MPH Master pieces

More teenage sex

Here is a paper that got a lot of press coverage. At first glance it appears to show that an intervention designed, among other things, to reduce teenage pregnancy had the opposite effect. With hindsight it seems obvious: bring together a bunch of rebellious teenagers and they'll end up having sex; what's more it'll be unprotected sex.

An accompanying editorial provides some context. Britain had the highest teenage pregnancy in Europe; a programme in America seemed to reduce teenage pregnancy by half; who wouldn't want to try it over here? Two problems with this.

Firstly what is the 'it' we want to try? What exactly do we replicate? Trial programmes are run by enthusiasts; results always degrade with wide spread (in our case nation-wide) implementation. You can't replicate enthusiasm.

Secondly the headline result from the USA provided only a partial picture from six of 12 pilot sites. Results from all 12 sites showed no benefit.

Even so, reversal of effect is unexpected, and we must congratulate the Department of Health policy research team for commissioning this evaluation.

Meanwhile over at the Times newspaper, an editorial ponders the difficulty of basing policy on evidence. It's not as easy as you think.

Death in Siberia and alcohol

Life expectancy in Russia has swung wildly up and down over the past 20 years. Here is a massive study, based in three Siberian cities, which shows how much of this is due to alcohol. The short answer - a lot.

The study used a simple case-comparison method, but on a massive scale. Given the effort involved there must be many more papers to come.

Dementia - concurrent validation of a test

 This paper reports a new 'screening' test for Alzheimers disease. More below on use of the word 'screening' in this context.

Good points:

a. validated against people with a firm clinical diagnosis, made by experts, of Alzheimers disease (i.e. concurrent validation, against a 'gold standard');

b. ROC comparison against the current screening test - the Mini Mental State Exam. The correct way to compare two screening tests is the ROC curve.

c. age specific norms published - i.e. what 'normal' people score on this test.

Although the test is described as a screening test I would classify it as a clinical algorithm, given its intended use in hosptial and other clinics. I certainly hope it won't be used in the general population without more validation, though unfortunately the authors have put the test on a website for anyone to try. 

There is some debate about whether tests like this are 'screening' or not.  Both population screening and clinical testing start with a prior probability of disease which changes to a higher (or lower)probability after the result is known. In a clinical setting the prior probability of disease is higher: the patient has come to the clinic because something is wrong.

On the other hand the ethics are certainly different. In population screening we invite ordinary people who are happily going about their business and tell them they may have some serious disease. With clinical tests, the doctor is sifting through the possibilities for someone who has asked what is wrong with them.

Salt!

Here is an excellent summary of the scientific position on salt. Skip the tables and read the text. Like flu, this is a 'must know' for anyone in public health.