Occurrence Of Paradox Research Articles

How Does Fire Suppression Alter the Wildfire Regime? A Systematic Review

Fire suppression has become a fundamental approach for shaping contemporary wildfire regimes. However, a growing body of research suggests that aggressive fire suppression can increase high-intensity wildfires, creating the wildfire paradox. Whether the strategy always triggers the paradox remains a topic of ongoing debate. The role of fire suppression in altering wildfire regimes in diverse socio-ecological systems and associated research designs demands a deeper understanding. To reconcile these controversies and synthesize the existing knowledge, a systematic review has been conducted to screen 974 studies on the relationship between fire suppression and wildfire regimes. The rigorous screening process led to the selection of 37 studies that met our stringent criteria for inclusion. The selected literature was quantitatively analyzed in terms of study areas, study design and methods, and the impact of fire suppression on wildfire regimes. Several critical findings were revealed: 1. Numerous studies have focused on northern mid- and high-latitude biomes, neglecting tropical savannas where wildfires are frequent and intense. Further exploration in these regions is imperative. 2. Existing studies have predominantly employed methods such as difference analysis, regression analysis, and scenario simulations. Appropriate methods could be selected based on the study area, data availability, and understanding of fire regimes. 3. Despite the consensus that fire suppression reduces the total burned area, the emergence of the wildfire paradox remains controversial, with approximately equal amounts of the literature supporting and contradicting the wildfire paradox. A noteworthy pattern was observed: the wildfire paradox is more likely to occur in fuel-limited systems, specific vegetation types, and smaller scale and longer term studies. This systematic review highlights that the occurrence of the wildfire paradox is intricately tied to ecosystem feedback mechanisms for suppression and the research scale adopted. It is necessary to incorporate a comprehensive and multi-scale assessment of how local wildlands respond to suppression into wildfire management policy-making processes. This assessment will ensure a more informed and effective wildfire management strategy adapted to local conditions.

Simultaneous improvement of multiple transportation performances on link-coupled networks by global dynamic routing

The interconnected networks are facing with critical congestion issue due to the rapid growth of the traffic and the information on the links with limited capacity. We show that the traditional routing strategies are generally confronted with a tradeoff between the network capacity and the link usage when applying to the link-coupled network. To take a step to the issue, we propose a global dynamic routing (GDR) strategy that can simultaneously achieve multiple improvement of the transport performance with acceptable computational complexity at the cost of the average arrival time. Further analysis indicates the improvement is related to the nontrivial load distribution resulting from GDR. More surprisingly, the simulation experiments suggest our strategy GDR can suppress the occurrence of Braess-like paradox, which is a long-standing problem in transportation.

Simpson's paradox: a demographic case study of population dynamics, poverty, and inequality.

Brazil is undergoing a demographic transition characterized by regional inequalities. It is reasonable to assume that aspects related to poverty, development and inequality might reverse the sign of the association of indicators of demographic transition, exemplifying a phenomenon known as Simpson's Paradox. The aim of this study was to analyze the effect of inequality, poverty and social development on population dynamics in Brazil, verifying the occurrence of Simpson's paradox in demographic transition. We used population data from the 1991, 2000 and 2010 national censuses, broken down by age and federative unit (FU). The correlation between demographic indicators was assessed by stratifying the FUs into groups according to their median social indicators. The findings show that all FUs have progressed against social indicators and are undergoing demographic transition; however, despite reductions in disparities over the study period, persistent gaps exist between regions. Simpson's paradox was present when the analysis was carried out by census year and social indicators, and was particularly pronounced in 1991. The main challenge is to define how to analyze demographic dynamics in Brazil and understand how contextual factors alter the pace, quantum, and pattern of demographic transition.

Growth of tumours with stem cells: The effect of crowding and ageing of cells

Mathematical models for the growth of tumours in the presence of stem cells (CSCs) and differentiated tumour cells (CCs) are presented and discussed. The CSCs are assumed to be immortal and multipotent, i.e. capable of generating several possible lineages of CCs that may undergo ageing and apoptosis. Each CC is characterised by two indexes, related to the differentiation lineage and the class of age, respectively. Furthermore, the effect of crowding is taken into account, assuming that mitosis can be hindered by the presence of cells in the vicinity of the would-be mother cell. Two families of models are proposed. First, models based on cellular automata are considered, whose evolution is governed by stochastic rules. Then, by averaging over the cells with the same pair of indexes, we obtain a deterministic model that consists of a system of Ordinary Differential Equations (ODEs) whose unknown functions are the fractions of the cells in each lineage and the class of age. The system presents a basic novelty with respect to the other compartmental models proposed in the literature as it cannot be solved hierarchically because of the presence of the crowding effect. Numerical simulations based on the two families of models give the same qualitative results and, in particular, they evidentiate the occurrence of the tumour paradox: an increased mortality of the CCs may induce a faster growth of the tumour. A final section of the paper is devoted to the case in which the age distribution of the CCs is continuous and not discrete. In this case, an interesting mathematical problem is obtained that consists of one ODE for the fraction of CSCs and m first-order Partial Differential Equations (PDEs); one for each lineage of CCs.

Group size and group success in conflicts

This paper analyzes the occurrence of the group-size paradox in situations in which groups compete for rents, allowing for degrees of rivalry of the rent among group members. We provide two intuitive criteria for the group-impact function which for groups with within-group symmetric valuations of the rent determine whether there are advantages or disadvantages for larger groups: social-interactions effects and returns to scale. For groups with within-group asymmetric valuations, the complementarity of group members’ efforts and the composition of valuations are shown to play a role as further factors.

Traffic Paradox Under Different Equilibrium Conditions Considering Elastic Demand

Traffic paradox is an important phenomenon which needs attention in transportation network design and traffic management. Previous studies on traffic paradox always examined user equilibrium (UE) or stochastic user equilibrium (SUE) conditions with a fixed traffic demand (FD) and set the travel costs of links as constants under the SUE condition. However, traffic demand is elastic, especially when there are new links added to the network that may induce new traffic demand, and the travel costs of links actually depend on the traffic flows on them. This paper comprehensively investigates the traffic paradox under different equilibrium conditions including the user equilibrium and the stochastic user equilibrium with a fixed and elastic traffic demand. Origin-destination (OD) mean unit travel cost (MUTC) has been chosen as the main index to characterize whether the traffic paradox occurs. The impacts of travelers’ perception errors and travel cost sensitivity on the occurrence of the traffic paradox are also analyzed. The conclusions show that the occurrence of the traffic paradox depends on the traffic demand and equilibrium conditions; higher perception errors of travelers may lead to a better network performance, and a higher travel cost sensitivity will create a reversed traffic paradox. Finally, several appropriate traffic management measures are proposed to avoid the traffic paradox and improve the network performance.

Relationship between the Paradox of Enrichment and the Dynamics of Persistence and Extinction in Prey-Predator Systems

The paradox of the enrichment phenomenon, considered one of the main counterintuitive observations in ecology, likely destabilizes predator–prey dynamics by increasing the nutrition of the prey. We use two systems to study the occurrence of the paradox of enrichment: The prey–predator system and the one prey, two predators system, with Holling type I and type II functional and numerical responses. We introduce a new approach that involves the connection between the occurrence of the enrichment paradox and persistence and extinction dynamics. We apply two main analytical techniques to study the persistence and extinction dynamics of two and three trophics, respectively. The linearity and nonlinearity of functional and numerical responses plays important roles in the occurrence of the paradox of enrichment. We derive the persistence and extinction conditions through the carrying capacity parameter, and perform some numerical simulations to demonstrate the effects of the paradox of enrichment when increasing carrying capacity.

Traffic assignment paradox incorporating congestion and stochastic perceived error simultaneously

ABSTRACTThis paper analyses the effects of congestion and stochastic perceived error in stochastic traffic assignment paradox, by the measure of both actual and perceived travel cost. Two different circumstances are studied: improving an existing link and adding a new link. It is found that different congestion cost functions and perceived error levels will significantly affect the road condition and the demand level under which paradox happens. Moreover, how the interaction between traffic demands of different O-D pairs affects the occurrence of traffic paradox is illustrated by a two O-D pairs’ network. Besides, a counter-intuitive phenomenon when less stochastic perceived error yet increases the average travel cost (information paradox) is also discussed. The results of this paper help to understand the interactional impact of congestion and stochastic perceived error, and give some new insights to traffic paradox.

Reliability-based stochastic transit assignment: Formulations and capacity paradox

This study develops link-based and approach-based variational inequality (VI) formulations for the frequency-based transit assignment with supply uncertainty, where link flows and flow on each outgoing link from each node are decision variables, respectively. Both the mean and variance of travel cost, including the covariance of in-vehicle travel costs, are captured in both formulations. To address the covariance of in-vehicle travel costs between different links on the same transit line, an augmented route-section network representation is developed, allowing us to apply the dynamic programming method to compute the value of the mapping function of the VI. The approach-based formulation can be solved by an extragradient method that only requires mild assumptions for convergence. It is found that the number of links carrying flow and equilibrium cost can be underestimated if supply uncertainty is not considered.The study also introduces and examines the capacity paradox, a phenomenon in which the network maximum throughput may be reduced after new transit lines are added to a transit network or after the frequency of an existing line is increased. It is found that the capacity paradox may or may not occur simultaneously with the Braess-like paradox, a phenomenon in which providing new transit lines to a network may deteriorate the network performance in terms of the total weighted sum of the mean and variance of travel cost of all of the passengers. The demand level and the degree of risk aversion of passengers are the key factors that determine the occurrence of the capacity paradox.

The occurrence of Simpson's paradox if site-level effect was ignored in the TREAT Asia HIV Observational Database

ObjectivesIn multisite human immunodeficiency virus (HIV) observational cohorts, clustering of observations often occurs within sites. Ignoring clustering may lead to “Simpson's paradox” (SP) where the trend observed in the aggregated data is reversed when the groups are separated. This study aimed to investigate the SP in an Asian HIV cohort and the effects of site-level adjustment through various Cox regression models. Study Design and SettingSurvival time from combination antiretroviral therapy (cART) initiation was analyzed using four Cox models: (1) no site adjustment; (2) site as a fixed effect; (3) stratification through site; and (4) shared frailty on site. ResultsA total of 6,454 patients were included from 23 sites in Asia. SP was evident in the year of cART initiation variable. Model (1) shows the hazard ratio (HR) for years 2010–2014 was higher than the HR for 2006–2009, compared to 2003–2005 (HR = 0.68 vs. 0.61). Models (2)–(4) consistently implied greater improvement in survival for those who initiated in 2010–2014 than 2006–2009 contrasting findings from model (1). The effects of other significant covariates on survival were similar across four models. ConclusionsIgnoring site can lead to SP causing reversal of treatment effects. Greater emphasis should be made to include site in survival models when possible.

Does the influence of obesity on prognosis differ in men and women? A study of obesity paradox in patients with acute coronary syndrome.

Recent studies have reported the existence of obesity paradox in acute coronary syndromes (ACS). However, the occurrence of obesity paradox in men and women has not yet been thoroughly investigated, even though both genders differ in patterns and incidence of obesity. Therefore, the aim of this study was to investigate whether obesity influence on outcomes of patients with ACS varies by gender. This retrospective study included 341 patients admitted to hospital for treatment due to ACS in 2012. They were classified according to the World Health Organisation with use of body mass index (BMI) as normal weight, overweight, and obese. All patients received standard discharge medication. All-cause mortality was assessed during a mean follow-up time of 212 ± 121 days. There were 82 (24%) normal weight, 160 (47%) overweight, and 99 (29%) obese patients. There were 252 (73.9%) men. All-cause mortality was lower in the obese and overweight vs. normal weight male patients (1.4% vs. 3.3% vs. 13.1%, respectively, p = 0.009). There was a trend favouring the normal weight and obese vs. overweight women (4.8% vs. 3.6% vs. 17.5%, respectively, p = 0.103). In the general population, after adjustment, BMI increase by one reduced risk by 15.6% (p = 0.015), and obesity reduced risk by 50.8% (p = 0.056). Obesity reduced risk for men by 69.4% (p = 0.015), and BMI increase by one reduced risk for men by 22% (p = 0.002). BMI and obesity were independent prognostic factors in men, whereas no such phenomenon was observed in women. Only male patients seem to contribute to the obesity paradox observed in patients with ACS. The obesity paradox does not occur in female patients when considered separately. Obesity seems to have a different influence on outcomes in both genders, and this might be worthy of further studies.

The Productivity Paradox and the Australian Mining Boom and Bust

Australia in the 1990s experienced a surge in multifactor productivity ushering in the ‘golden age’ of productivity. The subsequent 2000 decade witnessed a dramatic slump in productivity whilst the economy was riding the crest of the biggest terms- of- trade boom in its recorded history. This plummeting productivity occurring with a mining boom was a paradox. It created much concern and politicians and policymakers call for urgent action to reverse the productivity slump as it posed a threat to long-term growth and living standards of Australians. Much of the debate about the productivity paradox was due to the failure to grasp the phase-wise dynamics of the mining industry investment production cycle which operated with long leads and lags in attaining full capacity production. The paper uses a number of econometric techniques such as multivariate filters, the production function and state space methodology to empirically analyse the occurrence of the productivity paradox and the productivity slump. Thereafter the ‘triangle model’ a version, of the New Keynesian Phillips curve is used to review how the Reserve Bank of Australia (RBA) implemented monetary policy to keep inflation within the target zone whilst the economy was traversing the cusp of the biggest terms-of-trade boom in its recorded history, whilst facing the challenges ‘Dutch disease’ and deindustrialization.

How Likely is Simpson's Paradox in Path Models?

Simpson's paradox is a phenomenon arising from multivariate statistical analyses that often leads to paradoxical conclusions in the field of e-collaboration as well as many other fields where multivariate methods are employed. This work derives a general inequality for the occurrence of Simpson's paradox in path models with or without latent variables. The inequality is then used to estimate the probability that Simpson's paradox would occur at random in path models with two predictors and one criterion variable. This probability is found to be approximately 12.8 percent, slightly higher than 1 occurrence per 8 path models. This estimate suggests that Simpson's paradox is likely to occur in empirical studies, in the field of e-collaboration and other fields, frequently enough to be a source of concern.

Braess' paradox in a generalised traffic network

SummaryBraess' paradox illustrates situations when adding a new link to a transport network might lead to an equilibrium state in which travel times of users will increase. The classical network configuration introduced by Braess in 1968 to demonstrate the paradox is of fundamental significance because Valiant and Roughgarden showed in 2006 that ‘the “global” behaviour of an equilibrium flow in a large random network is similar to that in Braess' original four‐node example’. Braess' paradox has been studied mainly in the context of the classical problem introduced by Braess and his colleagues, assuming a certain type of symmetry in networks. Specifically, two pairs of links in those networks are assumed to have the same volume‐delay functions. The occurrence of Braess' paradox for this specific case of network symmetry was investigated by Pas and Principio in 1997. Such a symmetry is not common in real‐life networks because the parameters of volume‐delay functions are associated with roads physical and functional characteristics, which typically differ from one link to another. This research provides an extension of previous studies on Braess' paradox by considering arbitrary volume‐delay functions, that is, symmetry properties are not assumed for any of the network's links and the occurrence of Braess' paradox is studied for a general configuration. Copyright © 2014 John Wiley & Sons, Ltd.

The Braess Paradox and Its Impact on Natural-Gas-Network Performance

Summary Steady increases in natural gas transportation volumes have prompted operators to reevaluate the performance of the existing gas-pipeline infrastructure. Conventional wisdom dictates that adding an additional link or a pipe leg in a gas transportation network should enhance its ability to transport gas. Several decades ago, however, Dietrich Braess challenged this traditional understanding for traffic networks. Braess demonstrated that adding extra capacity could actually lead to reduced network efficiency, congestion, and increased travel times for all drivers in the network (the so-called "Braess paradox"). The study of such counterintuitive effects, and the quantification of their impact, becomes a significant priority when a comprehensive optimization of the transportation capacity of operating gas-network infrastructures is undertaken. Corroborating the existence of paradoxical effects in gas networks could lead to a significant shift in how network capacity enhancements are approached, challenging the conventional view that improving network performance is a matter of increasing network capacity. In this study, we examine the occurrence of Braess' Paradox in natural-gas-transportation networks, its impact, and potential consequences. We show that paradoxical effects do exist in natural-gas-transportation networks and derive conditions where it can be expected. We discuss scenarios that can mask the effect and provide analytical developments that may guide the identification of paradoxical effects in larger-scale networks.

Achievement data in IEA studies and Simpson's Paradox

This paper is meant to highlight the occurrence of Simpson's Paradox when using aggregated data obtained from two IEA studies in Israel, while ignoring the effect of a powerful intervening variable in the local context – the ethnicity factor. It will demonstrate faulty conclusions regarding either the absence of relationships between a contextual variable and achievement – when such relationships do exist, or conclusions on the existence of such relationships – when in reality they do not. Our intention in writing this paper is to draw the attention of our fellow researchers to similar faulty inferences they might come across when analyzing their local database within the scope of international comparative studies.

Technological Determinants of the Group-Size Paradox

The present paper analyzes the occurrence of the group-size paradox in situations in which groups compete for rents, allowing for degrees of rivalness of the rent among group members. We provide two intuitive criteria which for groups with homogenous valuations of the rent determine whether there are advantages or disadvantages for larger groups: group-size biasedness and returns to scale. For groups with heterogenous valuations, the complementarity of group members' efforts is shown to play a role as a further factor.

The Income Tax Paradox

In non-neutral tax systems, levying taxes may have a paradoxical effect on investments: An investment’s value increases due to taxation. The so-called income tax paradox occurs when an investment’s after-tax net present value exceeds the net present value before taxes. In this article, we explain reasons for this paradoxal effect and demonstrate the income tax paradox using numerical examples. We show that occurrence of the tax paradox depends on taxation of interest income in the country where the investment project is carried out. Depending on the tax system, investments that are profitable (unprofitable) on a pre-tax basis can be unprofitable (profitable) due to taxes. Thus, an optimal investment decision can only be made by taking taxes into account.

Simpson's paradox visualized: The example of the Rosiglitazone meta-analysis

BackgroundSimpson's paradox is sometimes referred to in the areas of epidemiology and clinical research. It can also be found in meta-analysis of randomized clinical trials. However, though readers are able to recalculate examples from hypothetical as well as real data, they may have problems to easily figure where it emerges from.MethodFirst, two kinds of plots are proposed to illustrate the phenomenon graphically, a scatter plot and a line graph. Subsequently, these can be overlaid, resulting in a overlay plot. The plots are applied to the recent large meta-analysis of adverse effects of rosiglitazone on myocardial infarction and to an example from the literature. A large set of meta-analyses is screened for further examples.ResultsAs noted earlier by others, occurrence of Simpson's paradox in the meta-analytic setting, if present, is associated with imbalance of treatment arm size. This is well illustrated by the proposed plots. The rosiglitazone meta-analysis shows an effect reversion if all trials are pooled. In a sample of 157 meta-analyses, nine showed an effect reversion after pooling, though non-significant in all cases.ConclusionThe plots give insight on how the imbalance of trial arm size works as a confounder, thus producing Simpson's paradox. Readers can see why meta-analytic methods must be used and what is wrong with simple pooling.

The Painlevé paradox studied at a 3D slender rod

This paper aims at investigating the dynamical behaviors of a 3D rod moving on a rough surface with so-called Painleve paradox. The condition for the occurrence of the Painleve paradox in the rod is studied according to the theoretical results obtained from LCP’s method for spatial multibody systems. Numerical results obtained by inserting a compliant contact model into the rigid body model present a support for the assumption that a tangential impact is related to the spatial paradoxical situations. Furthermore, the tangential impact is analyzed by using the Darboux–Keller’s shock dynamics and are found with the same properties as the one in the planar rod: A tangential stick appears at the contact point during the impulsive process. With the help of the Stronge’s coefficient, an impact rule is developed to describe the dynamical behaviors of the 3D rod with paradoxical situations. Comparisons between numerical results obtained from Darboux’s model and the ones obtained from the compliant contact model are carried out and show well agreements.