It was a nuisance and David Gassman put it off for three weeks, but he finally put a little stool sample into a tube and mailed it to a Kaiser Permanente lab. It's a good thing he did. The test indicated he had colon cancer. The 68-year-old Oakland resident, who is recovering from surgery, can thank an emerging field known as "comparative effectiveness research." It's an idea that sounds so obvious it's hard to believe it isn't already routine: Rather than simply analyzing whether a drug or treatment method works, researchers compare options to determine which ones do the best job for patients.