Inference from studies that make use of data at the level of the area, rather than at the level of the individual, is more dif®cult for a variety of reasons. Some of these dif®culties arise because frequently exposures (including confounders) vary within areas. In the most basic form of ecological study the outcome measure is regressed against a simple area level summary of exposure. In the aggregate data approach a survey of exposures and confounders is taken within each area. An alternative approach is to assume a parametric form for the within-area exposure distribution. We provide a framework within which ecological and aggregate data studies may be viewed, and we review some approaches to inference in such studies, clarifying the assumptions on which they are based. General strategies for analysis are provided including an estimator based on Monte Carlo integration that allows inference in the case of a general risk±exposure model. We also consider the implications of the introduction of random effects, and the existence of confounding and errors in variables.

Background/objectives To examine the association of body mass index (BMI) with change in children's physical activity and sedentary time between ages 6 and 11. Participants A total of 2132 children participated from 57 schools in Southwest England, from the B-PROACT1V study. Methods Mean minutes of MVPA and sedentary time per day were derived from accelerometer-based measurements at ages 6, 9 and 11. Linear multilevel models examined the association of BMI categories with MVPA and sedentary time between 6 and 11, adjusting for seasonality, wear time, gender and household education. Differences in change over time were examined using interaction terms. Results Average weekday MVPA decreased between ages 6 and 11 by 2.2 min/day/year (95% CI: 1.9 to 2.5), with a steeper decline at weekends. Average sedentary time increased at a rate of 12.9 min/day/year (95% CI: 12.2 to 13.6). There were no differences in mean levels of MVPA by BMI categories at age 6, but differences emerged as children aged, with the gap between children who were healthy weight and overweight increasing by 1.7 min/day (95% CI: 0.8-2.6) every year, and between healthy and obese by 2.0 min/day (95% CI: 0.9-3.1) each year. Children who were overweight/obese engaged in less average weekday sedentary time at age 6 than those of healthy weight, but the gap closed by age 11. Conclusion MVPA declines and sedentary time increases on average for all children between ages 6 and 11. While there are no differences in activity levels by BMI category at age 6, differences in MVPA emerge over time for those who are overweight and obese. Developing interventions that support children to retain activity levels as they approach older childhood, particularly those who are overweight/obese could improve public health.

Background Restrictions due to the coronavirus disease 2019 (COVID-19) pandemic reduced physical activity provision for both children and their parents. Recent studies have reported decreases in physical activity levels during lockdown restrictions, but these were largely reliant on self-report methods, with data collected via unrepresentative self-report surveys. The post-pandemic impacts on children’s activity levels remain unknown. A key question is how active children become once lockdown restrictions are lifted. Methods Active-6 is a repeated cross-sectional natural experiment. Accelerometer data from 1296 children aged 10–11 and their parents were collected in 50 schools in the Greater Bristol area, UK in March 2017-May 2018 (pre-COVID-19 comparator group), and compared to 393 children aged 10–11 and parents in 23 of the same schools, collected in May-December 2021. Mean minutes of accelerometer-measured moderate-to-vigorous physical activity (MVPA) were derived for weekdays and weekend and compared pre- and post-lockdown via linear multilevel models. Results After adjusting for seasonality, accelerometer wear time and child/parent demographics, children’s mean weekday and weekend MVPA were 7.7 min (95% CI: 3.5 to 11.9) and 6.9 min (95% CI: 0.9 to 12.9) lower in 2021 than in 2018, respectively, while sedentary time was higher by 25.4 min (95% CI: 15.8 to 35.0) and 14.0 min (95% CI: 1.5 to 26.5). There was no evidence that differences varied by child gender or household education. There was no significant difference in parents’ MVPA or sedentary time, either on weekdays or weekends. Conclusions Children’s MVPA was lower by 7–8 min/day in 2021 once restrictions were lifted than before the pandemic for all groups, on both weekdays and weekends. Previous research has shown that there is an undesirable age-related decline in children’s physical activity. The 8-min difference reported here would be broadly comparable to the decline that would have previously been expected to occur over a three-year period. Parents’ physical activity was similar to pre-pandemic levels. Our results suggest that despite easing of restrictions, children’s activity levels have not returned to pre-pandemic levels. There is an urgent need to understand why these changes have occurred and how long they are maintained.

AimsTo introduce an 'opt out' referral pathway for smoking cessation in pregnancy and to compare different methods for identifying pregnant smokers in maternity care. Design Pilot study that analysed routine data from maternity and smoking cessation services with biochemical validation of smoking status. Setting Dudley and South Birmingham, England. Participants A total of 3712 women who entered the referral pathway-1498 in Dudley and 2214 in South Birmingham. Measurements Routine monitoring data on smoking at maternity booking, referral to smoking cessation services, number of women who set quit dates set and short-term (4-week) self-report smoking status. Comparison of self-report, carbon monoxide (CO)-validated and urinary cotinine-validated smoking status for a subsample (n = 1492) of women at maternity booking. Findings In Dudley 27% of women who entered the opt out referral pathway were identified as smokers following CO testing. Of those referred to the smoking cessation services, 19% reported stopping smoking at 4-week follow-up. In South Birmingham 17% were smokers at booking, with 5% of those referred recorded as non-smokers at 4 weeks. The number of women quitting did not increase during the study when compared with the previous year, despite higher referral rates in both areas. An optimum cut-off CO measurement of 4 parts per million (p.p.m.) was identified for sensitivity and specificity. Conclusion The introduction of an opt out referral pathway between maternity and stop smoking services resulted in more women being referred for support to quit but not higher numbers of quitters, suggesting that automatic referral may include women who are not motivated to stop and who may not engage with services. Routine carbon monoxide monitoring introduced as part of a referral pathway should involve a cut-off of 4 p.p.m. to identify smoking in pregnancy.

AimsTo measure the impact of the suspension of tobacco control mass media campaigns in England in April 2010 on measures of smoking cessation behaviour. Design Interrupted time series design using routinely collected population-level data. Analysis of use of a range of types of smoking cessation support using segmented negative binomial regression. Setting England. Measurements Use of non-intensive support: monthly calls to the National Health Service ( , and quitline calls and web hits fell by 65% (95% CI = 43-79) and 34% (95% CI: 11-50), respectively. The number of people setting a quit date and 4-week quitters at the SSS increased throughout the study period. Conclusions The suspension of tobacco control mass media campaigns in England in 2012 appeared to markedly reduce the use of smoking cessation literature, quitline calls and hits on the national smoking cessation website, but did not affect attendance at the Stop Smoking Services. Within a comprehensive tobacco control programme, mass media campaigns can play an important role in maximizing quitting activity.