Actually, the "four out of five dentists surveyed prefer Brand X" is complete rot as well.

Consider: My company manufactures and markets Brand X mouthwash, a bargain product made from recycled battery acid and transmission fluid. I ask 30 dentists their opinion of Brand X. 26 indignantly tell me they'd sooner drink raw sewage. The other four allow that, faced with the choice, they'd probably choose Brand X over the sewage--provided they could dilute it first by pouring it into an Olympic swimming pool.

Having collected this valuable feedback, I then proceed to ignore all but one of my sewage-drinking respondents, leaving five dentists in all. I can then quite honestly report that "four of five dentists surveyed recommend Brand X!"

Wanna buy some mouthwash? I can give you a great price...