Reakcja cen akcji na rewizje składu indeksu WIG20
Response of share prices to the revision of WIG20 index composition

Summary/Abstract: The purpose of this paper is to assess the impact of changes in the WIG20 index on the return rates of shares of companies included and excluded from the index. The analysis was carried out in several variants, in the period 2000–2020. To check the stability of the relationships observed in time, the research period was divided into two subperiods, the first being 2000–2009, the second 2010–2020. The research was carried out on the basis of event analysis, using parametric tests. The following research hypotheses were verified: H1. The inclusion of companies in the WIG20 index positively affects the abnormal return rate of their shares, and H2. The removal of companies from the WIG20 index negatively affects the abnormal return rate of their shares. The results obtained confirm the existence of a positive index effect caused by the inclusion of companies in the index. In the case of excluding companies from the index, the study did not report a statistically significant index effect. This indicates a certain observed feature of the Polish market: a noticeable asymmetry in the reactions measured by abnormal returns to the introduction and removal of companies from the index. The results of the study complement the existing results on price effects that occur during the revision of stock indices in emerging markets.

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