Posts filed under Risk (130)

August 15, 2014

Cancer statistics done right

I’ve mentioned a number of times that statistics on cancer survival are often unreliable for the conclusion people want to draw, and that you need to look at cancer mortality.  Today’s story in Stuff is about Otago research that does it right:

The report found for 11-year timeframe, cancer-specific death rates decreased in both countries and cancer mortality fell in both countries. But there was no change in the difference between the death rates New Zealand and Australia, which remained remained 10 per cent higher in New Zealand.

That is, they didn’t look at survival after diagnosis, they looked at the rate of deaths. They also looked at the rate of cancer diagnoses

“The higher mortality from all cancers combined cannot be attributed to higher incidence rates, and this suggests that overall patient survival is lower in New Zealand,” Skegg said.

That’s not quite as solid a conclusion — it’s conceivable that New Zealand really has higher incidence, but Australia compensates by over-diagnosing tumours that wouldn’t ever cause a problem — but it would be a stretch to have that happen over all types of cancer combined, as they observed.

 

August 14, 2014

Breast cancer risk and exercise

Stuff has a story from the LA Times about exercise and breast cancer risk.  There’s a new research paper based on a large French population study, where women who ended up having a breast cancer diagnosis were less likely to have exercised regularly for the past five year period.  This is just observational correlation, and although it’s a big study, with 2000 breast cancer cases in over 50000 women, the evidence is not all that strong (the uncertainty range around the 10% risk reduction given in the paper goes from an 18% reduction down to a 1% reduction).  Given that,  I’m a bit unhappy with the strength of the language in the story:

For women past childbearing age, a new study finds that a modest amount of exercise — four hours a week of walking or more intensive physical activity such as cycling for just two hours a week — drives down breast cancer risk by roughly 10 per cent.

There’s a more dramatically wrong numerical issue towards the end of the story, though:

The medications tamoxifen and raloxifene can also drive down the risk of breast cancer in those at higher than average risk. They come with side effects such as an increased risk of deep-vein thrombosis or pulmonary embolism, and their powers of risk reduction are actually pretty modest: If 1000 women took either tamoxifen or raloxifene for five years, eight breast cancers would be prevented.

By comparison, regular physical activity is powerful.

Using relative risk reduction for the (potential) benefits of exercise and absolute risk reduction for the benefits of the drugs is misleading. Using the breast cancer risk assessment tool from the National Cancer Institute, the five-year breast cancer risk for a typical 60 year old is perhaps 2%. That agrees with the study’s 2000 cases in 52000 women followed for at least nine years.  If 1000 women with that level of risk took up regular exercise for five years, and if the benefits were real,  two breast cancers would be prevented.

Exercise is much less powerful than the drugs, but it’s cheap, doesn’t require a doctor’s prescription, and the side-effects on other diseases are beneficial, not harmful.

August 7, 2014

New breast cancer gene

The Herald has a pretty good story about a gene, PALB2, where there are mutations that cause a substantially raised risk of breast cancer.  It’s not as novel as the story implies (the first sentence of the abstract is “Germline loss-of-function mutations in PALB2 are known to confer a predisposition to breast cancer.”), but the quantified increase in risk is new and potentially a useful thing to know.

Genetic testing for BRCA mutations is funded in NZ for people with a sufficiently strong family history, but the policy is to test one of the affected relatives first. This new gene demonstrates why.

If you had a high-risk family history of breast cancer, and tested negative for BRCA1 and BRCA2 mutations, you might assume you had missed out on the bad gene. It’s possible, though, that your family’s risk was due to some other mutation — in PALB2, or in another undiscovered gene — and in that case the negative test didn’t actually tell you anything. By testing a family member  first, you can be sure you are looking in the right place for your risks, rather than just in the place that’s easiest to test.

August 4, 2014

Predicting blood alcohol concentration is tricky

Rasmus Bååth, who is doing a PhD in Cognitive Science, in Sweden, has written a web app that predicts blood alcohol concentrations using reasonably sophisticated equations from the forensic science literature.

The web page gives a picture of the whole BAC curve over time, but requires a lot of detailed inputs. Some of these are things you could know accurately: your height and weight, exactly when you had each drink and what it was. Some of them you have a reasonable idea about: is your stomach empty or full, and therefore is alcohol absorption fast or slow. You also need to specify an alcohol elimination rate, which he says averages 0.018%/hour but could be half or twice that, and you have no real clue.

If you play around with the interactive controls, you can see why the advice given along with the new legal limits is so approximate (as Campbell Live is demonstrating tonight).  Rasmus has all sorts of disclaimers about how you shouldn’t rely on the app, so he’d probably be happier if you don’t do any more than that with it.

July 29, 2014

A treatment for unsubstantiated claims

A couple of months ago, I wrote about a One News story on ‘drinkable sunscreen’.

In New Zealand, it’s very easy to make complaints about ads that violate advertising standards, for example by making unsubstantiated therapeutic claims. Mark Hanna submitted a complaint about the NZ website of the company  selling the stuff.

The decision has been released: the complaint was upheld. Mark gives more description on his blog.

In many countries there is no feasible way for individuals to have this sort of impact. In the USA, for example, it’s almost impossible to do anything about misleading or unsubstantiated health claims, to the extent that summoning a celebrity to be humiliated publicly by a Senate panel may be the best option.

It can at least produce great television: John Oliver’s summary of the Dr Oz event is viciously hilarious

July 27, 2014

Air flight crash risk

David Spiegelhalter, Professor of the Public Understanding of Risk at Cambridge University, has looked at the chance of getting three fatal plane crashes in the same 8-day period, based on the average rate of fatal crashes over the past ten years.  He finds that if you look at all 8-day periods in ten years, three crashes is actually the most likely way for the worst week to turn out.

He does this with maths. It’s easier to do it by computer simulation: arrange the 91 crashes randomly among the 3650 days and count up the worst week. When I do this 10,000 times (which takes seconds). I get

crashes

 

The recent crashes were separate tragedies with independent causes — two different types of accident and one deliberate shooting — they aren’t related like, say, the fires in the first Boeing Dreamliners were. There’s no reason for the recent events should make you more worried about flying.

July 23, 2014

Average and variation

Two graphs from the NZ influenza surveillance weekly update (PDF, via Mark Hanna)

flu-averageflu-varying

Both show that the seasonal epidemic has started.  I think the second graph is more helpful in comparing this year to the past; showing the actual history for a range of years, rather than an average.  This sort of graph could handle a larger number of past years if they were all or mostly in, eg, thin grey lines, perhaps with this year, last year, and the worst recent year in colour.

The other news in the surveillance update is that the flu viruses that have been examined have overwhelming been H1N1 or H3N2, and both these groups are covered in this year’s vaccine.

The self-surveillance world

See anyone you know? (click to embiggen)

cats

 

This is a screenshot from I know where your cat lives, a project at Florida State University that is intended to illustrate the amount of detailed information available from location-tagged online photographs, without being too creepy — just creepy enough.

(via Robert Kosara and Keith Ng)

July 1, 2014

Facebook recap

The discussion over the Facebook experiment seems to involve a lot of people being honestly surprised that other people feel differently.

One interesting correlation based on my Twitter feed is that scientists involved in human subjects research were disturbed by the research and those not involved in human subjects research were not. This suggests our indoctrination in research ethics has some impact, but doesn’t answer the question of who is right.

Some links that cover most of the issues

June 29, 2014

Not yet news

When you read “The university did not reveal how the study was carried out” in a news story about a research article, you’d expect the story to be covering some sort of scandal. Not this time.

The Herald story  is about broccoli and asthma

They say eating up to two cups of lightly steamed broccoli a day can help clear the airways, prevent deterioration in the condition and even reduce or reverse lung damage.

Other vegetables with the same effect include kale, cabbage, brussels sprouts, cauliflower and bok choy.

Using broccoli to treat asthma may also help for people who don’t respond to traditional treatment.

‘How the study was carried out’ isn’t just a matter of detail: if they just gave people broccoli, they wouldn’t know what other vegetables had the same effect, so maybe it wasn’t broccoli but some sort of extract? Was it even experimental or just observational? And did they actually test people who don’t respond to traditional treatment? And what exactly does that mean — failing to respond is pretty rare, though failing to get good control of asthma attacks isn’t.

The Daily Mail story was actually more informative (and that’s not a sentence I like to find myself writing). They reported a claim that wasn’t in the press release

The finding due to sulforaphane naturally occurring in broccoli and other cruciferous vegetables, which may help protect against respiratory inflammation that can cause asthma.

Even then, it isn’t clear whether the research really found that sulforaphane was responsible, or whether that’s just their theory about why broccoli is effective. 

My guess is that the point of the press release is the last sentence

Ms Mazarakis will be presenting the research findings at the 2014 Undergraduate Research Conference about Food Safety in Shanghai, China.

That’s a reasonable basis for a press release, and potentially for a story if you’re in Melbourne. The rest isn’t. It’s not science until they tell you what they did.