MPH Master pieces

Smoking laws

Laws which restrict certain actions provoke controversy so it's up to us to know the evidence. (Notice I said 'restrict certain actions' not 'curtail certain freedoms' - words matter. As scientists we should try to remain as objective as possible and 'freedom' is one of the least objective words in the dictionary.)

This is low grade evidence but it's an important question. England and Ireland have passed strong smoke-free laws; in the Netherlands the laws are weaker. So that sets up a natural experiment to compare comprehensive versus partial legislation. The data in this paper are from annual surveys of a cohort which (if I have read the report correctly) maintains response rates over 75%.

The statistical handling is complex, with 'generalised estimating equations' to handle the problem of repeat analysis on the same set of people, and also as the authors point out, of the central question:

Of key interest in this study is the period by country interaction, as it allows for formal testing of whether quit attempts and/or success evolved over the two time periods differently in each of the three countries.

Comprehensive legislation also seems to create more support among smokers than partial bans. 

 

Risk factors are risk factors

If smoking increases the risk of cardiovascular disease among men with white skin in the northern USA, do we need to repeat the study in men with black skin / women / people in Japan etc etc. Or the effect of a toxic substance on the coronary endothelium the same for everyone?

This is a difficult one. Viewed purely as endothelium, then you would have to say that toxins are toxins. But viewed as part of a human being, then you worry about whether oestrogens or characteristic diets or whatever might modify the influence of the toxins on the endothelium.

Here is a study looking at risks for cardiovascular disease. It is a meta-analysis of 18 cohort studies and the authors managed to get hold of the individual data from each study, not merely the averages reported in publications. This is strong methodology.

Bottom line: Male or female, black or white, then or now - if you have low cholesterol, low blood pressure, don't smoke and are not diabetic your changes of a heart attack or stroke are small.

Self harming adolescents

 About 50 years ago, the great Jerry Morris wrote a book called 'Uses of Epidemiology'. One use was to set out clearly the natural history of a condition - what happens as time passes.

So here is a nice study of adolescents from Victoria in Australia. A cohort of teenagers were recruited and followed up through seven waves of interviews until they were about 30 years old. In adolescence, 8% were self harming, but that dropped to 1% in adulthood. Most of those still harming themselves in adulthood were women, with only 1 of the 722 boys still self harming.

We could be picky about one or two aspects of the study, particularly the use of self report on harming behavious. Even so, it's pretty impressive to recruit that many teenagers and retain them through seven waves of followup. Maybe that's the sort of place Melbourne is. (But maybe also that means these findings wouldn't apply in other, more chaotic cityscapes.)

 

 

 

... and now too old at 45?

If this goes on we'll all be too old to do anything as soon as we leave university.

The latest paper from the famous Whitehall II cohort study looked at cognitive function. It's a good write up with the strengths and limitations of the research well set out. The effects of age on cognitive functions are different in men and women (i.e. an age x sex interaction) so the results are presented separately for each sex.

All that said, I'm not sure what the practical implication is. We know that as we get older our sight, hearing, strength and pretty much everything else diminishes, so it's not surprising that the same applies to several brain function. Sometimes research is interesting but you're not quite sure what to do about it, other than tuck the findings away at the back of your mind for future reference.

Assuming you don't forget it in the meantime .