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SUMMARY:Modelling community structure in the Italian Parliament: a penaliz
 ed inference approach - Mirko Signorelli (Università degli Studi di Padov
 a \; Rijksuniversiteit Groningen)
DTSTART:20160825T111000Z
DTEND:20160825T113000Z
UID:TALK67055@talks.cam.ac.uk
CONTACT:INI IT
DESCRIPTION:In many parliamentary systems\, bills can be proposed by a sin
 gle parliamentarian\, or cosponsored by a group of parliamentarians. In th
 e latter case\, bill cosponsorship defines a symmetric relation that can b
 e taken as a measure of ideological agreement between parliamentarians.  &
 nbsp\;  <br>Political scientists have often analysed bill cosponsorship ne
 tworks in the US Congress\, assessing its community structure and the beha
 viour of minorities therein. In this talk\, I will consider data on bill c
 osponsorship in the Italian Chamber of Deputies over the last 15 years. If
  compared to the US Congress\, a distinguishing feature of the Italian Cha
 mber is the presence of a large number of political groups: the primary pu
 rpose of the analysis is thus to infer the pattern of collaborations betwe
 en these groups.  &nbsp\;  <br><br>We consider a stochastic blockmodel for
  edge-valued graphs that views bill cosponsorship as the result of a Poiss
 on process\, which explicitly depends on membership of parliamentary group
 s. As the number of model parameters increases quickly with the number of 
 groups\, we pursue a penalized likelihood approach to model estimation tha
 t enables us to infer a sparse reduced graph\, which summarizes relations 
 between parliamentary groups.  &nbsp\;  <br><span><br>Besides showing the 
 effects of gender and geographic proximity on bill cosponsorship\, the ana
 lysis points<a target="_blank" rel="nofollow"></a> out the evolution from 
 a highly polarized political arena\, in which Deputies base collaborations
  on their identification with left or right-wing values\, towards an incre
 asingly fragmented Parliament\, where a rigid separation of political grou
 ps into coalitions does not seem to hold any more\, and collaborations bey
 ond the perimeter of coalitions become possible.<br><br></span><i>Joint wo
 rk with Ernst Wit.<br><br>Related links:&nbsp\;<a target="_blank" rel="nof
 ollow" href="https://arxiv.org/abs/1607.08743">https://arxiv.org/abs/1607.
 08743</a>&nbsp\;(arXiv preprint)</i>
LOCATION:Seminar Room 1\, Newton Institute
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