Using the tail index of returns on US equities as a summary measure of extreme behaviour, we examine changes in the equity markets surrounding the development of program trading for portfolio insurance, the crash of 1987, and the subsequent introduction of circuit breakers and other changes in market architecture. Recently-developed tests for the null of constancy of the tail index, versus the alternative of a change at an unknown date, permit inference on changes in extreme behaviour over a long time period while allowing for second-moment dependence in the return data. We find strong evidence of a decrease in the tail index (increase in the probability of extreme events) around the beginning of large scale program trading, and weaker, but still substantial, evidence of further significant change in the tail index following the introduction of circuit breakers. Point estimates of the tail index suggest that the tail index has nonetheless not regained pre-program-trading levels.
Utilisant l'indice de queue de distribution (index tail) des rendements financiers sur actions dans les marchés américains comme mesure sommaire des comportements extrêmes, nous examinons les changements dans le marché des actions entourant le développement de programmes automatiques de transaction (Trading Program) pour l'assurance de portefeuille, le krach de 1987, l'introduction des coupe-circuits et autres changements dans les systèmes financiers. De nouveaux tests, récemment développés, permettent l'inférence statistique sur le changement des comportements extrêmes sur une longue période ; tests qui sont valides dans le cas d'hétéroscédasticité conditionnelle. L'hypothèse nulle est que l'indice de queue de distribution est constant alors que l'hypothèse alternative est le changement de cet indice à une date inconnue. Nous avons trouvé de manière très significative que d'une part, l'indice de queue de distribution a diminué (la probabilité d'évènements extrêmes a augmenté) au début de la période des programmes de transactions. D'autre part, l'introduction de coupe-circuits a augmenté cet indice mais est resté plus faible que sa valeur avant l'introduction des programmes de transactions. Les estimateurs de l'indice de queue de distribution suggèrent qu'il n'a pas retrouvé sa valeur initiale.
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Find related papers by JEL classification: G10 - Financial Economics - - General Financial Markets - - - General (includes Measurement and Data) G18 - Financial Economics - - General Financial Markets - - - Government Policy and Regulation
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