The Impact Of Index Migrations On Share Prices: Evidence From The Johannesburg Stock Exchange

Abstract

This article examines the quantum and persistence of abnormal returns (positive and negative) for shares that entered or left the JSE Top 40 Index during quarterly index rebalancing between 2002 and 2013. Using an event study methodology based on the market model, we find evidence of anticipatory trading for both deletions and additions, which is, however, significant only for the former. These abnormal returns are reversed over our window period, which supports international studies indicating downward sloping share demand curves. Our findings imply informational inefficiencies that investors could use to trade profitably in anticipation of index additions or deletions.