gov3009-l April 2010

gov3009-l@lists.fas.harvard.edu

1 participants
4 discussions

Sorensen on "Modelling components of variation"

by Matt Blackwell

Hi there, We hope you will join us this Wednesday, April 28th at the Applied Statistics workshop when we will be happy to have Daniel Sorensen from University of Aarhus. Details and an abstract are below. A light lunch will be served. Thanks! "Modelling components of variation: is environmental variance of quantitative traits genetically controlled?" Daniel Sorensen University of Aarhus April 28th, 2010, 12 noon K354 CGIS Knafel (1737 Cambridge St) Abstract: The classical model of quantitative genetics assumes that genotypes affect phenotypic values and means but that the variance of phenotype, given genotype (environmental variance) is the same for all genotypes. An extension (HET) postulates that both mean and variability differ between genotypes. Over recent years, statistical support for a genetic component at the level of the environmental variance has come from fitting the HET model to field or experimental data in various species. Since the skewness of the marginal distribution of the data under the HET model is directly proportional to the coefficient of correlation between genes affecting mean and variance, there is the concern that statistical support for the HET model may be an artifact of the scale of measurement. One may pose the question: Is there still support for the HET model when the data are analyzed in the “correct”scale? Here this was investigated by extending the HET model to accommodate the family of Box-Cox transformations. Litter size data in rabbits and pigs that had previously been analyzed in the untransformed scale were reanalyzed in a scale equal to the mode of the marginal posterior distribution of the Box-Cox parameter. In the rabbit data, the statistical evidence for a genetic component at the level of the environmental variance is considerably weaker than that resulting from an analysis in the original metric. In the pig data, the statistical evidence is stronger, but the coefficient of correlation between additive genetic effects affecting mean and variance changes sign, compared to the results in the untransformed scale. The study confirms that inferences on variances can be strongly affected by the presence of asymmetry in the distribution of the data. We recommend that to avoid one important source of spurious inferences, future work seeking support for a genetic component acting on environmental variation using a parametric approach based on normality assumptions, confirms that these are met. Cheers, matt.

13 years, 12 months

Caliendo on "Locus of Control and Job Search Strategies"

by Matt Blackwell

Hi there, We hope you will join us this Wednesday, April 21st at the Applied Statistics workshop when we will be happy to have Marco Caliendo who is visiting IQSS from IZA - Institute for the Study of Labor. Details and an abstract are below. A light lunch will be served. Thanks! "Locus of Control and Job Search Strategies" Marco Caliendo IZA - Institute for the Study of Labor April 21st, 2010, 12 noon K354 CGIS Knafel (1737 Cambridge St) Abstract: Standard job search theory assumes that unemployed individuals have perfect information about the effect of their search effort on the job offer arrival rate. In this paper, we present an alternative model which assumes instead that each individual has a subjective belief about the impact of his or her search effort on the rate at which job offers arrive. These beliefs depend in part on an individual's locus of control, i.e., the extent to which a person believes that future outcomes are determined by his or her own actions as opposed to external factors. We estimate the impact of locus of control on job search behavior using a novel panel data set of newly-unemployed individuals in Germany. Consistent with our theoretical predictions, we find evidence that individuals with an internal locus of control search more and that individuals who believe that their future outcomes are determined by external factors have lower reservation wages. Cheers, matt.

14 years

Spirling on "Power and Polity: A New Look at Democratic Effectiveness"

by Matt Blackwell

Hello, We hope you will join us this Wednesday, April 14th at the Applied Statistics workshop when we will be happy to have Arthur Spirling from the Department of Government. Details and an abstract are below. A light lunch will be served. Thanks! "Power and Polity: A New Look at Democratic Effectiveness" (with Jonathan Renshon) Arthur Spirling Government Department April 14th, 2010, 12 noon K354 CGIS Knafel (1737 Cambridge St) Abstract: We consider the link between democracy and war outcomes, which has been the subject of lively and long-standing debate. We contend that prior work has been hampered by data choice, research design and statistical approach. Building on previous efforts, we introduce a newly extended Bradley-Terry (BT) model that is well-suited for the question at hand: what factors help states win wars and militarized disputes? In addition to the methodological innovations detailed here, we present important new substantive findings that clarify and extend our understanding of the link between regime type and military effectiveness. Our approach allows more precision as regards the effects of democracy in waging and winning wars. We identify a number of other factors that significantly impact the odds of victory (e.g. the 'initiation effect'). Subsequently, we use the MID dataset to extend the scope of investigation and show that democracies are more likely than other regime types to prevail in disputes that fall short of war. In doing so, we demonstrate that the 'democratic advantage' operates in conflicts at every level of intensity and not in high-stakes wars alone, as previously believed. A copy of the paper is available upon request from Arthur: aspirling(a)gov.harvard.edu Cheers, matt.

14 years

Kane on "Teacher Impacts on Student Achievement"

by Matt Blackwell

Hello, We hope you will join us next Wednesday, April 7th at the Applied Statistics workshop when we will be happy to have Thomas Kane from the Graduate School of Education and currently at the Gates Foundation. Details, abstract and a link to the paper are below. In addition, Thomas asked that I include a link to a contrasting paper that comes to a different conclusion than his own. Part of the talk will be about the reconciliation of these two lines of research. A light lunch will be served. Thanks! "Estimating Teacher Impacts on Student Achievement: An Experimental Approach" Thomas J. Kane Graduate School of Education April 7th, 2010, 12 noon K354 CGIS Knafel (1737 Cambridge St) Abstract: We used a random-assignment experiment in Los Angeles Unified School District to evaluate various non-experimental methods for estimating teacher effects on student test scores. Having estimated teacher effects during a pre-experimental period, we used these estimates to predict student achievement following random assignment of teachers to classrooms. While all of the teacher effect estimates we considered were significant predictors of student achievement under random assignment, those that controlled for prior student test scores yielded unbiased predictions and those that further controlled for mean classroom characteristics yielded the best prediction accuracy. In both the experimental and non-experimental data, we found that teacher effects faded out by roughly 50 percent per year in the two years following teacher assignment. Thomas's paper: http://isites.harvard.edu/fs/docs/icb.topic646669.files/kane%20and%20staige… Rothenstein paper: http://isites.harvard.edu/fs/docs/icb.topic646669.files/rothstein_teacher_e… Cheers, matt. ~~~~~~~~~~~ Matthew Blackwell PhD Candidate Institute for Quantitative Social Science Department of Government Harvard University email: mblackwell(a)iq.harvard.edu url: http://people.fas.harvard.edu/~blackwel/

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gov3009-l April 2010