The lower tail: Poisson approximation revisited |
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Authors: | Svante Janson Lutz Warnke |
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Institution: | 1. Department of Mathematics, Uppsala University, Uppsala, Sweden;2. Department of Pure Mathematics and Mathematical Statistics, University of Cambridge, Cambridge, UK |
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Abstract: | The well‐known “Janson's inequality” gives Poisson‐like upper bounds for the lower tail probability when X is the sum of dependent indicator random variables of a special form. We show that, for large deviations, this inequality is optimal whenever X is approximately Poisson, i.e., when the dependencies are weak. We also present correlation‐based approaches that, in certain symmetric applications, yield related conclusions when X is no longer close to Poisson. As an illustration we, e.g., consider subgraph counts in random graphs, and obtain new lower tail estimates, extending earlier work (for the special case ) of Janson, ?uczak and Ruciński. © 2015 Wiley Periodicals, Inc. Random Struct. Alg., 48, 219–246, 2016 |
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Keywords: | Janson's inequality concentration inequality large deviations lower tail subgraph counts |
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