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Consumers' purchase decisions can be influenced by others' opinions, or word of mouth (WOM), and/or others' actions, or observational learning (OL). Although information technologies are creating increasing opportunities for firms to facilitate and manage these two types of social interaction, to date, researchers have encountered difficulty in disentangling their competing effects and have provided limited insights into how these two social influences might differ from and interact with each other. Using a unique natural experimental setting resulting from information policy shifts at the online seller Amazon.com, the authors design three longitudinal, quasi-experimental field studies to examine three issues regarding the two types of social interaction: (1) their differential impact on product sales, (2) their lifetime effects, and (3) their interaction effects. An intriguing finding is that while negative WOM is more influential than positive WOM, positive OL information significantly increases sales, but negative OL information has no effect. This suggests that reporting consumer purchase statistics can help mass-market products without hurting niche products. The results also reveal that the sales impact of OL increases with WOM volume.

Extant work shows that market actors who span multiple social categories tend to be devalued relative to their more specialized peers. Scholars typically explain this pattern of results with one of two arguments. Some contend that perceptual factors—namely, the difficulties that buyers have in making sense of category spanners—contribute to the observed pattern of devaluation. Others argue that the penalty for category-spanning stems from the fact that those who do not focus their efforts narrowly tend to offer products that are of lower quality. Because these two mechanisms often co-occur, it has been difficult to provide definitive evidence of the perceptually driven component of the multiple-category penalty. We employ a natural experiment on a peer-to-peer crowd-funding website to address this gap. Difference-in-difference analyses on matched samples show that category spanning is perceived negatively and can result in devaluation, even in the absence of underlying quality differences. This result supports the argument that perceptual issues contribute to the penalty for category spanning.

Using the before-after natural experiment occasioned by the Arab Spring in Libya, we explore how market and non-market activity affect foreign firm legitimacy in times of political turmoil. Although all MNEs in Libya had to cultivate strong ties to Qadhafi to succeed during his 40 years of rule, we found that those that also invested in social-benefit projects and in social ties with families with few ties to the Qadhafi family earned a broad-based legitimacy that helped them survive Qadhafi's overthrow. Our findings contribute to the political risk and political behavior literature the notion that the pursuit of firm legitimacy in general, and especially in the eyes of social-sector actors, is an effective hedge against political risk. More theoretically, our findings support the addition of a social-sector-based path to firm legitimacy in the host country that complements and may at times substitute for, the government-based path to foreign firm legitimacy. Practically, our findings suggest that MNEs' facing severe political risk can improve their prospects for survival by investing in relationships with influential social groups and by offering goods or services that are perceived as socially valuable.

1. Despite recent interest in linkages between above‐ and below‐ground communities and their consequences for ecosystem processes, much remains unknown about their responses to long‐term ecosystem change. We synthesize multiple lines of evidence from a long‐term ‘natural experiment’ to illustrate how ecosystem retrogression (the decline in ecosystem process rates due to long‐term absence of major disturbance) drives vegetation change, and thus above‐ground and below‐ground carbon (C) sequestration, and communities of consumer biota. 2. Our study system involves 30 islands in Swedish boreal forest that form a 5000‐year, fire‐driven retrogressive chronosequence. Here, retrogression leads to lower plant productivity and slower decomposition and a community shift from plants with traits associated with resource acquisition to those linked with resource conservation. 3. We present consistent evidence that above‐ground ecosystem C sequestration declines, while below‐ground and total C storage increases linearly for at least 5000 years following fire absence. This increase is driven primarily by changes in vegetation characteristics, impairment of decomposer organisms and absence of humus combustion. 4. Data from contrasting trophic groups show that during retrogression, biomass or abundance of plants and decomposer biota decreases, while that of above‐ground invertebrates and birds increases, due to different organisms accessing resources via distinct energy channels. Meanwhile, diversity measures of vascular plants and above‐ground (but not below‐ground) consumers respond positively to retrogression. 5. We show that taxonomic richness of plants and above‐ground consumers are positively correlated with total ecosystem C storage, suggesting that conserving old‐growth forests simultaneously maximizes biodiversity and C sequestration. However, we find little observational or experimental evidence that plant diversity is a major driver of ecosystem C storage on the islands relative to other biotic and abiotic factors. 6. Synthesis.Our study reveals that across contrasting islands differing in exposure to a key extrinsic driver (historical disturbance regime and resulting retrogression), there are coordinated responses of soil fertility, vegetation, consumer communities and ecosystem C sequestration, which all feed back to one another. It also highlights the value of well‐replicated natural experiments for tackling questions about above‐ground–below‐ground linkages over temporal and spatial scales that are otherwise unachievable.

Background Designing parks that optimise visitation and support visitors to be active is important for public health. Yet there is very little evidence about whether playground refurbishment achieves these objectives. This study examined the impact of the installation of a play-scape in a large metropolitan park in Melbourne, Australia. Methods Natural experiment study (intervention vs control). At both parks, park visitation and physical activity were assessed before (T1, 2013) and after the intervention at 12 (T2, 2014) and 24 months (T3, 2015). At each time point, measures included: observations of park visitors using the System for Observing Play and Recreation in Communities on four weekdays and four weekend days, objective monitors to record usage of the walking paths and the number of cars entering the park; and intercept surveys with adult park visitors. Cross-sectional surveys were conducted with local residents at T1 and T3. Results The observational data showed a 176% increase in park visitor counts from T1 to T2 (Incidence Rate Ratio (IRR) = 2.76, 95% CI = 1.04–7.33), at the intervention park relative to the control park. The intervention park had a 119% increase in counts of visitors observed engaging in MVPA from T1 to T2 (IRR = 2.19, 95% CI = 1.14–4.20), and a 128% increase from T1 to T3 (IRR = 2.28, 95% CI = 1.19–4.38), relative to the control park. The relative increases in visitation  at the intervention park play-scape compared with the control park playground were highly statistically significant from both T1 to T2 (IRR = 18.12, 95% CI = 5.51–59.59) and T1 to T3 (IRR = 15.05, 95% CI = 4.61–49.16). Similarly, there was a significant interaction between time and park with regard to the number of visitors observed engaging in MVPA in the play-scape/playground areas. The intercept survey data showed an increased odds of children’s regular visitation to the intervention park at T2 (OR = 2.67, 95% CI = 1.08, 6.64), compared with T1, relative to the control park. The remaining results from the intercept survey, objective monitors and resident surveys showed no significant differences in visitation between the two parks. Conclusions These findings confirm that a well-designed play-scape installation has the potential to increase park visitation and encourage visitors to be physically active. Trial registration Current controlled trial ISRCTN50745547 .

We study the effect of collaboration network structure on the contribution behavior of participating editors in Wikipedia. Collaboration in Wikipedia is organized around articles, and any two editors co-editing an article have a collaborative relationship. Based on the economic theories about network games and social role theory, we propose that an editor's position in the collaboration network influences the editor's decisions about her total contribution as well as the allocation of her efforts. By leveraging panel data collected from the Chinese language version of Wikipedia and a natural experiment resulting from blocking it in mainland China, we find strong support for the proposed effect of network position on contribution behavior. Our analysis further reveals that different aspects of an individual's network position have distinct implications. This research enhances our understanding about how collaboration network structure shapes individual behavior in online mass collaboration platforms.

Debt-ridden corporate growth and increased vulnerability was one of the causes of the 1997 financial crisis in Korea. Introduction of the outside director system has been the core part of the board reforms following the crisis. Our estimation using instruments obtained from a natural experiment illustrates that outside monitoring has (i) improved capital structure of firms even when we control for the leverage regulation effect, (ii) enhanced compliance with leverage regulation and thus reduced business risks, and (iii) reduced excessive growth and excessive investment more consistently for the top 10 largest chaebols than non-chaebol firms and smaller sized chaebol affiliates. Our results shed some light on why existing studies report the positive effect of outsiders on firm value and add value to existing agency theory by illustrating that the effect of improved governance on capital structure could be non-linear.

Recent mass mortalities of two predatory sea star species provided an unprecedented opportunity to test the effect of predators on rocky intertidal prey. Mass mortalities provide insight that manipulative experiments cannot because they alter ecosystems on a larger scale, for longer time periods, and remove both organisms and their cues from the environment. We examined shifts in population size structure, vertical zonation, and use of emersed refuge habitats outside tidepools by the abundant herbivorous black turban snail Tegula funebralis, both before and after the successive mortalities of two predatory sea stars. The small cryptic predator Leptasterias spp. suffered a localized but extreme mortality event in November 2010, followed by two mass mortalities of the keystone predator Pisaster ochraceus in August 2011 and autumn 2013. After the local extinction of Leptasterias, the population size of Tegula more than doubled. Also, since Leptasterias primarily inhabited only mid to low intertidal tidepools at this site, small and medium sized snails (which are preferred by Leptasterias) shifted lower in the intertidal and into tidepools after the mortality of Leptasterias. After the mortality of Pisaster in August 2011, large snails did not shift lower in the intertidal zone despite being preferred by Pisaster. Small and medium sized snails became denser in the higher zone and outside tidepools, which was not likely due to Pisaster mortality. Previous studies concluded that Pisaster maintained vertical size gradients of snails, but our data implicate the overlooked predator Leptasterias as the primary cause. This natural experiment indicated that (1) predators exert top-down control over prey population sizes and lower limits, (2) vertical zonation of prey are dynamic and controlled in part by prey behavior, and (3) predators exert the strongest effects on more vulnerable individuals, which typically inhabit stressful habitats higher on the shore or outside tidepools to avoid predation. Because the mass mortalities of two predators drastically reduced both the predation pressure and the chemical cues of predators in the environment, we were able to investigate both the effects of predators on prey populations and the effects on mobile prey behavior.

Background Creating or improving urban green space has the potential to be an effective, sustainable and far-reaching way to increase physical activity and improve other aspects of wellbeing in the population. However, there is a dearth of well-conducted natural experimental studies examining the causal effect of changing urban green space on physical activity and wellbeing. This is especially true in older adults and in the United Kingdom. This paper describes a natural experimental study to evaluate the effect of four small-scale urban street greening interventions on older adults’ physical activity and wellbeing over a 1-year period, relative to eight matched comparison sites. All sites are located in deprived urban neighbourhoods in Greater Manchester, United Kingdom. Methods Components of the interventions include tree and flower planting, and artificial tree decorations. Eight unimproved comparison sites were selected based on a systematic process of matching using several known objective and subjective environmental correlates of physical activity in older adults. The outcome measures are physical activity and two other behavioural indicators of wellbeing (Connect: connecting with other people; and Take Notice: taking notice of the environment), collected using a newly developed observation tool. The primary outcome is Take Notice behaviour due to largest effects on this behaviour being anticipated from improvements in the aesthetic quality of green space at the intervention sites. Baseline data collection occurred in September 2017 before the interventions were installed in November 2017. Follow-up data collection will be repeated in February/ March 2018 (6 months) and September 2018 (12 months). Discussion The present study permits a rare opportunity to evaluate the causal effects of small-scale changes in urban green space in an understudied population and setting. Although the interventions are expected to have small effects on the outcomes, the present study contributes to developing natural experiment methodology in this field by addressing key methodological weaknesses causing high risk of bias in previous natural experimental studies. Key improvements to reduce risk of bias in the present study are rigorous matching of multiple comparison sites and appropriate statistical control of key confounders. Trial registration Retrospectively registered with study ID NCT03575923 . Date of registration: 3 July 2018.

In 1949–1962, Sweden implemented a 1-y increase in compulsory schooling as a quasi-experiment. Each year, children in a number of municipalities were exposed to the reform and others were kept as controls, allowing us to test the hypothesis that education is causally related to mortality. We studied all children born between 1943 and 1955, in 900 Swedish municipalities, with control for birth-cohort and area differences. Primary outcome measures are all-cause and cause-specific mortality until the end of 2007. The analyses include 1,247,867 individuals, of whom 92,351 died. We found lower all-cause mortality risk in the experimental group after age 40 [hazard ratio (HR) = 0.96, 95% confidence interval (CI) 0.93–0.99] but not before (HR = 1.03, 95% CI 0.98–1.07) or during the whole follow-up (HR = 0.98, 95% CI 0.95–1.01). After age 40, the experimental group had lower mortality from overall cancer, lung cancer, and accidents. In addition, exposed women had lower mortality from ischemic heart disease, and exposed men lower mortality from overall external causes. In analyses stratified for final educational level, we found lower mortality in the experimental group within the strata that settled for compulsory schooling only (HR = 0.94, 95% CI 0.89–0.99) and compulsory schooling plus vocational training (HR = 0.92, 95% CI 0.88–0.97). Thus, the experimental group had lower mortality from causes known to be related to education. Lower mortality in the experimental group was also found among the least educated, a group that clearly benefited from the reform in terms of educational length. However, all estimates are small and there was no evident impact of the reform on all-cause mortality in all ages.