Bracketology. When an annual sports tournament becomes so entwined in the culture that it spawns a made-up name for the prognosticators' picks, you know you've got a phenomenon on your hands.  So it is for March Madness, college basketball's 64-team championship tournament, which kicks off this Thursday. Bracketologists--those employing their supposed knowledge of the college game to fill out what they hope will be a winning bracket in this year's office pool--are hard at work poring over stats and studying past trends. How big is the tournament to professional and amateur bettors? Office pools and other tournament wagers total some $2.5 billion each year according to Federal Bureau of Investigation estimates.  In Pictures: A Round-By-Round Guide To The Brackets  Yet filling out a perfect bracket is virtually impossible. Over six rounds and 63 games, the odds of calling every game right is one in 9 quintillion (that's a nine followed by 18 zeroes). Put another way: If every person on earth filled out one bracket per second, it would take 43 years to fill out every possible combination.  But there are some rules of thumb that can provide an edge. The NCAA tournament adopted its current 64-team format in 1985, leaving a 24-year trail of historic trends to draw from.  "It's a repetitive event," says gambling expert R.J. Bell, who runs the gambling Web site pregame.com. "The variables don't change, no matter what the teams are."  Common mistakes, he notes, include getting too attached to an underdog and too giddy over the prospect of a top seed you don't like getting knocked out early. For example, teams seeded lower than 12th in their respective regions (the tournament breaks down into four regions of 16) almost never pull off more than one upset. Those seeded lower than 12th that advance to round two lose more than 98% of the time, history shows. So go ahead and pick 14th-seeded North Dakota State to knock off third-seeded Kansas in the first round, just don't expect them to go any further.  To find upsets, it's best stick to the No. 9 through No. 12 seeds. In first round games, teams seeded ninth topple the slightly favored eighth seeds just over half the time. More surprisingly, No. 12 seeds have taken 13 of 32 matchups from No. 5 seeds since 2001. And you needn't stop there: Both No. 10 and No. 12 seeds that pull first round upsets have a 50% chance of winning in round two. At that point, though, the magic runs out: Only one team seeded 12th or lower--Missouri in 2002--advanced past the Sweet Sixteen.  Odds makers already have some specific tips for first round upset choices. In the Midwest, 12th-seeded Arizona is a one point favorite over fifth-seeded Utah, and 10th-seeded USC is a two point favorite over seventh-seeded Boston College. Back in the East, No. 9 Tennessee is favored by two over No. 8 Oklahoma State.  The best team to avoid for a first round upset? That would be Dayton, seeded No. 11 in the Midwest. According to Las Vegas, Dayton ranks as the tournament's worst at-large team (those playing thanks to committee invitation as opposed to qualifying automatically through a conference championship). In a series of hypothetical, neutral court matchups, the Dayton Flyers would rank as an underdog against San Diego State, Penn State, St. Mary's, Virginia Tech, Creighton, Florida and Notre Dame--none of which made the tournament. So pick Dayton to knock off sixth-seeded West Virginia at your peril.  Top seeds, meanwhile, have never lost in the first round in the 64-team era. They rarely lose in the second round either, converting 87% of those games into wins. So pencil Connecticut, Pittsburgh, North Carolina and Louisville into the Sweet Sixteen. At that point, though, choose one of the four to lose. True, last year's tournament saw all four top seeds--Kansas, Memphis, UCLA and North Carolina--reach the Final Four. But that was an aberration. History shows that typically one of the four No. 1 seeds fails to reach the Elite Eight and at least two won't reach the Final Four.  The final cutoffs: Pick no team seeded lower than No. 8 to reach the Final Four (only two of 96 have ever done it), and none seeded lower than No. 6 to reach the championship game (none have done it since 1985, when eighth-seeded Villanova made its memorable run to the title).  Could another Villanova be lurking this year? It's always possible. But a true bracketologist wouldn't bet on it.  In Pictures: A Round-By-Round Guide To The Brackets
Don't knock the top seeds out too early, and limit those upset picks to a round or two.