When a global, publicly traded insurer makes an acquisition, its share price generally outperforms the insurance-industry average in the short term, but two years down the road, the acquisition provides no average valuation premium compared to insurance stocks overall, a new analysis says.

Towers Watson, using data extracted from its ongoing Quarterly Deal Performance Monitor, says, for deals that occurred between 2008 and 2013, acquiring companies' share prices performed 4.2 percentage points better than the industry average in the short term. The short-term gains were shared equally among life, property and casualty and composite businesses, Towers Watson says.

Regarding the immediate bump and then the lack of impact on share price after two years, Jack Gibson, Towers Watson's global lead for insurance mergers and acquisitions, tells PC360 he believes acquisitions, particularly in insurance, come with a much longer-term view. The initial bump, he says, likely is recognition of the potential upside of the deal. While that initial bump may level out over the next two years, Gibson says that is not necessarily a sign of anything going wrong, but rather a reflection of the reality that it takes time build capabilities and realize the ultimate long-term benefits of the acquisition.