Natural Experiments Research Articles

The high-pressure, vacancy-stabilized component in clinopyroxenes

Abstract Motivated by the recent discovery of albitic clinopyroxene, we assess the molar volume systematics of vacancy-stabilized, high-pressure clinopyroxenes. Previous assessments used the Ca-Eskola component (Ca0.5□0.5)M2AlM1Si2TO6 (where the empty rectangle symbol denotes a vacancy) as an end-member and were limited to compositions with ≤ 50% vacancies in the M2 site. The discovery of albitic jadeite calls for extension of the solid solution space towards an end member with entirely vacant M2 sites, □M2SiM1Si2TO6, i.e. silica in the C2/c pyroxene structure. Based on our new and compiled data, we fit a model for volumes of clinopyroxenes in an 11-component subsystem. We tested two different scenarios: ideal mixing and symmetric excess volumes. Ideal mixing is easily rejected, as the correlation between vacancy concentration and volume at standard conditions is clearly nonlinear. The symmetric excess volume model, however, yields an adequate fit to the data when using 3 excess terms (Hd-En, Hd-Di, and Hd-Jd). The estimated molar volume of the clinopyroxene-structured silica end member, which has one octahedrally-coordinated silicon atom per formula unit, is 60.77 ± 0.75 cm3/mol on a six-oxygen formula basis, slightly smaller than that of coesite (61.73 cm3/mol) but much larger than that of stishovite (41.44 cm3/mol). We also obtained a molar volume of 62.16 ± 0.75 cm3/mol for the Ca-Eskola component, modestly larger than earlier estimates extrapolated with an ideal mixing assumption from natural samples (60.52 ± 0.73 cm3/mol) or experiments (60.87 ± 0.63 cm3/mol). The proposed volume model provides a partial basis for assessing the formation conditions of vacancy-stabilized pyroxenes.

Worse Weather Amplifies Social Media Activity.

Humanity spends an increasing proportion of its time interacting online, yet-given the importance of social media to human welfare-the external factors that regularly shape online behavior remain markedly understudied. Do environmental factors alter rates of online social activity? We conducted two large natural experiments to investigate how worse weather conditions affect social-media use in the United States, analyzing over 3.5 billion posts from Facebook and Twitter (now X) between 2009 and 2016. We found that extreme temperatures and added precipitation each independently amplified social-media activity, effects that persisted within individuals. Compounded weather extremes produced markedly larger increases in social-media activity. Days colder than -5 °C with 1.5 to 2 cm of precipitation elevated social-media activity by 35%, nearly triple the surge seen on New Year's Eve in New York City. Our study highlights that environmental conditions play a critical-but overlooked-role in shaping digital social interaction.

The convergent evolution of hummingbird pollination results in repeated floral scent loss through gene downregulation.

The repeated evolution of the same trait in different lineages provides powerful natural experiments to study the phenotypic and genotypic predictability of trait gain and loss. A fascinating example is the repeated evolution of hummingbird pollination in plant lineages in the Americas, a widespread and often unidirectional phenomenon. The spiral gingers in the genus Costus are ancestrally bee-pollinated, and hummingbird pollination has evolved multiple times independently in the tropical Americas. These pollinator transitions are accompanied by predictable morphological and color changes, but the changes in floral scent have not been described. In this study, we describe the floral scent composition of 30 species of Costus sampled across the phylogeny to understand how floral scent has evolved across the genus with respect to pollinator transitions. We then combine transcriptomics and genomics to identify genetic expression differences and gene family evolution associated with pollinator transitions. We show that hummingbird-pollinated species have mostly lost their floral scent, whereas bee-pollinated species exhibit either floral scent maintenance or in some cases, gains of more diverse scent profiles. We find the floral scent loss appears to be due to gene downregulation rather than pseudogenization. The remarkable consistency of scent loss in hummingbird-pollinated species highlights the shared strong selection pressures experienced by these lineages. Even species with more recent transitions from bee to hummingbird pollination exhibit scent loss, highlighting the rapid breakdown of scent emission following pollinator transitions. This research highlights the capacity for rapid changes when selection pressures are strong through downregulation of floral scent genes.

Evaluating the impact of Canadian cannabis legalization on cannabis use outcomes in emerging adults: Comparisons to a US control sample via a natural experiment.

Recreational cannabis legalization marked a significant policy shift in Canada, but has been difficult to evaluate because of the absence of a control group. Although it is unfeasible to evaluate legalization using a randomized controlled trial design, sophisticated statistical techniques can employ quasi-experimental designs using natural experiments. This study evaluates the impact of cannabis legalization in a longitudinal cohort of Canadian emerging adults by comparing changes in cannabis use frequency and related consequences over time to changes in a similar cohort in a United States jurisdiction where no policy change took place. Two samples of emerging adults from Hamilton, Ontario, and Memphis, Tennessee, were followed longitudinally in 4-month intervals from March 16, 2018 to March 11, 2020, with three pre-legalization and four post-legalization assessments. Doubly robust difference-in-difference (DiD) estimation was used to assess whether cannabis legalization impacted cannabis use frequency or cannabis-related consequences in the Canadian sample over time. The impact of cannabis legalization on alcohol use and alcohol-related consequences was also assessed as a control form of substance use for which no policy change took place. Cohort differences were adjusted within DiD estimation using propensity score balancing. Against a general trend of decreasing use over time, the DiD estimation revealed significantly greater cannabis use frequency approximately 6-months post legalization (ATT (95% CI): 0.2245 (0.0154, 0.4336)) and approximately one year post legalization (ATT (95% CI):0.3091 (0.0473, 0.5709)) in the Canadian sample compared to the American sample. Cannabis-related consequences were also greater in the Canadian sample at both of these time points (ATT (95% CI): 0.0.7610 (0.0797, 1.4423)), (ATT (95% CI): 1.0396 (0.1864, 1.8928)). These higher levels reflected less steep declines over time (i.e., attenuated 'aging out'). Alcohol changes showed no impact of legalization at any time point, as expected. Findings suggest that cannabis legalization was associated with smaller reductions in cannabis use frequency and adverse consequences than expected in the Canadian sample compared to the American control sample. Although the magnitude of these impacts was small, these findings suggest the start of diverging cannabis trajectories. Given that effects of legalization are hypothesized to be long-term rather than immediate, further monitoring of the impacts of cannabis legalization on developmental trends in cannabis use and related consequences is warranted.

Influence mechanism of AC electric field on rime ice accretion on the insulator and its experimental verification in the natural environment

Insulator icing can easily trigger flashover trips in heavily ice-covered areas, and analyzing the formation mechanism of ice accumulation on the insulator is essential for predicting its flashover development. To accurately dissect the process of insulator icing, a coupled mathematical model of the flow field and electric field, as well as a droplet motion model were elaborated in this paper based on the principles of fluid mechanics and electromagnetic field. Subsequently, the characteristics of droplet motion deviation and its physical collision process with an insulator surface under AC electric field were investigated. The results demonstrate that the charged droplets tend to oscillate along the electric field lines in AC electric field, and the amplitude of the oscillation increases with the applied voltage increasing. Moreover, the number of droplets captured by the insulator rises with the increase of voltage, wind speed, and median volume diameter of the droplet. Combined with the simulation and natural icing experiments, it is observed that ice branches grow in the direction of electric field force, and as the voltage rises, ice branches gradually spread from the edge of the shed to its surface, increasing surface roughness. The density of ice exhibits an inverted U-shaped relationship as the electric field strength increases. Ice mass and ice length present nonlinear growth with an increase in icing time. Furthermore, compared with that without energization, the icing amount and icing length increase by more than 13 % under AC voltage of 40 kV.

Covid-19 Pandemic as a Natural Experiment: The Case of Home Advantage in Sports

Establishing a causal relationship requires not only the presence of a factor of interest but also the demonstration that the relationship is absent when the factor is absent. Such ideal conditions are rare, especially in observational studies in which creating control conditions is inherently difficult. The COVID-19 pandemic, with its unparalleled disruptions, offers a unique opportunity to isolate causal effects and test previously impossible hypotheses. Here, we examine the home advantage (HA) in sports—a phenomenon in which teams generally perform better in front of their home fans—and how the pandemic-induced absence of fans offered a fortunate yet systematic change to typical conditions, serving as a natural experiment. Using a structural equation modeling approach and building a mediation model encompassing all relevant HA factors, we quantified the reduction in HA and elucidated the specific mechanisms behind it. The theory behind HA and the availability of measures for each factor before and during COVID-19 lockdowns enabled us to estimate all postulated pathways within a natural experimental context. The robust statistical framework used in our study offers a foundational model for integrating naturally occurring events that serve as control conditions into the analysis of various real-life phenomena.

Physical activity-the past, present and potential future: a state-of-the-art review.

This is a state-of-the-art review of historical developments, current approaches and recommended future directions in physical activity (PA) research, practice and policy. Since the early epidemiological studies in the 1950s, PA research has developed from within a biomedical paradigm. There is now a strong evidence base linking PA with positive health outcomes. PA is currently understood as a multi-sector issue, requiring a multi-sector solution (e.g. transport, urban design, sport), resulting in multiple individual and societal benefits (e.g. addresses multiple Sustainable Development Goals), however, there is a disconnect between interventions, policy and practice. This may be due to limited cross-sector collaboration between, and within, the public and private sectors. Furthermore, the mix of policy instruments employed by governments to implement PA policy to date has been dominated by soft (e.g. communication) rather than hard options (e.g. fiscal). To progress in PA promotion, we need to move beyond health outcome and intervention evidence generation (e.g. focus on testing efficacy in highly controlled settings), to more complex, real world, politically informed, multi-sector, scale-up and policies, while concurrently collecting data to evaluate such efforts (e.g. natural experiments and evaluations of the policy process). PA programs may benefit from greater incorporation of public policy considerations, so that proposed interventions and policies are designed with potential political constraints in mind. We conclude by providing a call to action to advance the understanding of the role of politics in PA, in order to develop politically informed action on PA.

Editorial: Sports, economics, and natural experiments: advances and retrospection

Editorial: Sports, economics, and natural experiments: advances and retrospection

Flood-driven survival and growth of dominant C4 grasses helps set their distributions along tallgrass prairie moisture gradients.

Five C4 grasses (Bouteloua curtipendula, Schizachyrium scoparium, Andropogon gerardii, Sorghastrum nutans, Spartina pectinata) dominate different portions of a moisture gradient from dry to wet tallgrass prairies in the Upper Midwest of the United States. We hypothesized that their distributions may partly reflect differences in flooding tolerance and context-specific growth relative to each other. We tested these ideas with greenhouse flooding and drought experiments, outdoor mesocosm experiments, and a natural experiment involving a month-long flood in two wet-mesic prairies. Bouteloua promptly succumbed to inundation, so flooding intolerance likely excludes it from wet and wet-mesic prairies. Competition is likely to exclude short-statured Bouteloua from productive mesic sites. Schizachyrium is excluded from wet prairies by low flooding tolerance, demonstrated by all experiments. Sorghastrum had low flooding tolerance in both greenhouse and natural experiments, suggesting that physiological intolerance excludes it from wet prairies. Spartina had by far the greatest growth under the wettest mesocosm conditions; this and comparisons of species growth in monocultures vs. mixtures suggests that competition helps it dominate wet prairies. Indeed, quadrat presence of Spartina increased by 57% two years after flooding of two prairies, while that of upland grasses declined by 44%. The high flooding tolerance, lack of significant differences from other species in drought tolerance, and tall stature of Andropogon suggest that broad physiological tolerance combined with competitive ability allows it to thrive across the prairie moisture gradient. Flooding helps shape the distributions of dominant prairie grasses, and its effects may become more important as extreme rain events continue to increase.

Distinct Functioning of Low‐ Versus High‐Altitude Refugia in the Mediterranean: Inferences From Life‐History Traits of Two Related Relict Trees From the Islands of Sicily and Crete

ABSTRACTAimRelict trees are the outcome of long‐term ‘natural experiments’. Accordingly, they provide opportunities to study the effects of local adaptation of trees, which are still poorly understood but crucial in the context of climate change. In turn, the physical settings of refugia at macro‐ and microscale are the key drivers of the environmental adaptability of such species. Using two congeneric climate relict trees (Zelkova sicula and Z. abelicea) as model species, we analysed the functional relationships between tree growth patterns and the distinctive environmental drivers of low‐ versus high‐altitude refugia in the Mediterranean.LocationMediterranean islands of Sicily (Italy) and Crete (Greece).MethodsTo evaluate the growth potential of the two relict trees we used top height and multi‐year data of shoot length over the entire distribution range of both species. Growth form and height growth dynamics of Z. sicula were also investigated by stem analysis. Moreover, tree‐ring response to climate was compared through classical dendrochronological approaches.ResultsTree size, as well as shoot and radial growth are notably greater in Z. abelicea, suggesting this species better fits in its habitat and the higher‐elevation Cretan refugia are less constraining than their low‐elevation Sicilian counterparts. Tree‐ring growth response to precipitation and evapotranspiration is rather similar between the two species and points to the key role of moisture balance on growth. However, the 1‐month delay in the response from the Sicilian to the Cretan relict mirrors the differential role of altitude against micro‐topography in decoupling from the regional climate.Main ConclusionsThe significant attenuation of environmental constraints due to the ‘elevation effect’ is a major offsetting driver for the distinct functioning of low‐ versus high‐altitude refugia in the Mediterranean, but macroclimatic patterns may locally blur the effectiveness of refugia in a long‐term conservation perspective.

Species-specific responses of canopy greenness to the extreme droughts of 2018 and 2022 for four abundant tree species in Germany.

Germany experienced extreme drought periods in 2018 and 2022, which significantly affected forests. These drought periods were natural experiments, providing valuable insights into how different tree species respond to drought. The quantification of species-specific drought responses may help to identify the most climate-change-resilient tree species, thereby informing effective forest regeneration strategies. In this study, we used remotely sensed peak-season canopy greenness as a proxy for tree vitality to estimate the drought response of four widely abundant tree species in Germany (oak, beech, spruce, and pine). We focused on two questions: (1) How were the four tree species affected by these two droughts? (2) Which environmental parameters primarily determined canopy greenness? To address these questions, we combined a recently published tree species classification map with remotely sensed canopy greenness and environmental variables related to plant available water capacity (PAWC) and atmospheric vapor pressure deficit (VPD). Our results indicate that the more isohydric species featured a greater decline in canopy greenness under these droughts compared to the more anisohydric species despite similar soil moisture conditions. Based on spatial lag models, we found that the influence of PAWC on canopy greenness increases with increasing isohydricity while the influence of VPD decreases. Our statistical analysis indicates that oak was the only species with significantly higher canopy greenness in 2022 compared to 2018. Yet, all species are likely to be susceptible to accumulated drought effects, such as insufficient recovery time and increased vulnerability to biotic pathogens, in the coming years. Our study provides critical insights into the diverse responses of different tree species to changing environments over a large environmental gradient in Central Europe and sheds light on the complex interactions between soil moisture, climate variables, and canopy greenness. These findings contribute to understanding forests' climate-change resilience and may guide forest management and conservation strategies.

Approaches in landscape fire smoke pregnancy research and the impact on offspring: A review of knowledge gaps and recommendations.

The increase in wildfires and bushfires due to climate change means that more people, including pregnant women and their fetuses will be exposed to landscape fire smoke. Although there is evidence to suggest that pregnancy landscape fire exposure is associated with lower birth weight, preterm birth and pregnancy loss, there is a lack of information on many other perinatal outcomes, as well as information on subsequent respiratory outcomes in children. Furthermore, due to the generally short term (hours/days) and intermittent nature of landscape fire smoke exposure, the knowledge to date has largely relied on natural experiments and ecological studies which can be subject to misclassification of exposure and a lack of precision. On the other hand, general urban outdoor air pollution exposure during pregnancy and subsequent perinatal and respiratory effects has been well studied. In particular, as air exposure modelling has improved so have the adaptations of methods to analyze the effects of air pollution exposure during pregnancy enabling critical windows of exposure to be identified. In this narrative review we summarize the current state of knowledge about the perinatal and respiratory effects of pregnancy landscape fire and particulate matter <2.5μm in diameter (PM2.5) air pollution exposure, including a comment on analysis methods to date, and an assessment of how methodologies used in general air pollution research in relation to pregnancy exposure can be further harnessed for landscape fire smoke exposure pregnancy research.

Assessing RELAP5 performances for the simulation of Containment Wall Condenser

Abstract The new designs of Nuclear Power Plants are increasingly emphasizing the implementation of passive systems to fulfill several safety functions. Such systems operate with low driving forces, and often employ components that require a “change state” signal for actuation. These features may lead to complete or partial actuation failures, altering the driving force conditions and consequently reducing the operational ranges and reliability of the systems themselves. However, even though the operational modes differ from those of active systems, the safety standards remain equivalent. To study these possible situations, the computer system codes must be able to simulate the phenomena related to the specific system, and they should be assessed using data both from separate and integral experimental facilities. Within the framework of the EU2020 PASTELS (Passive Systems: Simulating the Thermal hydraulics with Experimental Studies) project, a series of natural circulation experiments have been conducted in the PASI facility, an open loop Containment Wall Condenser (CWC), varying initial and boundary conditions to support the validation of system codes. As project partner, ENEA developed the PASI input deck for RELAP5/mod3.3 to assess the code’s capability in simulating complex loop components, such as the sparger, and related thermohydraulic phenomena like water flashing and geysering within the open loop. This paper presents the post-test calculations conducted with RELAP5 for test 2 (quasi-static test) and test 6 (replicating the drain phase of the water storage tank).

Exploring early Acheulian technological decision-making: A controlled experimental approach to raw material selection for percussive artifacts in Melka Wakena, Ethiopia.

The evolution of human behaviour is marked by key decision-making processes reflected in technological variability in the early archaeological record. As part of the technological system, differences in raw material quality directly affect the way that humans produce, design and use stone tools. The selection, procurement and use of various raw materials requires decision-making to evaluate multiple factors such as suitability to produce and design tools, but also the materials' efficiency and durability in performing a given task. Therefore, characterizing the physical properties of various lithic raw materials is crucial for exploring changes in human interactions with their natural environment through time and space and for understanding their technological behaviour. In this paper, we present the first step in an ongoing program designed to understand the decision-making criteria involved in the use of raw materials by the early Acheulian tool-makers at the Melka Wakena (MW) site-complex, located on the Ethiopian highlands. We present the results of the first experimental step, in which we identified and measured the engineering properties of raw materials in the lithic assemblages. These data serve as an objective, quantifiable baseline for natural experiments as well as archaeological inquiries into the technological decision-making processes of early Pleistocene hominins in Africa.

Identity Verification Standards in Welfare Programs: Experimental Evidence from India

Abstract We study the impact of reforms that introduced more stringent, biometric ID requirements into India’s largest social protection program, using large-scale randomized and natural experiments. Corruption fell but with substantial costs to legitimate beneficiaries, 1.5–2 million of whom lost access to benefits at some point during the reforms. At the same time, adverse effects appear to have been driven primarily by decisions about the way the transition was managed, illustrating both the risks of rapid reforms, and how the impacts of promising new technologies can be highly sensitive to the protocols governing their use.

The Impact of Criminal Financial Sanctions: A Multistate Analysis of Survey and Administrative Data

We estimate the impact of financial sanctions in the US criminal justice system, leveraging nine natural experiments in a regression discontinuity design framework across a diverse range of enforcement levels ($17–$6,000) and institutional environments. We leverage survey and administrative data to consider a variety of short- and long-term outcomes, including employment, recidivism, household expenditures, and other self-reported measures of well-being. We find robust evidence of precise null effects, including ruling out long-run impacts larger than −$391–$142 in annual earnings and −0.001–0.01 in annual convictions, with no corresponding payment increases despite salient and heterogeneous enforcement mechanisms. (JEL G51, H76, J31, K14, K41, K42)

Enhancing CO2 capture in cement-based materials with alkanolamines: A comprehensive study on efficiency, phase-specific impact, and carbonation mechanisms

The escalating issue of global warming, driven by the surge in CO2 emissions, necessitates innovative strategies for reducing CO2 emissions. A novel approach is explored in this study, where amines featuring a basic N atom with a lone pair are incorporated into cement paste to facilitate CO2 capture from the environment. Unlike conventional applications, the focus is on the collaborative effect of various amines on CO2 capture within diverse calcium-rich phases, encompassing portlandite and Calcium-Silicate-Hydrate (C-S-H). This investigation seeks to discern the most efficient amine and optimal concentration for CO2 capture, particularly within distinct phases of cement paste. Notably, 2-(methylamino) ethanol (MAE) demonstrates superior performance in promoting CO₂ mineralisation and has been selected to further evaluate its ability in cement paste under natural carbonation conditions. Importantly, this research presents an exhaustive analysis of C-S-H carbonation with varying Ca/Si ratios, revealing carbonation mechanisms and consequential microstructural alterations in the presence of amine. Additionally, the presence of amine significantly influences crystal growth and the polymerisation of C-S-H. Furthermore, natural carbonation experiments underscore the efficacy of MAE, showcasing a 2.5-fold increase in calcite formation in the cement paste compared to scenarios without MAE.

Beyond Russell reconstitution: A re-examination of methodologies for natural experiments

Beyond Russell reconstitution: A re-examination of methodologies for natural experiments

A maternal and child health administrative cohort in Scotland: the utility of linked administrative data for understanding early years' outcomes and inequalities

IntroductionThe early years are considered one of the most impactful points in the life course to intervene to improve population health and reduce health inequalities because, for example, both ill health and social disadvantage can track into adulthood. Scotland's outstanding systems for data linkage offer untapped potential to further our understanding of when and why inequalities in child health, development and wellbeing emerge. This understanding is vital for the consideration of policy options for their reduction. MethodsBirth registrations, hospital episodes, dispensed community prescriptions, child health reviews and immunisation records were linked for 198,483 mother-child pairs for babies born in Scotland from October 2009 to the end of March 2013, followed up until April 2018 (average age 6 years). ResultsOutcomes include birthweight and newborn health, dispensed prescriptions for mental health medications, tobacco smoke exposure, infant feeding, immunisations, hospitalisation for unintentional injuries, socio-emotional, cognitive and motor development, and overweight and obesity. Several measures are repeated throughout childhood allowing examination of timing, change and persistence. Socio-economic circumstances (SECs) include neighbourhood deprivation, relationship status of the parents, and occupational status. Descriptive analyses highlight large inequalities across all outcomes. Inequalities are greater when measured by family-level as opposed to area-level, aspects of socio-economic circumstances and for persistent or more severe outcomes. For example, 41.4% of the most disadvantaged children (living with a lone, economically inactive mother in the most deprived fifth of areas) were exposed to tobacco smoke in utero and in infancy/toddlerhood compared to &lt;1% in the least disadvantaged children (living with a married, managerial/professional mother in the least deprived quintile of areas). ConclusionThis novel linkage provides a longitudinal picture of health throughout the early years and how this varies according to family- and area-level measures of SECs. Future linkages could include other family members (e.g. siblings, grandmothers) and other sectors (e.g. education, social care). The creation of additional cohorts would allow for long-term and efficient evaluation of policies as natural experiments.

What is the relationship between hospital management practices and quality of care? A systematic review of the global evidence.

There is a widely held view that good management improves organisational performance. However, hospitals are complex organisations and the relationship between management practices and health service delivery is not straightforward. We conducted a global, systematic literature review of the quantitative evidence on the link between the adoption of management practices and quality of care in hospitals. We searched in PubMed, EMBASE, EconLit, Global Health and Web of Science on 16th October 2024, without language or country restrictions. We included empirical studies from January 1, 2000, onward, examining the quantitative association between hospital management practices and quality of care. Outcomes included structural quality (availability of resources such as drugs and equipment), clinical quality (adherence to guidelines), health outcomes and patient satisfaction or experience with care. In every study, each tested association was categorised as significantly positive (at the 5 percent level), null or significantly negative. The study was registered with PROSPERO (CRD42022301462). Of 11,731 articles, 25 studies met the inclusion criteria and had acceptable risk of bias. Studies were equally distributed between high-income and low- and middle-income countries, with 22 cross-sectional and three intervention studies. Of 111 associations, 55 (49.5%) were significantly positive, 1 (1%) was significantly negative, and 55 (49.5%) were null. Among associations tested, the majority were significantly positive for structural quality (79%), clinical quality (60%) and health outcomes (57%), while most associations between hospital management and patient satisfaction (80%) were null. The findings are mixed, with a similar proportion of positive and null associations between management practices and quality of care across studies. The evidence is limited by risk of bias introduced by non-randomised study designs. Evidence of positive associations in some settings warrants further investigation of the association through intervention studies or natural experiments. This could leverage methodological developments in quantitatively measuring management, highlighted by this review.