How much longer do compact fluorescent bulbs last?

Though a cfl bulb costs more than a standard light bulb, it has two features that make it cheaper in the long run: It uses less electricity per hour of use, and it burns for more hours before dying. I had been under the impression that both of these features would, in and of themselves, save enough to make up for the initial higher price -- this makes them doubly a good deal.

The electricity argument is true so far as I can tell, but a new Wall Street Journal piece claims that "The light bulb that costs 10 times as much does, it is true, last four times as long." This itself deviates from numbers from earlier in the article, which said regular bulbs cost 50 cents, as opposed to $3 for cfl s (six times the cost, not 10).

Modern cfl s typically have a life span of between 6,000 and 15,000 hours, whereas incandescent lamps are usually manufactured to have a life span of 750 hours or 1000 hours.

The lower-end difference is eight times; the higher-end is 15 times. Both are higher than six times.

Every source I can find says that cfl s last longer to at least (approximately) the degree they cost more. Consumer Reports says the initial cost is closer to $2 per cfl . The American Lighting Association says cfl s both cost and last 10 to 15 times what normal bulbs do. The government says cfl s last up to 10 times longer.

Where did the WSJ get its numbers?

 In The Weekly Standard, Andrew Ferguson writes, "With proper care and moderate use, they can last as much as six times longer than a typical incandescent. Even if you consider their higher purchase price--six or seven times the price of a traditional bulb-- cfl s can lower your monthly lighting bill by as much as 20 percent." No citation there either, but that sounds more reasonable. (There's some mercury hysteria in the piece, though. Some states in fact allow cfl disposal in regular garbage, and the options for recycling are growing as cfl s become more popular. 3 mg of mercury will not kill you, so calm down.)