Over the years we have seen many boycotts of corporations. Targets have included Coca Cola for it alleged repression of trade union activity in Colombia and its depletion of groundwater resources in India, Esso for sabotaging efforts to battle climate change, Nestle for irresponsible marketing of baby milk formula, Starbucks for ripping off Ethiopian coffee farmers and just about any company that's been involved with Burma.

But do boycotts work? The answer is yes and no, according to a new study.

The study Why Boycotts Succeed - and Fail by Kellogg professor Brayden King examined boycotts of 144 companies. As expected, the boycotts had some impact when they received lots of media attention but the surprising part is that they did not have much impact on sales. The main damage was with corporate reputation. Companies with strong reputations are likely to resist whereas those with troubled reputations are more vulnerable.

There is a simple lesson for companies: maintain and build your reputation. And for activists? Pick your targets carefully.