Assimilation Effects in Financial Markets

An assimilation bias occurs when people’s evaluative judgment is positively influenced by a previously observed signal. We study this effect by examining investors’ appraisal of M&A deals announced 1 day after other firms in the same 1-digit SIC as the merging parties release earnings surprises. Consistent with assimilation effects, acquirers’ M&A announcement stock return initially correlates with the previous day’s earnings surprises. This effect reverses after 1 week. Assimilation generates other distortions as more positive surprises are related to increases in bid competition, takeover premiums, and withdrawn M&As. Evidence from IPOs corroborates the presence of assimilation effects in financial markets.