509 research outputs found
Throwing Out the Baby With the Bath Water: A Comment on Green, Kim and Yoon
Donald P. Green, Soo Yeon Kim, and David H. Yoon contribute to the literature on
estimating pooled times-series cross-section models in international relations (IR).
They argue that such models should be estimated with fixed effects when such
effects are statistically necessary. While we obviously have no disagreement that
sometimes fixed effects are appropriate, we show here that they are pernicious for
IR time-series cross-section models with a binary dependent variable and that they
are often problematic for IR models with a continuous dependent variable. In the
binary case, this perniciousness is the result of many pairs of nations always being
scored zero and hence having no impact on the parameter estimates; for example,
many dyads never come into conflict. In the continuous case, fixed effects are
problematic in the presence of the temporally stable regressors that are common IR
applications, such as the dyadic democracy measures used by Green, Kim, and
Yoon
Random Coefficient Models for Time-Series–Cross-Section Data
This paper considers random coefficient models (RCMs) for time-series–cross-section data. These models allow for unit to unit variation in the model parameters. After laying out the various models, we assess several issues in specifying RCMs. We then consider the finite sample properties of some standard RCM estimators, and show that the most common one, associated with Hsiao, has very poor properties. These analyses also show that a somewhat awkward combination of estimators based on Swamy’s work performs reasonably well; this awkward estimator and a Bayes estimator with an uninformative prior (due to Smith) seem to perform best. But we also see that estimators which assume full pooling perform well unless there is a large degree of unit to unit parameter heterogeneity. We also argue that the various data driven methods (whether classical or empirical Bayes or Bayes with gentle priors) tends to lead to much more heterogeneity than most political scientists would like. We speculate that fully Bayesian models, with a variety of informative priors, may be the best way to approach RCMs
Random Coefficient Models for Time-Series-Cross-Section Data: Monte Carlo Experiments
This article considers random coefficient models (RCMs) for time-series–cross-section data.
These models allow for unit to unit variation in the model parameters. The heart of the article
compares the finite sample properties of the fully pooled estimator, the unit by unit
(unpooled) estimator, and the (maximum likelihood) RCM estimator. The maximum likelihood
estimator RCM performs well, even where the data were generated so that the RCM
would be problematic. In an appendix, we show that the most common feasible generalized
least squares estimator of the RCM models is always inferior to the maximum likelihood
estimator, and in smaller samples dramatically so
Comment on 'What To Do (and Not To Do) with Times-Series-Cross-Section Data'
Much as we would like to believe that the high citation count
for this article is due to the brilliance and clarity of our argument,
it is more likely that the count is due to our being in the
right place (that is, the right part of the discipline) at the right
time. In the 1960s and 1970s, serious quantitative analysis
was used primarily in the study of American politics. But
since the 1980s it has spread to the study of both comparative
politics and international relations. In comparative politics
we see in the 20 most cited Review articles Hibbs’s (1977)
and Cameron’s (1978) quantitative analyses of the political
economy of advanced industrial societies; in international
relations we see Maoz and Russett’s (1993) analysis of the
democratic peace; and these studies have been followed by
myriad others. Our article contributed to the methodology
for analyzing what has become the principal type of data used in the study of comparative politics; a related article
(Beck, Katz, and Tucker 1998), which has also had a good
citation history, dealt with analyzing this type of data with a
binary dependent variable, data heavily used in conflict studies
similar to that of Maoz and Russett’s. Thus the citations
to our methodological discussions reflect the huge amount
of work now being done in the quantitative analysis of both
comparative politics and international relations
Modeling Dynamics in Time-Series–Cross-Section Political Economy Data
This paper deals with a variety of dynamic issues in the analysis of time- series–cross-section (TSCS) data. While the issues raised are more general, we focus on applications to political economy. We begin with a discussion of specification and lay out the theoretical differences implied by the various types of time series models that can be estimated. It is shown that there is nothing pernicious in using a lagged dependent variable and that all dynamic models either implicitly or explicitly have such a variable; the differences between the models relate to assumptions about the speeds of adjustment of measured and unmeasured variables. When adjustment is quick it is hard to differentiate between the various models; with slower speeds of adjustment the various models make sufficiently different predictions that they can be tested against each other. As the speed of adjustment gets slower and slower, specification (and estimation) gets more and more tricky. We then turn to a discussion of estimation. It is noted that models with both a lagged dependent variable and serially correlated errors can easily be estimated; it is only OLS that is inconsistent in this situation. We then show, via Monte Carlo analysis shows that for typical TSCS data that fixed effects with a lagged dependent variable performs about as well as the much more complicated Kiviet estimator, and better than the Anderson-Hsiao estimator (both designed for panels)
Beyond Ordinary Logit: Taking Time Seriously in Binary Time-Series-Cross-Section Models
Researchers typically analyze time-series-cross-section data with a binary dependent variable (BTSCS) using ordinary logit or probit. However, BTSCS observations are likely to violate the independence assumption of the ordinary logit or probit statistical model. It is well known that if the observations are temporally related that the results of an ordinary logit or probit analysis may be misleading. In this paper, we provide a simple diagnostic for temporal dependence and a simple remedy. Our remedy is based on the idea that BTSCS data is identical to grouped duration data. This remedy does not require the BTSCS analyst to acquire any further methodological skills and it can be easily implemented in any standard statistical software package. While our approach is suitable for any type of BTSCS data, we provide examples and applications from the field of International Relations, where BTSCS data is frequently used. We use our methodology to re-assess Oneal and Russett's (1997) findings regarding the relationship between economic interdependence, democracy, and peace. Our analyses show that 1) their finding that economic interdependence is associated with peace is an artifact of their failure to account for temporal dependence and 2) their finding that democracy inhibits conflict is upheld even taking duration dependence into account
Random Coefficient Models for Time-Series—Cross-Section Data: Monte Carlo Experiments
Convex Bases of PBW type for Quantum Affine Algebras
This note has two purposes. First we establish that the map defined in [L,
(a)] is an isomorphism for certain admissible sequences. Second we
show the map gives rise to a convex basis of Poincar\'e--Birkhoff--Witt (PBW)
type for \bup, an affine untwisted quantized enveloping algebra of
Drinfeld and Jimbo. The computations in this paper are made possible by
extending the usual braid group action by certain outer automorphisms of the
algebra.Comment: 7 pages, to appear in Comm. Math. Phy
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