Companies formed from multi-billion dollar mergers and acquisitions have performed less well in equity markets than those from smaller deals below $1.5bn (€1.1bn), according to a new study.

Research compiled by Cass Business School and consultancy firm Towers Perrin shows that while plus $1.5bn deals outperformed the market by nearly 14% over the first six months after completion, that figure drops to just 1.1% after 18 months.