MPH Master pieces

Violent drunk kids

Seems like this should be important. The findings in a nutshell:

"Among adolescents identified in the ED with self-reported alcohol use and aggression, a brief intervention resulted in a decrease in the prevalence of self-reported aggression and alcohol consequences"

so what about the study? Excellent design and analysis (RCT, outcome assessors blinded, theory driven intervention, intervention fidelity assured by taping all the motivational interviews) and impressive recruitment and retention rates. The intervention was described as 'brief' which in this case means 35 minutes. That's probably ok for interventions delivered by trained counsellors, and the report says they were able to work around whatever medical care was going on at the time.

One or two weaknesses - one-sided P values (I've grumbled about this before, perhaps it's an American thing?) and of course the reports on alcohol and aggression are self report.

Note that the control groups also showed hefty changes, albeit not as large as the intervention groups. Worth mulling over why this should have happened - it's not quite a placebo effect.

I'm also pleased that a real person still does better in motivating change than a computer.

All in all, plenty to think about.

Preventing adolescent drug use

The past decade has started to see success in efforts to prevent adolescents from doing what comes naturally to them - being delinquent and taking drugs. Here is a trial of 'Communities that care'. The concept was interesting - not a standardised package but a framework for allowing each community to do its own local survey and then set its own priorities. They are however required to choose their interventions from an evidence based menu. All looks good, but note that these are small communities - about 15 000 population, with some barely 2 000.

Next up (but maybe not for another decade or two)  - how to stop teenagers from having sex.

Counting intravenous drug users

Here's a classic of its type. Counting the number of Iv drug users in an area is, for some obvious reasons, difficult.

Capture-recapture methods come from ecology. If you want to count butterflies in a wood, capture ten and mark them with a spot. Come back a week later and capture another ten. How many of this recapture sample are already marked? Two - i.e. 20%? Then your first effort must have captured 20% of the entire population; there are 50 butterflies in the wood altogether.

The Bristol team use a variant of this. Rather than capture- recapture at different points in time, they look for overlap (patients already 'marked,' as it were) in different data sources. For this to work properly the sources must be independent - getting arrested should make no difference to whether or nor you are attending a treatment agency. Then they add a sophistication I don't fully understand - the 'covariate' method.

All in all they found lower death rates than expected (though still appallingly high); a lot of hepatitis B and a lot of undiganosed hepatitis C. The result of all this?

"As a result Bristol PCT increased investment in needle and syringe provision, HCV diagnostic testing, and renewed its efforts to reduce injecting risk and BBV transmission locally. Without the local information showing the scale of the risk the commitment and a sense of urgency by providers and policymakers may not have emerged as quickly. In contrast, the public health message from the mortality study was that the high coverage of O[piate] S[ubstitution] T[herapy] was improving the health of the population, and led to a local commitment to maintain current levels of provision and increase the uptake of OST."

Confirms the opinion expressed 20 years ago in an obscure (but brilliant!) doctoral thesis that the purpose of local epidemiology is not to generate new knowledge but to prompt action; and hence the requirement is for info that is local and immediate. It doesn't have to be accurate to the last decimal point. (But it does have to be rigorous enough to be honest.)

An impressive school programme

Might be worth checking this research out in person - the study area is Hawaii!

Solid research, strong and lasting results on substance use, violence and sexual behaviour e.g. 'carried a knife to use to hurt someone': 9% in the control group and 2.7% in the intervention group.

Note the details of the intervention - school-wide, family and community components, lasted from kindergarten through 12th grade. The authors also point out that the results really only start to bite after three years (message to research funders - stay with it for 5 years or more!).

Just one fly in the ointment - the authors (a) use one sided significance tests, (b) cite 90% confidence intervals instead of the usual 95% and (c) make no adjustment for multiple comparisons. Their results are impressive so why such dubious statistical practices, all of which will tend to overstate statistical significance?