Posts from December 2011 (32)

This week we’ve been talking with Sam Mulgrew, a statistical reporter for Media7, about some of the statistics in the media highlights from this year.

If you’re interested, tune in to see what’s covered tonight at 9:05pm on TVNZ7 or watch it when it’s available on YouTube.

The Early Breast Cancer Trialists Collaborative Group has published a combined analysis of over 400 trials of breast cancer treatments, in 400,000 women.  They were trying to ‘personalise’ treatment

Moderate differences in efficacy between adjuvant chemotherapy regimens for breast cancer are plausible, and could affect treatment choices. We sought any such differences.

And what did they find?

 In all meta-analyses involving taxane-based or anthracycline-based regimens, proportional risk reductions were little affected by age, nodal status, tumour diameter or differentiation (moderate or poor; few were well differentiated), oestrogen receptor status, or tamoxifen use.

That is, based on all the characteristics they had available, there really wasn’t any way to predict which treatment would work best for which subset of the women.

Now, we know that some more-recent treatments do only work on a subset of tumours. In breast cancer there is Herceptin, which targets one particular tumour growth mechanism and only works on tumours that grow that way, and there are similar specific inhibitors for some other cancer subtypes.  It’s still striking how difficult it is to detect  any useful variation between people in treatment effectiveness, a finding that’s also be true in other areas of medicine.  So-called ‘personalized medicine’ may one day be possible, but it’s a long way off and current technologies don’t give us any way to get there.

That got your attention didn’t it? The article Are You Inhaling Secondhand Coke? certainly got my attention when I read it on Slashdot but more in the kind of “correlation being misinterpreted as causation” way.

To be fair to the scientists in the study, they do actually say this, but the journalist who wrote it up did not find it necessary to include that information until the reader is about three quarters of the way through the article.

Somebody should nominate this for Stat of the Week.

You may remember the story about Auckland air pollution being worse than Tokyo, due to data entry errors by the World Health Organization.  The Science Media Centre has put out a new graphic showing actual air pollution levels around the country and around the world. [They also have the right spelling and location for Dunedin]

Levels are moderately high in the south of the South Island, due largely to the use of wood fires for heating.  It’s worth noting that woodsmoke seems to have different health effects from the car and truck exhaust and factory emissions that dominate the fine-particle air pollution in other places with dirty air.  Seattle, where I used to live, had a similar problem with wood smoke, and there has been a lot of study of the health effects. It looks as though wood smoke has harmful effects on the lungs, especially in triggering asthma attacks, but that it doesn’t have as much effect on the heart. Studies in Seattle find no relationship between heart disease and PM10, in contrast to cities where coal or diesel emissions are the main pollutant and associations are found consistently.

Windblown dust also seems to be less harmful: at the Biometric Society conference in Australia a couple of weeks ago there was a presentation on the 2009 Sydney dust storm, which raised PM10 levels to an amazing 15,000 micrograms per cubic meter.  Even at these massive doses the researchers saw no increase in hospital admissions for cardiovascular disease, and a only modest 15% increase for asthma admissions and 25% increase for asthma hospital visits.

Thanks to Sammy and Steve for their nominations last week.

Sammy highlights a very common misconception – except that those who think it are not going to be loyal viewers of StatsChat!

Steve’s graph does suppress zero, but the data is there to think about, and the number of injuries reported has – for whatever reason – almost doubled in 5 years.

Congratulations to Sammy for being this week’s Stat of the Week winner!

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 December 23 2011.
• Statistics can be bad, exemplary or fascinating.
• The statistic must be in the NZ media during the period of December 17-23 2011 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.

The fine print:

• Judging will be conducted by the blog moderator in liaison with staff at the Department of Statistics, The University of Auckland.
• The judges’ decision will be final.
• The judges can decide not to award a prize if they do not believe a suitable statistic has been posted in the preceeding week.
• Only the first nomination of any individual example of a statistic used in the NZ media will qualify for the competition.
• Employees (other than student employees) of the Statistics department at the University of Auckland are not eligible to win.
• The person posting the winning entry will receive a $20 iTunes voucher.
• The blog moderator will contact the winner via their notified email address and advise the details of the $20 iTunes voucher to that same email address.
• The competition will commence Monday 8 August 2011 and continue until cancellation is notified on the blog.

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

The Age (yes, I’m just back from the West Island) has an article on the annual cancer statistics report from the Victorian Cancer Council.  Survival from diagnosis is up for many cancers, and that’s the headline, but in only some of these diseases is there a reduction in the death rate.

The problem is that survival from diagnosis measures the interval between two time points: diagnosis, and death.  You can increase your survival time by dying later, which is a Good Thing, or by being diagnosed earlier and dying at the same time, which many people would consider bad.

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The Herald, along with many other sources, reports on US employment: “Far fewer Americans are seeking unemployment benefits than just three months ago – a sign that layoffs are falling sharply.”  By the standards of the US recession, this qualifies as good news, though the bar has to be set pretty low.  A fall in layoffs, on its own, just means that things aren’t getting worse as quickly, and the time limit on eligibility means that an increasing number  of  people are falling off the end of benefits.

Actual unemployment figures are also positive, but a bit less so.  The unemployment rate fell by 0.5%, but half of that was people who stopped looking for work.  Total employment is up, by an estimated 280,000 people, which is promising [the figure of 120,000 given by the Herald is ‘total non-farm payroll employment’].

The real problem in interpreting these numbers is that the increase in employment and the decrease in applications for benefits are both much smaller than the seasonal adjustment factor (as Brad DeLong points out).  Without seasonal adjustment, the total increase in jobs was only 80,000, more than three times smaller.

The basic idea of seasonal adjustment is uncontroversial  — there’s lots of variation over the year in employment in retail, construction, and  farming, and the education system releases a wave of new labour force members at the end of each academic year.  However, in a recession that’s unprecedented since good-quality records began, it’s hard to predict the seasonal variations exactly right.   A small error in the seasonal adjustment could wipe out the apparent gains entirely. And a while seasonally-adjusted employment is the right indicator for the economy as a whole, you can’t afford much Christmas cheer with only a seasonally-adjusted new income.

Andrew Gelman and Kaiser Fung have an article in American Scientist

As the authors of statistics-themed books for general audiences, we can attest that Levitt and Dubner’s success is not easily attained. And as teachers of statistics, we recognize the challenge of creating interest in the subject without resorting to clichéd examples such as baseball averages, movie grosses and political polls. The other side of this challenge, though, is presenting ideas in interesting ways without oversimplifying them or misleading readers. We and others have noted a discouraging tendency in the Freakonomics body of work to present speculative or even erroneous claims with an air of certainty. Considering such problems yields useful lessons for those who wish to popularize statistical ideas.