Natural experimental studies are often recommended as a way of understanding the health impact of policies and other large scale interventions. Although they have certain advantages over planned experiments, and may be the only option when it is impossible to manipulate exposure to the intervention, natural experimental studies are more susceptible to bias. This paper introduces new guidance from the Medical Research Council to help researchers and users, funders and publishers of research evidence make the best use of natural experimental approaches to evaluating population health interventions. The guidance emphasises that natural experiments can provide convincing evidence of impact even when effects are small or take time to appear. However, a good understanding is needed of the process determining exposure to the intervention, and careful choice and combination of methods, testing of assumptions and transparent reporting is vital. More could be learnt from natural experiments in future as experience of promising but lesser used methods accumulates

Background Previous studies have suggested a reduction in the total number of hospital admissions for acute coronary syndrome after the enactment of legislation banning smoking in public places. However, it is unknown whether the reduction in admissions involved nonsmokers, smokers, or both. Methods

The close correspondence between energy intake and expenditure over prolonged time periods, coupled with an apparent protection of the level of body adiposity in the face of perturbations of energy balance, has led to the idea that body fatness is regulated via mechanisms that control intake and energy expenditure. Two models have dominated the discussion of how this regulation might take place. The set point model is rooted in physiology, genetics and molecular biology, and suggests that there is an active feedback mechanism linking adipose tissue (stored energy) to intake and expenditure via a set point, presumably encoded in the brain. This model is consistent with many of the biological aspects of energy balance, but struggles to explain the many significant environmental and social influences on obesity, food intake and physical activity. More importantly, the set point model does not effectively explain the ‘obesity epidemic’ – the large increase in body weight and adiposity of a large proportion of individuals in many countries since the 1980s. An alternative model, called the settling point model, is based on the idea that there is passive feedback between the size of the body stores and aspects of expenditure. This model accommodates many of the social and environmental characteristics of energy balance, but struggles to explain some of the biological and genetic aspects. The shortcomings of these two models reflect their failure to address the gene-by-environment interactions that dominate the regulation of body weight. We discuss two additional models – the general intake model and the dual intervention point model – that address this issue and might offer better ways to understand how body fatness is controlled.

OBJECTIVE To detect any change in exposure to secondhand smoke among primary schoolchildren after implementation of smoke-free legislation in Scotland in March 2006. DESIGN Comparison of nationally representative, cross sectional, class based surveys carried out in the same schools before and after legislation. SETTING Scotland. PARTICIPANTS 2559 primary schoolchildren (primary 7; mean age 11.4 years) surveyed in January 2006 (before smoke-free legislation) and 2424 in January 2007 (after legislation). OUTCOME MEASURES Salivary cotinine concentrations, reports of parental smoking, and exposure to tobacco smoke in public and private places before and after legislation. RESULTS The geometric mean salivary cotinine concentration in non-smoking children fell from 0.36 (95% confidence interval 0.32 to 0.40) ng/ml to 0.22 (0.19 to 0.25) ng/ml after the introduction of smoke-free legislation in Scotland-a 39% reduction. The extent of the fall in cotinine concentration varied according to the number of parent figures in the home who smoked but was statistically significant only among pupils living in households in which neither parent figure smoked (51% fall, from 0.14 (0.13 to 0.16) ng/ml to 0.07 (0.06 to 0.08) ng/ml) and among pupils living in households in which only the father figure smoked (44% fall, from 0.57 (0.47 to 0.70) ng/ml to 0.32 (0.25 to 0.42) ng/ml). Little change occurred in reported exposure to secondhand smoke in pupils' own homes or in cars, but a small decrease in exposure in other people's homes was reported. Pupils reported lower exposure in cafes and restaurants and in public transport after legislation. CONCLUSIONS The Scottish smoke-free legislation has reduced exposure to secondhand smoke among young people in Scotland, particularly among groups with lower exposure in the home. We found no evidence of increased secondhand smoke exposure in young people associated with displacement of parental smoking into the home. The Scottish smoke-free legislation has thus had a positive short term impact on young people's health, but further efforts are needed to promote both smoke-free homes and smoking cessation

No abstract

National studies need to be conducted to examine how widespread the problem identified is and tobacco control initiatives and smoking cessation treatment services need to consider urgently how to overcome the barrier that a desire on the part of young people to continue cannabis smoking poses to achieving a reduction in tobacco use.

OBJECTIVE To measure change in adult non-smokers' exposure to secondhand smoke in public and private places after smoke-free legislation was implemented in Scotland. DESIGN Repeat cross sectional survey. SETTING Scotland. PARTICIPANTS Scottish adults, aged 18 to 74 years, recruited and interviewed in their homes. INTERVENTION Comprehensive smoke-free legislation that prohibits smoking in virtually all enclosed public places and workplaces, including bars, restaurants, and cafes. OUTCOME MEASURES Salivary cotinine, self reported exposure to smoke in public and private places, and self reported smoking restriction in homes and in cars. RESULTS Overall, geometric mean cotinine concentrations in adult non-smokers fell by 39% (95% confidence interval 29% to 47%), from 0.43 ng/ml at baseline to 0.26 ng/ml after legislation (P<0.001). In non-smokers from non-smoking households, geometric mean cotinine concentrations fell by 49% (40% to 56%), from 0.35 ng/ml to 0.18 ng/ml (P<0.001). The 16% fall in cotinine concentrations in non-smokers from smoking households was not statistically significant. Reduction in exposure to secondhand smoke was associated with a reduction after legislation in reported exposure to secondhand smoke in public places (pubs, other workplaces, and public transport) but not in homes and cars. We found no evidence of displacement of smoking from public places into the home. CONCLUSIONS Implementation of Scotland's smoke-free legislation has been accompanied within one year by a large reduction in exposure to secondhand smoke, which has been greatest in non-smokers living in non-smoking households. Non-smokers living in smoking households continue to have high levels of exposure to secondhand smoke

The observed clustering, and shared underlying determinants, of risk behaviours in young people has led to the proposition that interventions should take a broader approach to risk behaviour prevention. In this review we synthesized the evidence on 'what works' to prevent multiple risk behaviour (focusing on tobacco, alcohol and illicit drug use and sexual risk behaviour) for policy-makers, practitioners and academics. We aimed to identify promising intervention programmes and to give a narrative overview of the wider influences on risk behaviour, in order to help inform future intervention strategies and policies. The most promising programme approaches for reducing multiple risk behaviour simultaneously address multiple domains of risk and protective factors predictive of risk behaviour. These programmes seek to increase resilience and promote positive parental/family influences and/or healthy school environments supportive of positive social and emotional development. However, wider influences on risk behaviour, such as culture, media and social climate also need to be addressed through broader social policy change. Furthermore, the importance of positive experiences during transition periods of the child-youth-adult phase of the life course should be appropriately addressed within intervention programmes and broader policy change, to reduce marginalization, social exclusion and the vulnerability of young people during transition periods.