0.10
Waratahs 3.37 1.67 1.70
Bulls 2.68 4.87 -2.20
Hurricanes 1.41 -1.44 2.80
Stormers 1.09 4.38 -3.30
Reds -0.84 0.58 -1.40
Blues -2.23 -1.92 -0.30
Force -2.85 -5.37 2.50
Highlanders -3.83 -4.48 0.70
Cheetahs -4.05 0.12 -4.20
Rebels -4.77 -6.36 1.60
Lions -5.65 -6.93 1.30

 

Performance So Far

So far there have been 61 matches played, 39 of which were correctly predicted, a success rate of 63.9%.

Here are the predictions for last week’s games.

Game Date Score Prediction Correct
1 Hurricanes vs. Blues Apr 18 39 – 20 4.30 TRUE
2 Rebels vs. Force Apr 18 22 – 16 -0.20 FALSE
3 Chiefs vs. Crusaders Apr 19 17 – 18 -0.60 TRUE
4 Waratahs vs. Bulls Apr 19 19 – 12 4.30 TRUE
5 Sharks vs. Cheetahs Apr 19 19 – 8 14.30 TRUE
6 Stormers vs. Lions Apr 19 18 – 3 8.40 TRUE

 

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 Blues vs. Waratahs Apr 25 Waratahs -1.60
2 Brumbies vs. Chiefs Apr 25 Brumbies 4.00
3 Sharks vs. Highlanders Apr 25 Sharks 15.10
4 Hurricanes vs. Reds Apr 26 Hurricanes 6.30
5 Force vs. Bulls Apr 26 Bulls -1.50
6 Cheetahs vs. Stormers Apr 26 Stormers -2.60

 

April 21, 2014

How much does a wedding cost?

From The Wireless, because that’s where I happened to notice it, not because they did anything wrong

But the average wedding costs about $30,000 – equivalent to a down payment on a house, another comparable goal for a couple in their twenties.

That is the stylised number: you can find it in Stuff and the Herald and lots of other places. But what does it mean? Could it really be true that a typical couple spends about half their annual income on a marriage?

A One News story last year said

Nicky Luis, owner of Lavish Events in Auckland, said while there were no official statistics on the average cost in New Zealand, perceptions within the industry put the figure at $30,000.

That is, people working in the lavish-weddings industry perceive there to be lots of lavish weddings and think it’s normal to spend a lot of money getting married.

Even when the number is supposedly based on surveys there are problems, as Will Oremus wrote last year at Slate

The first problem with the figure is what statisticians call selection bias. One of the most extensive surveys, and perhaps the most widely cited, is the “Real Weddings Study” conducted each year by TheKnot.com and WeddingChannel.com. (It’s the sole source for the Reuters and CNN Money stories, among others.) They survey some 20,000 brides per annum, an impressive figure. But all of them are drawn from the sites’ own online membership, surely a more gung-ho group than the brides who don’t sign up for wedding websites, let alone those who lack regular Internet access.

To make matters worse, the summary quoted from the surveys is the mean, but the way the figure is used, a median would be more appropriate. Oremus extracts the information that  the median is about 2/3 of the mean in those surveys, so we’re getting a 50% increase on top of the selection bias.

When you’re thinking about weddings you’ve been to, there is a different sort of bias. Expensive weddings tend to have more guests, so the average wedding you get invited to is larger than the average wedding you might have got invited to but didn’t.

April 19, 2014

Seeing no evil

The Herald story “Uni cheats: hundreds punished” is a pretty good example of using actual data to combat the ‘false balance’ problem in journalism.  The story notes the huge variation in official proceedings for cheating between NZ universities — nearly half the cases are at Waikato — and rightly highlights it as “suggesting differences in what institutions consider cheating, and how they target and record it.”

As the story doesn’t point out, with 540 cases out of more than 400000 tertiary students it’s pretty clear cheating is underreported everywhere. That’s hardly surprising, given the costs and benefits to staff for following it up. If it wasn’t for the irrational rage cheating arouses in academics, it would be perfectly safe.

 

There’s nothing to it

From the Herald, in a good article about the Australian report on homeopathy

Auckland homeopath Suzanne Hansen said the treatments could not be measured in the same way medical treatments were.

“When you research it against a medical paradigm it will fail because you treat in a completely different way.”

This is probably true, but it’s a major concession that should be noted for the record.

The`medical paradigm’ of randomised controlled trials doesn’t need treatment to be the same for each person, it doesn’t need the benefits to be the same for each person, it doesn’t need the biological mechanism to be known or even plausible. All they need is that you can identify some group of people and a way of measuring success so that getting your treatment is better on average for your chosen group of people with your chosen way of defining ‘better’.  This isn’t just about homeopathy —  the whole field of personalised genomic medicine is based on individualising treatment, and this doesn’t introduce any difficulties for the medical paradigm.

If an intervention can’t beat fake pills that do nothing, on its choice of patient group and outcome measurement, it will fail when you `research it against a medical paradigm.’  If you’re fine with that, you should be fine with not using any advertising terms that suggest the intervention has non-placebo benefits.

April 18, 2014

Briefly

Cannabis and Radio Yerevan

Radio Yerevan jokes were a thing in the Soviet Union days

The Armenian Radio was asked: “Is it true that in Moscow, Mercedes cars are being given to citizens?”

The Armenian Radio answers: “Yes, but it is not Moscow but Leningrad, not Mercedes but Ladas, and not given to but stolen from.” 

From the Herald, yesterday

People who had only used cannabis once or twice a week for a matter of months were found to have changes in the brain that govern emotion, motivation and addiction.

Here’s the research paper, which you won’t be able to access, so I’ll summarisse

Firstly, no-one in the study was found to have ‘changes’ in the brain: the participants got only one brain scan, so the research didn’t even look at changes. It found differences between cannabis users and non-users. There’s nothing even slightly surprising about the possibility that people who end up as regular users of an illegal drug might have started off with brain differences.

There were 20 cannabis users in the study, who smoked an average of 11 joints per week, and had been smoking cannabis for an average of six years. Here’s the data for one of their findings, on ‘gray matter density in the nucleus accumbens’

potbrain

 

The dots at zero are the controls, the other dots are the cannabis users. There certainly aren’t many who use cannabis only once or twice per week. It’s hard to tell whether there’s really anyone who has only used cannabis for a few months,  because the research paper only reports the mean and standard deviation for duration of use.

So, the main point of the story in the paragraph quoted above is completely unsupported by the research.  This one isn’t entirely the fault of the media, since the researchers were pushing hard to exactly this sort of unsupported claim into the papers.  Still, you might have hoped someone they talked to would have matched up the claims to the research..