This paper examines the impact of ethnic divisions on conflict. The empirical specification is informed by a theoretical model of conflict (Esteban and Ray, 2011) in which equilibrium conflict intensity is related to just three distributional indices of diversity: ethnic polarization, ethnic fractionalization, and a Greenberg-Gini index of "difference" constructed across ethnic groups. Our empirical findings verify that these distributional measures are significant correlates of conflict. The underlying theory permits us to use these results to make inferences about the relative importance of public goods in conflict, as well as the extent of within-group cohesion in conflictual activity. These effects are further strengthened as we introduce country-specific measures of group cohesion and the relative importance of public goods, and combine them with the distributional measures exactly as specified by the theory.

This paper presents a new test for fractionally integrated (F I) processes. In particular, we propose a testing procedure in the time domain that extends the well-known DickeyFuller approach, originally designed for the I(1) versus I(0) case, to the more general setup of

Over the second half of the 20th century, conflicts within national boundaries became increasingly dominant. One-third of all countries experienced civil conflict. Many (if not most) such conflicts involved violence along ethnic lines. On the basis of recent theoretical and empirical research, we provide evidence that preexisting ethnic divisions do influence social conflict. Our analysis also points to particular channels of influence. Specifically, we show that two different measures of ethnic division--polarization and fractionalization--jointly influence conflict, the former more so when the winners enjoy a "public" prize (such as political power or religious hegemony), the latter more so when the prize is "private" (such as looted resources, government subsidies, or infrastructures). The available data appear to strongly support existing theories of intergroup conflict. Our argument also provides indirect evidence that ethnic conflicts are likely to be instrumental, rather than driven by primordial hatreds.

No abstract

The well-known lack of power of unit-root tests has often been attributed to the short length of macroeconomic variables and also to data-generating processes (DGPs) departing from the I(1)-I(0) models. This paper shows that by using long spans of annual real gross national product (GNP) and GNP per capita (133 years), high power can be achieved, leading to the rejection of both the unit-root and the trend-stationary hypothesis. More flexible representations are then considered, namely, processes containing structural breaks (SB) and fractional orders of integration (FI). Economic justification for the presence of these features in GNP is provided. It is shown that both FI and SB formulations are in general preferred to the autoregressive integrated moving average (ARIMA) [I(1) or I(0)] formulations. As a novelty in this literature, new techniques are applied to discriminate between FI and SB. It turns out that the FI specification is preferred, implying that GNP and GNP per capita are non-stationary, highly persistent but mean-reverting series. Finally, it is shown that the results are robust when breaks in the deterministic component are allowed for in the FI model. Some macroeconomic implications of these findings are also discussed.

Civil conflicts, which have been much more prevalent than inter-state conflicts over the last fifty years, vary enormously in their intensity, with some causing millions of deaths and some far fewer. The central goal of this paper is to test an argument from previous theoretical research that high inequality within an ethnic group can make inter-ethnic conflict more violent because such inequality decreases the opportunity cost to poor group members of fighting, and also decreases the opportunity cost to rich group members of funding the conflict. To test this argument, we create a new data set that uses individual-level surveys to measure inequality within ethnic groups. The analysis using these data provide strong evidence for the importance of within-group inequality, and thus underscores the value of focusing on the capacity of groups to fight if one wishes to limit the destruction of civil conflicts.

This paper proposes a new time-domain test of a process being I(d), 0 < d ≤ 1, under the null, against the alternative of being I(0) with deterministic components subject to structural breaks at known or unknown dates, with the goal of disentangling the existing identification issue between long-memory and structural breaks. Denoting by A B (t) the different types of structural breaks in the deterministic components of a time series considered by Perron (1989), the test statistic proposed here is based on the t-ratio (or the infimum of a sequence of t-ratios) of the estimated coefficient on y t−1 in an OLS regression of ∆ d y t on a simple transformation of the above-mentioned deterministic components and y t−1 , possibly augmented by a suitable number of lags of ∆ d y t to account for serial correlation in the error terms. The case where d = 1 coincides with the Perron (1989) or the Zivot and Andrews (1992) approaches if the break date is known or unknown, respectively. The statistic is labelled as the SB-FDF (Structural Break-Fractional Dickey-Fuller) test, since it is based on the same principles as the well-known Dickey-Fuller unit root test. Both its asymptotic behavior and finite sample properties are analyzed, and two empirical applications are provided. * We are grateful to Manuel Santos and participants in seminars at IGIER (Milan), ESEM 2004 (Madrid) and Univ.de Montreal for helpful comments. Special thanks go to Benedikt Pöstcher for help in one of the proofs.

Extracellular DNA traps (ETs) are evolutionarily conserved antimicrobial mechanisms present in protozoa, plants, and animals. In this review, we compare their similarities in species of different taxa, and put forward the hypothesis that ETs have multiple origins. Our results are consistent with a process of evolutionary convergence in multicellular organisms through the application of a congruency test. Furthermore, we discuss why multicellularity is related to the presence of a mechanism initiating the formation of ETs.