Unit Roots and the Dynamics of Market Shares : An Analysis Using Italian Banking Micro-Panel

The paper proposes the use of panel data unit root tests to assess market share instability in order to have (preliminary) indications of the industry dynamic. The idea is to consider the movements in market shares not only as element of the market structure but rather reflecting conduct that arise from that market. If shares are mean-reverting, the firm actions only have a temporary effect on shares. On the other hand, if they are evolving, as signaled by the presence of unit roots, the gain in shares respect with the competitors could be long-term. To illustrate the potential of unit roots tests, I consider an application to the Italian retail banking industry.