Vienna University of Economics and Business

About: Vienna University of Economics and Business is a education organization based out in Vienna, Niederösterreich, Austria. It is known for research contribution in the topics: Context (language use) & European union. The organization has 1890 authors who have published 6652 publications receiving 176468 citations. The organization is also known as: Wirtschaftsuniversität Wien & WU.

Bias in random forest variable importance measures: Illustrations, sources and a solution

Abstract: Variable importance measures for random forests have been receiving increased attention as a means of variable selection in many classification tasks in bioinformatics and related scientific fields, for instance to select a subset of genetic markers relevant for the prediction of a certain disease. We show that random forest variable importance measures are a sensible means for variable selection in many applications, but are not reliable in situations where potential predictor variables vary in their scale of measurement or their number of categories. This is particularly important in genomics and computational biology, where predictors often include variables of different types, for example when predictors include both sequence data and continuous variables such as folding energy, or when amino acid sequence data show different numbers of categories. Simulation studies are presented illustrating that, when random forest variable importance measures are used with data of varying types, the results are misleading because suboptimal predictor variables may be artificially preferred in variable selection. The two mechanisms underlying this deficiency are biased variable selection in the individual classification trees used to build the random forest on one hand, and effects induced by bootstrap sampling with replacement on the other hand. We propose to employ an alternative implementation of random forests, that provides unbiased variable selection in the individual classification trees. When this method is applied using subsampling without replacement, the resulting variable importance measures can be used reliably for variable selection even in situations where the potential predictor variables vary in their scale of measurement or their number of categories. The usage of both random forest algorithms and their variable importance measures in the R system for statistical computing is illustrated and documented thoroughly in an application re-analyzing data from a study on RNA editing. Therefore the suggested method can be applied straightforwardly by scientists in bioinformatics research.

Conditional variable importance for random forests

Abstract: Random forests are becoming increasingly popular in many scientific fields because they can cope with "small n large p" problems, complex interactions and even highly correlated predictor variables. Their variable importance measures have recently been suggested as screening tools for, e.g., gene expression studies. However, these variable importance measures show a bias towards correlated predictor variables. We identify two mechanisms responsible for this finding: (i) A preference for the selection of correlated predictors in the tree building process and (ii) an additional advantage for correlated predictor variables induced by the unconditional permutation scheme that is employed in the computation of the variable importance measure. Based on these considerations we develop a new, conditional permutation scheme for the computation of the variable importance measure. The resulting conditional variable importance reflects the true impact of each predictor variable more reliably than the original marginal approach.

The SAGE Handbook of Organizational Institutionalism

Abstract: Introduction - Royston Greenwood, Christine Oliver, Kerstin Sahlin and Roy Suddaby PART ONE: FOUNDATIONAL THEMES Legitimacy in Organizational Institutionalism - David L Deephouse and Marc Suchman Isomorphism, Diffusion and Decoupling - Eva Boxenbaum and Stefan Jonsson Institutional Logics - Patricia H Thornton and William Ocasio Organizational Fields - Melissa Wooten and Andrew J Hoffman Past, Present and Future PART TWO: INSTITUTIONAL DYNAMICS The Work of Meanings in Institutional Processes and Thinking - Tammar B Zilber Power, Institutions and Organizations - Thomas B Lawrence Institutional Entrepreneurship - Cynthia Hardy and Steve Maguire Circulating Ideas - Kerstin Sahlin and Linda Wedlin Imitation, Translation and Editing Organizational Implications of Institutional Pluralism - Matthew S Kraatz and Emily S. Block Microfoundations of Institutional Theory - Walter W Powell and Jeannette A. Colyvas Institutions and Transnationalization - Marie-Laure Djelic and Sigrid Quack PART THREE: APPLICATIONS Traditions as Institutionalized Practice - M Tina Dacin and Peter A Dacin Implications for de-institutionalization New Forms as Settlements - Hayagreeva Rao and Martin Kenney Social Movements and Failed Institutionalization - Gerald F Davis and Peter J J Anderson Corporate, (Non)Response to the AIDS Epidemic Institutions and Corporate Governance - Peer C Fiss PART FOUR: INTERFACES Beyond Constraint - Mary Ann Glynn How Institutions Enable Identities Institutionalism and the Professions - Kevin T Leicht and Mary L Fennell Institutionalism and Globalization Studies - Gili S Drori Organizational Institutionalism and Sociology - C R Hinings and Pamela S Tolbert A Reflection Coalface Institutionalism - Stephen R Barley New Sociology of Knowledge - Renate E Meyer Historical Legacy and Contributions Systems Theory, Societal Contexts and Organizational Heterogeneity - Raimund Hasse and Georg Kr cken Charting Progress at the Nexus of Institutional Theory and Economics - Peter W Roberts Ecologists and Institutionalists - Heather A Haveman and Robert J David Friends or Foes? Networks and Institutions - Jason Owen-Smith and Walter W Powell Institutional-Level Learning - Pamela Haunschild and David Chandler Learning as a Source of Institutional Change Social Movements and Institutional Analysis - Marc Schneiberg and Michael Lounsbury Examining 'Institutionalization' - David J Cooper, Mahmoud Ezzamel and Hugh Willmott A Critical Theoretic Perspective Taking Social Construction Seriously - Nelson Phillips and Namrata Malhotra Extending the Discursive Approach in Institutional Theory Institutional Leadership - Marvin Washington, Kimberly B Boal and John N Davis Past, Present and Future PART FIVE: REFLECTIONS Is the New Institutionalism a Theory? - Donald Palmer, Nicole Biggart and Brian Dick How to Misuse Institutions and Get Away with It - Barbara Czarniawska Some Reflections on Institutional Theory(ies) Been There, Done That, Moving on - Paul Hirsch Reflections on Institutional Theory's Continuing Evolution Reflections on Institutional Theories of Organizations - John W Meyer