Gastroesophageal reflux disease (GERD) is estimated to affect up to one-quarter of the Italian population, generating immense treatment costs. An emergent surgical treatment involving implantation of a nonactive device, RefluxStop, is offered at a number of hospitals in Italy and several other European countries. Published clinical outcomes of this device from the Conformité Européenne (CE)-mark clinical trial and real-world settings are consistently encouraging and with a favorable safety profile. This study evaluated the cost-effectiveness of RefluxStop compared with the current medical and surgical standards of care in Italy. A Markov model recently developed for use in the United Kingdom was adapted to the Italian healthcare payer’s perspective, covering the GERD treatment field. The model incorporated a lifetime horizon, one-month cycle length, and a 3

The term 'natural experiment’ has a murky conceptual history in public health, with definitions ranging from naturally occurring states to unspecified approximations of randomised trials. Craig and colleagues recently defined natural experiments as events creating exposed and unexposed groups outside researcher control, but this is largely indistinguishable from any observational study. One could define natural experiments as cases of randomised treatment assignment by a third party but expanding beyond this creates complications. We argue that grouping study designs with labels like 'natural experiments’ or 'quasi-experiments’ provides potentially misleading guidance for causal inference given the difficulty of justifying the core assumption of ‘as-if randomisation’ across diverse designs. Rather than relying on vague labels, researchers should explicitly state their design and defend the credibility of assumptions needed for causal inference. Expansive definitions of ‘natural experiments’ can potentially bias evidence synthesis by obscuring the rigorous justifications needed for causal inference, ultimately creating more confusion than clarity.

Background: Large-scale residential energy transitions from solid fuel to clean energy are promising strategies to mitigate climate change and improve population health, but rigorous evaluation of their impacts is rare. We evaluated the impact of China’s Clean Heating Policy (CHP), which aimed to transition tens of millions of households from coal to electric and gas-based space heating, on blood pressure (BP). Methods: In winter 2018-19, we enrolled 1,003 adults aged >40 years from 50 Beijing villages not yet enrolled in the CHP; 20 villages were treated during follow-up (winters 2019-20 and 2021-22). Brachial and central BP and covariates were measured during household visits by trained staff. Policy impacts were estimated using an extended two-way fixed-effects difference-in-differences approach with village-clustered standard errors and adjustment for key BP predictors to improve precision. Findings: We found evidence of reductions (in mmHg) in brachial systolic BP (-1.4, 95% confidence interval [CI]: -3.3, 0.5), central systolic BP (-1.5, 95%CI: -3.3, 0.4), brachial diastolic BP (-1.6, 95%CI: -2.9, -0.3), and central diastolic BP (-1.6, 95%CI: -2.9, -0.3). Treatment effects varied by the year of policy enrollment (p for homogeneity = 0.00 to 0.14) with greater BP reductions among participants in earlier-treated villages. Interpretation: Household energy policies like the CHP may serve as effective population-level interventions to reduce BP in China and complement high-risk approaches to BP reduction.

RATIONALE:Northern China's Clean Heating Policy (CHP) aimed to reduce wintertime coal burning in rural homes by restricting coal use and providing subsidies for clean heating. The policy's health impacts on respiratory outcomes have not been empirically evaluated. OBJECTIVES:To estimate the impact of the CHP on respiratory symptoms and airway inflammation using a difference-in-differences design leveraging the policy's staggered rollout across rural Beijing villages. METHODS:We enrolled 1003 adults aged ≥40 years from 50 rural villages reliant on coal heating at baseline (2018-2019). Over 4 winters (2018-2022), 20 villages were enrolled in the CHP. During up to 3 winter waves of data collection, we measured respiratory symptoms by questionnaire and, in a subsample, measured fractional exhaled nitric oxide (FeNO). We estimated the policy's effects using extended 2-way fixed effects models, accounting for village-level clustering and potential time-varying confounders. MEASUREMENTS AND MAIN RESULTS:Exposure to the CHP was associated with a 7.5 percentage point reduction (95% confidence interval (CI): -12.8, -2.3) in the prevalence of any respiratory symptom, primarily driven by reductions in reported difficulty breathing (-3.3 pp, 95% CI: -8.0, 1.3), shortness of breath (-3.5 pp, 95% CI: -9.3, 2.3), and cough (-2.8 pp, 95% CI: -7.3, 1.6). We observed no evidence of an effect of the CHP on FeNO (0.3 ppb, 95% CI: -2.2, 2.8). CONCLUSIONS:The CHP led to reductions in reported respiratory symptoms among Beijing adults. This study contributes to the limited empirical evidence that clean energy policies can yield health benefits.

Abstract Background: Despite primary care's role in hepatitis C elimination, evidence of primary care providers’ involvement remains limited. To enhance our knowledge of health care use among hepatitis C–infected individuals, we described trends in hepatitis-related visits and patients’ characteristics by provider specialty in Quebec. Methods: We conducted a population-based cohort study using all hepatitis C cases in the Quebec Mandatory Reportable Disease database (1990–2018), linked with the provincial physician billing database. We described monthly rates of hepatitis-related medical visits using a generalized additive model across different provider specialties and stratified our results by at-risk populations. Results: Between 1990 and 2018, 37,251 patients were diagnosed with hepatitis C. Visit rates were lower for other specialties compared to gastroenterologists; rate ratios (RRs) were 0.73 (95% CI 0.67–0.79) for general practitioners/family physicians (GPs/FPs) and 0.24 (95% CI 0.21–0.26) for internal medicine physicians. The RR for GPs/FPs was 1.21(95% CI 1.05–1.39) among people who inject drugs (PWID), 0.76 (95% CI 0.71–0.82) among the 1945–1975 birth cohort, and 0.37 (95% CI 0.28–0.49) among immigrants, compared to gastroenterologists. Patients seen primarily by GPs/FPs were more likely to have a history of drug use and mental health disorders than those seen by specialists. Conclusions: Hepatitis C cases were more likely to be seen by gastroenterologists than by GPs/FPs in Quebec from 1990 to 2018. However, GPs/FPs had higher visit rates for PWID. Specialists more often managed immigrants and the 1945–1975 cohort. These findings suggest disparities in care access and emphasize GPs/FPs’ role in managing hepatitis C among marginalized populations.

Pursuing replicability - independent evidence for previous claims - is important for creating generalizable knowledge(1,2). Here we attempted replications of 274 claims of positive results from 164 quantitative papers published from 2009 to 2018 in 54 journals in the social and behavioural sciences. Replications were high powered on average to detect the original effect size (median of 99.6%), used original materials when relevant and available, and were peer reviewed in advance through a standardized internal protocol. Replications showed statistically significant results in the original pattern for 151 of 274 claims (55.1% (95% confidence interval (CI) 49.2-60.9%)) and for 80.8 of 164 papers (49.3% (95% CI 43.8-54.7%)), weighed for replicating multiple claims per paper. We observed modest variation in replication rates across disciplines (42.5-63.1%), although some estimates had high uncertainty. The median Pearson's r effect size was 0.25 (95% CI 0.21-0.27) for original studies and 0.10 (95% CI 0.09-0.13) for replication studies, an 82.4% (95% CI 67.8-88.2%) reduction in shared variance. Thirteen methods for evaluating replication success provided estimates ranging from 28.6% to 74.8% (median of 49.3%). Some decline in effect size and significance is expected based on power to detect original effects and regression to the mean because we replicated only positive results. We observe that challenges for replicability extend across social-behavioural sciences, illustrating the importance of identifying conditions that promote or inhibit replicability(3,4).

PURPOSE:To improve the identification of cerebral palsy cases in administrative health data. METHODS:We included all children in a population-based cerebral palsy registry in Quebec, Canada, born from 1999 through 2002, and a sample of children without cerebral palsy. Population-based hospitalization and physician billing records through 2012 were obtained for all children. We used logistic regression to model the probability of cerebral palsy, using International Classification of Diseases codes for related diseases. We reported receiver operating characteristic (ROC) and precision-recall (PR) curves, and compared the accuracy to that of existing algorithms. We also reported the accuracy of cerebral palsy codes by age, data source, and gestational age at birth. RESULTS:The area under the ROC and PR curves of our model were 0.98 (95 % CI: 0.97-0.99) and 0.73 (95 % CI: 0.63-0.79), respectively. Cut-offs with a similar specificity to existing algorithms yielded sensitivities that were 1-14 %age-points higher. The sensitivity of cerebral palsy codes was higher (and the specificity was lower) with longer follow-up times since birth, when using both hospitalization and billing records, and among children born preterm. CONCLUSIONS:Our model improved identification of cerebral palsy cases in administrative data, but residual misclassification remained.

Gastroesophageal reflux disease (GERD) affects 6.8 million individuals in Spain, incurring €56 million/year in healthcare costs. Standard-of-care treatment (SOC) in Spain includes medical management with proton pump inhibitors (PPIs) and laparoscopic Nissen fundoplication (LNF) in selected cases. The limitations of PPIs, including high rates of unresponsiveness, adverse events (AEs) associated with long-term use, and nonindicative misuse, increase the economic strain on European healthcare systems. The durability of LNF treatment is hindered by reoperation and postoperative complications. RefluxStop, a novel implantable device, restores the anti-reflux barrier without encircling the esophagus and confers long-term efficacy and safety in the treatment of GERD. This study assessed the cost-effectiveness of RefluxStop compared with medical (PPI-based) and surgical (LNF) SOC for refractory GERD in Spain. The cost-effectiveness of RefluxStop versus PPI-based medical management and LNF was assessed from the Spanish National Health System (SNS) perspective over a lifetime horizon (monthly cycles, 3.0

BACKGROUND:Few studies have assessed the impact of large-scale early childhood education and care (ECEC) programmes. In this study, we evaluated the impact of national-level policy changes providing access to free ECEC during children's preschool years on symptoms of mental distress during early adolescence. METHODS:We used data from nine European countries that participated in five waves of the Health Behaviour in School-aged Children (HBSC) Study conducted between 2002 and 2018, including 165 656 participants who were born between 1988 and 2003, and surveyed when they were 11-15 years old. Primary outcomes were feeling low, feeling irritable, feeling nervous and having difficulty sleeping more than once per week in the past 6 months. Our difference-in-differences design compared outcomes across birth cohorts in five treated countries that expanded access to free ECEC to changes in control countries that did not. We examined heterogeneity by gender and family affluence. RESULTS:One year of access to free ECEC reduced the prevalence of feeling low by 1.3 percentage-points (95% CI 2.5 to -0.1), feeling irritable by 2.1 percentage-points (95% CI -4.0 to -0.3) and feeling nervous by 1.8 percentage-points (95% CI -2.7 to -0.9) and did not appreciably affect the prevalence of having difficulty sleeping. We did not observe evidence of a marked beneficial effect across all treated countries, and stratified analyses did not show heterogeneity in these associations by gender or family affluence. Our main results were robust to alternative control groups. CONCLUSION:Our findings suggest that the effects of free ECEC policies on adolescent mental health are context-specific.

Background: Living with children has been associated with greater risks of SARS-CoV-2 infection, COVID-19 hospitalisation, and COVID-19 death. We examined how these associations varied during 2021–22 and according to the COVID-19 vaccination status of adults. Methods: We carried out a population-based cohort study, with the approval of NHS England. Primary care data and pseudonymously-linked hospital and death records from England, between 20th December 2020 and 21st February 2022, were used for adults (≥18 years) registered at a general practice on 20th December 2020. Adjusted hazard ratios (HRs) for SARS-CoV-2 infection, COVID-19 hospitalisation, or COVID-19 death, by presence of children in the household were calculated. Results: The cohort included 9,417,278 adults aged ≤65 years and 2,866,602 adults aged >65 years. Adults aged ≤65 years living with children of any age (versus no children) had greater risks of SARS-CoV-2 infection and COVID-19 hospitalisation (but not COVID-19 death), both when schools were open and closed (e.g. HR=1.50, 95% CI:1.49-1.51, for SARS-CoV-2 infection in the ‘Omicron dominant’ period, when schools were open, in adults living with children aged 0–11 years only). These associations also existed for adults aged >65 years, and there was some evidence that adults living with children also had greater risks of COVID-19 death. Vaccinated adults living with children had greater risks of SARS-CoV-2 infection, but lower risks of COVID-19 hospitalisation and death, than unvaccinated adults not living with children. Conclusions: In an era of widespread adult vaccination, adults living with children remained at increased risk of SARS-CoV-2 infection and COVID-19 hospitalisation.

Policy Points The liberalization of medical and recreational cannabis policies may increase cannabis initiation across age groups, with increased prevalence of cannabis use among young adults and adults and weaker effects among youth. Evidence also suggests increases in cannabis-related health care utilization among adults. Alcohol use may decrease following medical legalization (suggesting use of cannabis in place of alcohol), but it may increase among young adults following recreational legalization (suggesting co-consumption). Evidence suggests a potential decrease in tobacco use across age groups and cannabis policy changes, and most studies found no change or a decrease in opioid-related outcomes, although evidence was less consistent for opioid-related mortality specifically. CONTEXT:Substantial changes in cannabis policies are occurring globally; however, the impacts of these reforms on cannabis use, as well as downstream effects on other substance use, remain unclear. METHODS:We conducted a systematic review to identify studies examining the impact of a cannabis policy change on substance use. We searched Embase, Medline, PsycINFO, the Web of Science Core Collection, and the Criminal Justice Database, as well as gray literature sources including the Social Science Research Network. The included studies employed a quasi-experimental approach and were assessed for risk of bias using a modified version of ROBINS-I to facilitate the assessment of these designs. The findings were synthesized using a descriptive, analytical approach. FINDINGS:The included reports (N = 176) were published between 1993 and 2024, with approximately two-thirds published after 2019. Most were peer-reviewed publications (n = 148) applying a difference-in-differences (n = 129) or interrupted time series (n = 42) approach to data from the United States (n = 141). Medical and recreational cannabis legalization may increase cannabis initiation across age groups, with increased prevalence of cannabis use among young adults and adults and inconsistent evidence among youth. The impacts on alcohol use were differential by policy and age group, with potential decreases following medical legalization and potential increases following recreational legalization among young adults. Evidence from a limited number of studies suggested potential decreases in tobacco use among all age groups. Most studies found no change or a decrease in opioid-related outcomes, although evidence was less consistent for opioid-related mortality. We found few studies examining cannabis decriminalization, with no clear evidence of changes in cannabis or other substance use. CONCLUSIONS:Overall, these findings suggest that medical and recreational legalization increase cannabis use, with weaker effects among youth. In addition, potential substitution effects were identified for other substances (e.g., alcohol, tobacco, opioids), excepting complementary alcohol use among young adults following recreational cannabis legalization.

Abstract Large-scale residential energy transitions from solid fuel to clean energy are promising strategies to mitigate climate change and improve population health, but rigorous evaluation of their impacts is rare. China’s Clean Heating Policy (CHP) aimed to transition tens of millions of households from coal to electric and gas-based space heating. Following evidence of policy-driven improvements in indoor air pollution and indoor temperature, we evaluated the CHP’s impact on blood pressure (BP). In winter 2018–2019, we enrolled 1,003 adults aged >40 years from 50 Beijing villages not yet treated by the CHP; 20 villages were treated during follow-up (winters 2019–2020 and 2021–2022). Brachial and central BP and covariates were measured during household visits by trained staff. Policy impacts were estimated using an extended two-way fixed-effects difference-in-differences approach with village-clustered standard errors and adjustment for key BP predictors to improve precision. We found evidence of reductions (in mmHg) in brachial systolic BP (−1.4, 95% confidence interval [CI]: −3.3, 0.5), central systolic BP (−1.5, 95% CI: −3.3, 0.4), brachial diastolic BP (−1.6, 95% CI: −2.9, −0.3), and central diastolic BP (−1.6, 95% CI: −2.9, −0.3) among villages treated by the CHP compared with those untreated. Treatment effects varied by the year villages were treated by the CHP (p for homogeneity = 0.00 to 0.14) with greater BP reductions among participants in earlier-treated villages. Household energy policies like the CHP may serve as effective population-level interventions to reduce BP in China and complement high-risk cardiovascular prevention strategies.

OBJECTIVE:To use a natural experiment to investigate the effect of antenatal corticosteroids on the risk of cerebral palsy. STUDY DESIGN:We included singleton livebirths with a maternal admission for delivery from 31 + 0 through 36 + 6 weeks of gestation, in British Columbia, Canada, between 2000 and 2015. Guidelines recommended antenatal corticosteroids through 33 + 6 weeks, and we estimated the effect of the corresponding sharp drop in the proportion treated at 34 + 0 weeks on the risk of a composite of death before age 2 or cerebral palsy. We defined cerebral palsy using diagnostic codes in hospital and physician-billing records before age 5 years and corrected for misclassification using external estimates of the sensitivity and specificity. We used logistic regression to estimate marginal effects at 34 + 0 weeks. RESULTS:There were 20 009 children in our study sample. The crude and misclassification-corrected risks of cerebral palsy were 6.2 and 5.6 per 1000, respectively. The risk of death before age 2 or cerebral palsy declined with increasing gestational age at maternal admission for delivery, but we found no convincing evidence of an abrupt change just before vs just after 34 + 0 weeks (risk ratio: 0.98, 95% confidence interval: 0.50 to 1.98). Results were similar using a composite outcome of in-hospital newborn death or cerebral palsy, and using cerebral palsy alone. CONCLUSIONS:We did not find evidence that the lower likelihood of being treated with antenatal corticosteroid at 34 + 0 weeks affected the risk of cerebral palsy, but the estimates were imprecise and compatible with benefits or harms.

Mental disorders are associated with elevated mortality rates and reduced life expectancy. However, it is unclear whether these associations differ by socioeconomic position (SEP). The aim of this study was to explore comprehensively the role of individual‐level SEP in the associations between specific types of mental disorders and mortality (due to all causes, and to natural or external causes), presenting both relative and absolute measures. This was a cohort study including all residents in Denmark on January 1, 2000, following them up until December 31, 2020. Information on mental disorders, SEP (income percentile, categorized into low, <20%; medium, 20‐79%; and high, ≥80%), and mortality was obtained from nationwide registers. We computed the average reduction in life expectancy for those with mental disorders, relative and absolute differences in mortality rates, and proportional attributable fractions. Subgroup analyses by sex and age groups were performed. Overall, 5,316,626 individuals (2,689,749 females and 2,626,877 males) were followed up for 95.2 million person‐years. People with mental disorders had a shorter average life expectancy than the general population regardless of SEP (70.9‐77.0 vs. 77.2‐85.1 years, depending on income percentile). Among individuals with a mental disorder, the subgroup in the top 3% of the income distribution had the longest average life expectancy (77.0 years), and this estimate was lower than the shortest life expectancy in the general Danish population (77.2 years for individuals in the bottom 6% income distribution). The mortality rate differences were larger in the low‐income than the high‐income group (19.6 vs. 13.3 per 1,000 person‐years). For natural causes of death, a socioeconomic gradient for differences in life expectancy and mortality rates was observed across most diagnoses, both sexes, and all age groups. For external causes, no such gradient was observed. In the low‐SEP group, 10.1% of all deaths and 23.7% of those related to external causes were attributable to mental disorders, compared with 3.5% and 8.7% in the high‐SEP group. Thus, our data indicate that people with mental disorders have a shorter life expectancy even than people with the lowest SEP in the general population. The socioeconomic gradients in mortality rates due to natural causes highlight a greater need for coordinated care of physical diseases in people with mental disorders and low SEP.

OBJECTIVES:Loneliness is highly prevalent and can have severe health consequences. While generally assumed to increase with age, some evidence suggests the relationship between age and loneliness may vary across country. In this study, we investigate the contribution of demographic and health factors to age-related inequalities in loneliness both within and across countries. METHOD:We used population-based cross-sectional data from 64,324 older adults (age range: 50-90 years) across 29 countries. Loneliness was measured with the 3 item UCLA loneliness scale. We quantified the magnitude of age inequalities in loneliness using concentration indices, and we estimated the contribution of demographic and health factors to age inequalities in loneliness using a decomposition approach. RESULTS:Loneliness was generally more concentrated among the oldest adults in the sample, although in the US and the Netherlands it was more concentrated among younger adults. Top contributors to age inequalities in loneliness were being unmarried and not working; however, the amount that factors contributed to inequalities differed markedly by country. CONCLUSION:Age inequalities in loneliness, and contributors to these inequalities, vary substantially across countries, suggesting that loneliness is not an inevitable consequence of age but may instead be shaped by environments within countries (e.g. social cohesion).

Background: Outdoor and household PM2.5 are established risk factors for chronic disease and early mortality. In China, high levels of outdoor PM2.5 and solid fuel use for cooking and heating, especially in winter, pose large health risks to the country’s aging population. Hand grip strength is a validated biomarker of functional aging and strong predictor of disability and mortality in older adults. We investigated the effects of wintertime household and outdoor PM2.5 on maximum grip strength in a rural cohort in Beijing. Methods: We analyzed data from 877 adults (mean age: 62 y) residing in 50 rural villages over three winter seasons (2018–2019, 2019–2020, and 2021–2022). Outdoor PM2.5 was continuously measured in all villages, and household (indoor) PM2.5 was monitored for at least two months in a randomly selected ~30% subsample of homes. Missing data were handled using multiple imputation. We applied multivariable mixed effects regression models to estimate within- and between-individual effects of PM2.5 on grip strength, adjusting for demographic, behavioral, and health-related covariates. Results: Wintertime household and outdoor PM2.5 concentrations ranged from 3 to 431 μg/m3 (mean = 80 μg/m3) and 8 to 100 μg/m3 (mean = 49 μg/m3), respectively. The effect of a 10 μg/m3 within-individual increase in household and outdoor PM2.5 on maximum grip strength was 0.06 kg (95%CI: −0.01, 0.12 kg) and 1.51 kg (95%CI: 1.35, 1.68 kg), respectively. The household PM2.5 effect attenuated after adjusting for outdoor PM2.5, while outdoor PM2.5 effects remained robust across sensitivity analyses. We found little evidence of between-individual effects. Conclusions: We did not find strong evidence of an adverse effect of household PM2.5 on grip strength. The unexpected positive effects of outdoor PM2.5 on grip strength may reflect transient physiological changes following short-term exposure. However, these findings should not be interpreted as evidence of protective effects of air pollution on aging. Rather, they highlight the complexity of air pollution’s health impacts and the value of longitudinal data in capturing time-sensitive effects. Further research is needed to better understand these patterns and their implications in high-exposure settings.

BACKGROUND:In contrast to other observational study designs, quasi-experimental approaches (eg, difference-in-differences, interrupted time series, regression discontinuity, instrumental variable, synthetic control) account for some sources of unmeasured confounding and can estimate causal effects under weaker assumptions. Studies which apply quasi-experimental approaches have increased in popularity in recent decades, therefore investigators conducting systematic reviews of observational studies, particularly in biomedical, public health, or epidemiologic content areas, must be prepared to encounter and appropriately assess these approaches. OBJECTIVE:Our objective is to describe key methodological challenges and considerations for systematic reviews including quasi-experimental studies, with attention to current recommendations and approaches which have been applied in previous reviews. CONCLUSION:Recommendations for authors of systematic reviews: We recommend that individuals conducting systematic reviews including quasi-experimental studies: (1) search a broad range of bibliographic databases and gray literature, including preprint repositories; (2) do not use search strategies which require specific terms for study design for identification, given inconsistent nomenclature and poor database indexing for quasi-experimental studies; (3) ensure that their review team includes several individuals with expertise in quasi-experimental designs for screening and risk of bias assessment in duplicate; (4) use an approach to risk of bias assessment which is sufficiently granular to identify studies most likely to report unbiased estimates of causal effects (eg, modified Risk Of Bias In Nonrandomized Studies - of Interventions); and (5) consider the implications of varied estimands when interpreting estimates from different quasi-experimental designs. Researchers may also consider restricting systematic review inclusion to quasi-experimental studies for feasibility when addressing research questions with large bodies of literature. However, a more inclusive approach is preferred, as well-designed studies using a variety of methodological approaches may be more credible than a quasi-experiment which violates causal assumptions. Recommendations for the research community: Many of the challenges faced in conducting systematic reviews of quasi-experimental studies would be ameliorated by improved consistency in nomenclature, as well as greater transparency from authors in describing their research designs. The broader community (eg, research networks, journals) should consider the creation and implementation of reporting standards and protocol registration for quasi-experimental studies to improve study identification in systematic reviews.

China's Clean Heating Policy (CHP), aimed at shifting households from coal to electricity for space heating, represents a major residential energy transition initiative. We evaluated its multi-year impacts on outdoor, indoor, and personal exposures to PM2.5 and black carbon (BC) across 50 villages and 1,236 households in rural Beijing. Using a difference-in-differences (DiD) design, we observed a substantial (31 μg/m3) reduction in winter (3 month) indoor PM2.5 (95% CI: -53, -9), but an increase in 24-h indoor BC by 2.6 (0.4, 4.7) μg/m3. CHP-driven reductions in personal exposures were limited, emphasizing the limitations of using single 24-h measurements to estimate "usual" exposure. Outdoor air quality improved in all villages, with no difference between treated versus untreated villages. Exposure-energy trade-off analysis showed that untreated households achieved similar personal PM2.5 reductions at lower cost, with smaller coal use reductions and less electricity expenditures. The CHP significantly reduced seasonal indoor PM2.5, but continued burning of biomass, which was accessible at no cost, limited air quality improvements and may have contributed to the observed increase in 24-h indoor BC. This illustrates how behavioral choices, economic feasibility, and selection of exposure metrics influence the measured impact of household energy transitions.

Chronic exposure to volatile organic compounds (VOCs) poses significant health risks, especially in rural households with prolonged winter occupancy and diverse emission sources. This study investigates the key influencing factors of indoor VOCs complexities in rural Beijing through an integrated analysis of environmental conditions, behavioral patterns, and energy consumption frameworks. Analyzing 320 air samples from 192 randomly selected households, we reveal that indoor VOC concentrations were significantly higher than outdoor levels, with C3-C4 alkanes/alkenes constituting the dominant fraction (62.1 %). A critical finding identifies liquefied petroleum gas (LPG) cooking as a significant contributor to indoor VOC burdens. Contrary to conventional assumptions, heating fuel type (coal, biomass, or clean energy) exhibited negligible influence on VOC levels, attributable to spatial configurations of combustion infrastructure: 90 % of coal-heated households utilized radiator systems that isolated stoves from living spaces, while biomass units were predominantly outdooroperated, mitigating direct indoor emissions. Among all variables, CO2 concentration demonstrated the strongest statistical association with VOCs, showing significant correlations across all seven VOC categories. Elevated aromatic hydrocarbons and oxygenated VOCs (OVOCs) in smoking households underscore tobacco smoke as a persistent indoor pollutant source. These findings challenge energy transition narratives by emphasizing that spatial design of heating systems, rather than fuel type alone, critically governs indoor air quality.