If you're an advertising uber-nerd, you've probably heard about the "soup wars" between Campbell's and Progresso. Both are accusing the other of using MSG in their soups. While there's still question about whether MSG is actually bad for you, the arguments (at least one of them) are textbook examples of logical fallacies you learn in a first-semester advertising class.
In Progresso's latest spot, they claim that Campbell's makes 90 soups containing MSG and that Progresso makes 26 soups that contain no MSG. See the problem? Progresso doesn't address how many soups they DO produce that contain MSG or how many Campbells produces that DON'T contain MSG. For all we know, Campbell's could produce 100 soups without MSG to Progresso's 26 and Progress could produce 100 soups containing MSG to Campbell's 90. You can't compare the numbers presented without the rest of the picture.
It's like saying I'm better than Johnny because I have 5 A's on my report card and he has 3 B's. For all we know, I could have 5 A's and 6 D's while Johnny could have 8 A's and 3 B's. But by only comparing the pieces of information that suit them, they create the appearance of superiority without the proof.
I suppose it should come as no surprise though. Others have been using this often hard-to-detect tactic for decades. Auto manufacturers are notorious fans of it. More headroom than car A, more trunk space than car B, thousands less than car C. It makes the manufacturer's model seem superior to them all, when in reality they're only comparing their model to the lowest performer in their model's class for each feature.
I'm not sure who will win the soup wars, but it seems both soup makers fail first semester advertising.