Stuff has an example of the recurring problem of an perfectly good medical science story spoiled by not one, but two appalling headlines.

Currently, on the ‘Wellbeing’ section of the website you see

Feeling poorly? Try Vegemite

and on clicking through to the story

Vegemite may ward off superbugs

The story then goes on to say that high concentrations of niacin, a vitamin found in many foods, including, yes, Vegemite, has been found in test-tube and mouse studies to help in killing bacteria.  It then says

The Internets are full of a story about herbal tea curing breast cancer. The Herald is actually more restrained than many:

An extract commonly found in herbal tea can stop the spread of breast cancer, researchers have found.

That isn’t what the researchers found.  For a start, unless you’re in or near Pakistan, the extract isn’t commonly found in herbal tea.  But that’s not the main problem.

This blog has a tendency to look pro-drug and pro-alcohol, because we react to media stories and these topics are currently popular for exaggeration and over-interpretation.  It’s a nice change to find some serious anti-drug research that the media are reporting pretty sensibly. (Otago Daily Times, Stuff, Herald, 3News, TVNZ)

Researchers in Dunedin, and their international collaborators, used data from the Dunedin Study, which recruited about 1000 babies born in a Dunedin hospital in the 12 months starting April 1972.  These babies, now adults, have given a lot of data up to medical science. In particular, they had a range of neuropsychological tests at age 13 and then again at age 38, and they were interviewed about cannabis use.   The headline results were about IQ, but the study looked at a relatively broad range of cognitive function tests, and also at self-reported problems with memory and attention.   Participants who smoked cannabis as teens had broadly worse cognitive function, by a margin that’s large enough to be a concern.  This didn’t show up in people who started smoking cannabis as adults.  The paper is in PNAS; the abstract is free.

What’s most distinctive about this study is the before-after comparisons.  You often see (and we have pointed out) studies that claim to have found “changes” when they only had one time point, and so really only looked at “differences”.  The Dunedin Study has changes from before cannabis use to after cannabis use.   Also, since the participants are the same age and all from Dunedin, they are less heterogeneous in many ways than participants in other research studies.

The differences in IQ are within the range of the Flynn effect, so it’s still possible that this is a social effect rather than a biochemical one, or that it’s caused by pre-existing differences in people’s interest in the sort of activities that increase IQ test scores, or something.  Better data, however, will be extremely difficult to collect, and treating these results as probably true seems sensible.  Presumably the adverse effects would also be found with synthetic cannabimimetics, but these are too recent for there to be data, and they have other problems not present with cannabis, such as the risk of acute overdose.

A number of the stories quote Ross Bell, of the Drug Foundation, being sensible:

Simply banning drugs such as cannabis and then thinking that was the problem solved would not work, Mr Bell said. “What we’re lacking in New Zealand is support for widespread, high-quality, well-constructed prevention messages targeted at younger people.”

Congratulations to Alan Keegan for nominating* us (!) for a bad graph. Thomas has posted about it here. Congrats Alan!

(* nomination was for the correct time period, but added to the previous week’s nominations page.)

Three sentences from a Herald story 

The Ministry of Transport study used blood samples taken from 453 drivers who caused crashes.

Of that group, 156 were found to be on drugs not administered by a medical professional

Drivers with more than the legal limit of alcohol in their system made up just over half of the 453 samples analysed.

Now try to fill in the blank  in the headline “Tests reveal most crash drivers                                “

If you said “were drunk”, your arithmetic is better than your sense of headlineworthiness, not a problem the Herald had.

A nice page by Christopher Healey, at North Carolina State University.  Among other things, it includes demonstrations of change blindness  and of preattentive perception:

For many years vision researchers have been investigating how the human visual system analyses images. An important initial result was the discovery of a limited set of visual properties that are detected very rapidly and accurately by the low-level visual system. These properties were initially called preattentive, since their detection seemed to precede focused attention. We now know that attention plays a critical role in what we see, even at this early stage of vision. The term preattentive continues to be used, however, since it conveys an intuitive notion of the speed and ease with which these properties are identified.

Typically, tasks that can be performed on large multi-element displays in less than 200 to 250 milliseconds (msec) are considered preattentive. Eye movements take at least 200 msec to initiate, and random locations of the elements in the display ensure that attention cannot be prefocused on any particular location, yet viewers report that these tasks can be completed with very little effort. This suggests that certain information in the display is processed in parallel by the low-level visual system.

The limits of preattentive perception are why you can’t usefully represent more than four or five groups of points in a scatterplot, no matter how creative you get with colours and symbols.

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 August 31 2012.
• Statistics can be bad, exemplary or fascinating.
• The statistic must be in the NZ media during the period of August 25 – 31 2012 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…)

Stuff has a story pointing out that conspiracy theories go together:

If you think smoking doesn’t cause lung cancer, HIV doesn’t cause Aids or Nasa faked the Moon landing, you are also more likely to support free market economics and be sceptical about climate change.

An apparently stronger version of this was demonstrated in a study published in January this year,

A New York Times story about buying and selling favorable online reviews

Many of the 300 reviews he bought through GettingBookReviews were highly favorable, although it’s impossible to say whether this was because the reviewers genuinely liked the books, or because of their well-developed tendency toward approval, or some combination of the two.

[Update: XKCD]

XKCD (come on, you know XKCD): I can’t help but admire the audacity of the marketer who came up with the phrase “contains a clinically studied ingredient”

headsup (journalism blog): It’s more likely that the [Detroit Free Press] doesn’t understand that you’re supposed to do a little basic arithmetic before you talk about public opinion.

Andrew Gelman: graphs showing uncertainty in a fitted curve.

journalism.org.nz: a proposal for NZ public interest journalism funded by the public

BBC: Gathering evidence for the effects of exercise on depression is harder than you might expect.