Posts filed under Medical news (215)

April 14, 2014

What do we learn from the Global Drug Use Survey?

drug

 

That’s the online summary at Stuff.  When you point at one of the bubbles it jumps out at you and tells you what drug it is. The bubbles make it relatively hard to compare non-adjacent numbers, especially as you can only see the name of one at a time. It’s not even that easy to compare adjacent bubbles, eg, the two at the lower right, which differ by more than two percentage points.

More importantly, this is the least useful data from the survey.  Because it’s a voluntary, self-selected online sample, we’d expect the crude proportions to be biased, probably with more drug use in the sample than the population. To the extent that we can tell, this seems to have happened: the proportion of past-year smokers is 33.5% compared to the Census estimate of 15% active smokers.  It’s logically possible for both of these to be correct, but I don’t really believe it.  The reports of cannabis use are much higher than the (admittedly out of date) NZ Alcohol and Drug Use Survey.  For this sort of data, the forthcoming drug-use section of the NZ Health Survey is likely to be more representative.

Where the Global Drug Use Survey will be valuable is in detail about things like side-effects, attempts to quit, strategies people use for harm reduction. That sort of information isn’t captured by the NZ Health Survey, and presumably it is still being processed and analysed.  Some of the relative information might be useful, too: for example, synthetic cannabis is much less popular than the real thing, with past-year use nearly five times lower.

April 8, 2014

Asthma inhalers and diet: shorter, with more swearing

Ok, so the previous post is about Herald (Daily Mail) story on asthma research. As science reporting goes it’s no worse than usual for these Mail reprints. The reason for this second post is that I read the story again and thought about health reporting.

The story lead says

Eating fast food and consuming sugary drinks renders the most common asthma inhaler ineffective, a study warns.

 That is, the Herald is telling people their emergency asthma inhaler will not work if they eat certain foods. There’s no suggestion of what to do instead in an attack or who to call for help. Even if the claim were true, that would be irresponsible. When it’s just linkbait, it’s fscking appalling.

Overinterpreting diet and asthma

The Herald’s lead

Eating fast food and consuming sugary drinks renders the most common asthma inhaler ineffective, a study warns.

This is two studies. One looked at a ‘dietary inflammation index’ and whether people with higher values were more likely to be asthmatic. It did not look at inhaler effectiveness at all.  The dietary inflammation index does not measure ‘sugary drinks’; it treats all carbohydrate the same. It doesn’t directly measure fast food, though it does distinguish different types of fat.  Since the dietary inflammation index, according to the paper that proposed it, is relatively weakly associated with biological measures of inflammation,  the strong association seen in this study between the index and asthma may just mean that other factors are affecting both asthma and diet.

The other study looked at how salbutamol, the active ingredient of the Ventolin inhaler, was absorbed in samples of lung tissue in the lab. The amount of polyunsaturated fat affected absorption — but that wasn’t dietary fat and there weren’t any inhalers, or any sugary drinks.  Further research might show this translates into real differences in inhaler effectiveness, or it might not.

So, while there is actual science described in the article, there is almost no support for the lead. No inhalers, no sugary drinks, no fast food.

You might also wonder why the Herald is getting a comment from Asthma UK for research presented at a conference of the Thoracic Society of Australia and New Zealand. Or not.

March 29, 2014

WiFi context

Age-adjusted brain cancer diagnoses and deaths in the US over time (SEER)

brain

 

The IEEE 802.11a standard was published in 1999 and was first called WiFi in 2000.  WiFi exposure has increased dramatically since then. You can see what the trend in brain cancer has been.

The International Agency for Cancer Research (IARC) lists WiFi as a ‘possible’ human carcinogen. That doesn’t mean they think it’s actually causing cancer. That means there’s enough uncertainty that they can’t rule out the possibility that it would cause cancer at some dose.

A cancer ‘hazard’ is an agent that is capable of causing cancer under some circumstances, while a cancer ‘risk’ is an estimate of the carcinogenic effects expected from exposure to a cancer hazard. The Monographs are an exercise in evaluating cancer hazards, despite the historical presence of the word ‘risks’ in the title. The distinction between hazard and risk is important, and the Monographs identify cancer hazards even when risks are very low at current exposure levels, because new uses or unforeseen exposures could engender risks that are significantly higher.

It’s quite hard to rule this sort of thing out, which is why out of the 970 agents IARC has classified, only one has been labelled “probably not carcinogenic to humans”. That one wasn’t radiofrequency electromagnetic fields, but if you read the summary of the monograph (PDF) you find it’s cellphones held to the ear that are the possible risk they were concerned about.

This information may be helpful context if you read the Dominion Post.

 

 

March 21, 2014

Common exposures are common

A California head-lice treatment business has had huge success in publicising its business with the claim that selfies are causing a  rise in nits among teenagers. The Herald mentions this in Sideswipe, the right place for this sort of story, but other international sites have been less discriminating.

There are no actual numbers involved, and nothing like representative data even if you’re in the South Bay area of central California. More importantly, though, there is no comparison group. The owner of the business, Mary MacQuillan, says “Every teen I’ve treated, I ask about selfies, and they admit that they are taking them every day.”  That’s probably only a slight exaggeration at most, but every teen she hasn’t treated has also probably been taking photos that way. It’s something teenagers do.  Common exposures are common.

So, why were news organisations around the world publicising this? The fact that it’s about teenagers and the internet goes a long way to explaining it.  It doesn’t need evidence because teenage use of technology is automatically scary and newsworthy: as Ms MacQuillan says ” I think parents need to be aware, and teenagers need to be aware too. Selfies are fun, but the consequences are real.”

You get the same thing happening with ‘chemicals’, as the dihydrogen monoxide parody website loves to point out

A recent stunning revelation is that in every single instance of violence in our country’s schools, …, dihydrogen monoxide was involved.

 

March 18, 2014

Your gut instinct needs a balanced diet

I linked earlier to Jeff Leek’s post on fivethirtyeight.com, because I thought it talked sensibly about assessing health news stories, and how to find and read the actual research sources.

While on the bus, I had a Twitter conversation with Hilda Bastian, who had read the piece (not through StatsChat) and was Not Happy. On rereading, I think her points were good ones, so I’m going to try to explain what I like and don’t like about the piece. In the end, I think she and I had opposite initial reactions to the piece from on the same starting point, the importance of separating what you believe in advance from what the data tell you. (more…)

March 16, 2014

Same number of workers being caught on drugs?

The Herald said, on Friday “Fewer workers stoned on the job

Information from the New Zealand Drug Detection Agency showed 81,410 on-site drug-screening tests were carried out last year, 16 per cent up from the previous year.

But only 5.5 per cent of tests showed the presence of drugs, down from 6.4 per cent in 2013

As usual, there’s no mention of the fact that NZDDA is just one of the private companies offering drug testing services. It took me a long time to realise this, until I was tipped off by a news story advertising one of their competitors.

Presumably NZDDA don’t think their customers choose them at random, and with no real reason for wanting testing. If customers were behaving even a little rationally you’d expect an expansion of drug testing to pull in lower-risk employees. If we look at the actual number of positive tests, using the quoted figures, it was about 4480 last year and about 4490 in the previous year. Given no change in the number of positive tests and a 1 percentage point change in the proportion of positive tests, from a single company, there’s not a lot of numerical evidence for an increase in number of workers with detectable cannabis in their systems.

More importantly, there’s no evidence whatsoever for the ‘stoned on the job’ headline: absolutely no information is given about this. One of the big problems with cannabis testing is that there is no useful biochemical assay for being stoned. Detectable levels persist long after impairment is over, and even when you’re actually stoned there is not a good relationship between drug concentration and impairment.  This is a real problem for Washington and Colorado, which have legalised cannabis and need to set driving laws. In contrast to alcohol, if you actually care about safe driving and cannabis, it’s really hard to get a useful and objective test.

The story ends with two examples of disasters. In one, cannabis was definitely ruled out as a contributing factor; in the other, the conclusion was only that “it could not be excluded”. The NZDDA  press release is at Scoop, and despite how the story reads, there is surprisingly little text in common.

March 6, 2014

Attack of the killer lamb?

Not, not that one, the story about eating meat.

Stuff has the more egregious version “Eating meat ‘as bad as smoking‘”, the Herald has the rather better “Protein packed diet nearly as bad as smoking – expert”.

First, the good bits. Both stories are better than the UK versions: the Herald talks to Australian experts and brings in a related study; the Fairfax story at least mentions an outside scientific opinion and gives a link (though it’s to the university press release, which doesn’t link further to the research paper).

The researchers compared people who ate high-protein diet (just under 20% of the people) to those who ate a low-protein diet (just over 5%), and found a 70% higher rate of death in the high-protein group, in people aged 55-64.  The study was observational, but it was in a representative sample of the US and was backed up by experiments in mice. That’s not completely reliable,  but it is a big step.

The 70%-higher-rate of death for  high-protein vs low-protein diets compares to slightly over 100% higher rate for current smokers vs non-smokers in previous research using data from the same survey. You could get away with calling that ‘nearly as bad’, especially as other surveys have tended to give smaller differences. So, the Herald’s headline is defensible. Stuff’s headline drops the ‘nearly’, the ‘packed’ and refers to ‘meat’ rather than ‘protein’. It would be easy for a casual reader to get the false impression that the research had found eating meat was as bad as smoking.

There are two really big holes in the coverage, though.  The Herald alludes to one of them but doesn’t follow up 

People on high-protein diets are likely to lose years of life along with the weight they shed, according to two studies.

All the statistical analyses in the paper attempted to control for weight, ie, they were trying to compare people on high and low protein diets with the same weight. That’s not the relevant question for many people on these diets — the attraction of the diet is that it’s easier to lose weight.  The relevant question for them is a comparison between a high-protein diet with lower weight or a low-protein diet with higher weight.  That question could have been addressed with the data, but it wasn’t.

A rather less subtle omission is that neither story, nor the press release, mentions a key point of the paper: that the association reverses in people over 65.

March 4, 2014

What you do know that ain’t so

From a randomised trial of four different sets of information about vaccine benefits (via Brendan Nyhan)

Parents were randomly assigned to receive 1 of 4 interventions: (1) information explaining the lack of evidence that MMR causes autism from the Centers for Disease Control and Prevention; (2) textual information about the dangers of the diseases prevented by MMR from the Vaccine Information Statement; (3) images of children who have diseases prevented by the MMR vaccine; (4) a dramatic narrative about an infant who almost died of measles from a Centers for Disease Control and Prevention fact sheet; or to a control group.

In particular, intervention 4 is a popular and sensible idea, and it has occurred to people from Benjamin Franklin to Kiwi parents and the Herald. However:

RESULTS: None of the interventions increased parental intent to vaccinate a future child. Refuting claims of an MMR/autism link successfully reduced misperceptions that vaccines cause autism but nonetheless decreased intent to vaccinate among parents who had the least favorable vaccine attitudes. In addition, images of sick children increased expressed belief in a vaccine/autism link and a dramatic narrative about an infant in danger increased self-reported belief in serious vaccine side effects.

This research is depressing from the point of view of science communication. The problem is that the message goes in two apparently opposite ways.  One conclusion is that increasing trust in science and medicine is the only solution, which would require more public contact and communication, and openness about uncertainty.  The other conclusion is that a public health advertising campaign is a treatment, and like any other treatment it should be evaluated for safety and effectiveness before it’s applied to the population, an approach that seems to imply a reduction in open and unfiltered communication.

I don’t think the contradiction is unavoidable; I think more communication about research process — who are we and what do we actually do — will help, but also that advertising, whether government-funded or pushed by PR departments, is actually dangerous.  If we overstate claims about the biochemical effects of compounds in chocolate, or the number of deaths prevented by lowering the blood alcohol limit, why should we be trusted on important issues?

 

February 27, 2014

They couldn’t hit an elephant at this dist…

James Russell sent me a link to this story from a Canadian paper (originally from the Daily Telegraph).  The Herald has it too, with a very slightly less naff picture.  The research (open access) is good; the story is reasonably informative, but seriously credulous

Blood samples from over 17,000 generally healthy people were screened for 100 biomarkers, and those people monitored over five years.

In that time, 684 died from illnesses including cancer and cardiovascular disease. They all had similar levels of four biomarkers: albumin; alpha-1-acid glycoprotein; citrate, and a similar size of very-low-density lipoprotein particles.

Compare the last sentence to this graph from the research paper. The vertical axis is a combined score on the four biomarkers. The red dots are the people who died. As you can see, they didn’t all have similar values.

journal.pmed.1001606.g004

 

The research is impressive not because the prediction is very accurate, but because its less appalling inaccurate than usual.  Using standard risk factors (age, sex, cholesterol, smoking, diabetes, cancer) if you picked a random person who died and one who didn’t die from their cohort there’s an 80% chance the one with the worse risk factors was the one who died.  Adding the ‘death test’ measurements increases the probability to 83%.  Asking an experienced nurse to guess would probably be more accurate (and cheaper), but is hard to automate.

Despite the impression from the headline and lead, if you’re asked to predict whether someone will live another year, based on this sort of information, the safe bet is “yes”. Even among the 1% of people with the very worst values of the ‘death test’ biomarkers, 80% lived for more than a year and half were still alive at the end of the five year study.

Interestingly, the two republished versions lack the last paragraphs of the original Telegraph story, which talk about whether the test is useful

“If the findings are replicated then this test is surely something we will see becoming widespread,” added Prof Perola.

“But at moment there is ethical question. Would someone want to know their risk of dying if there is nothing we can do about it?”

Dr Kettunen added: “Next we aim to study whether some kind of connecting factor between these biomarkers can be identified.