Here is an evaluation of the effect of the smoke-free laws in Scotland. This is one of those things we absolutely need to know about if we are in public health but the paper, particularly the methods section, is not an easy read. The basic design is a questionnaire survey.
There are two difficult bits in the methods section. Firstly the survey respondents were recruited in several different survey waves with top-up samples for drop out. All this will give plenty of material for the tobacco companies to rubbish the research. Our task is to form a balanced judgement about whether the resulting sample is likely to give us truth or not - and to accept that we may have to conclude with regret that it does not. Important to be alert to flaws, particularly when research appears to say what we want it to say.
The other difficult bit in the methods section is the statistical methodology. There is a lot of weighting to make the samples representative of the base populations. But more tricky for the non-statistician is the use of generalised estimating equations (GEE). The main benefit of using GEE is to get right (or as right as possible) the confidence intervals on all the results. But it also permits analysis of interactions between variables. As the authors point out, the key question is whether the various measures changed more in Scotland than in the rest of the UK. They have before-and-after measures (i.e two waves of results) in two areas, so technically speaking they are looking for a wave-by-area interaction.