The problem with studies like this is, ironically, the most self-interested response you can give when somebody asks you the kinds of questions these studies ask, is to misrepresent yourself as being more altruistic than you really are, and misrepresent others as being far less altruistic by comparison.

Put people to decisions that actually have a meaningful impact on their lives, and the lives of others, and you'll see how selfish people really are. Conveniently, you don't even need to conduct a study for this, just observe humanity.

People are definitely selfish. The more interesting question is: is that a bad thing?