it's not easy because you have analyst and reporters and those in between who are giving wrong reports and information to people.
for instance, activision makes a big noise about call of duty 6 modern warfare 2 and their stocks rise. journalists, analysts and other reports praise activision and their stocks goes up. then the company reports in and they didn't earn profits. their shares goes down.
just like the hardcore games themselves, there's a lot of hype in video games. so it is important to filter out the hype information, something that is very hard to do.
nintendo is doing very well, always making a profit. but for some reason people aren't investing in them. gee go figure when you have millions and billions of people who say bad things about them.