The Bowl Championship Series used a combination of computer ranking systems, polls and other statistics to compile standings in a given week. The BCS system was used at the top level of college football from 1998 to 2013.
Initially, the polls used by the BCS system were coaches' polls conducted by the Associated Press and USA Today, with the results of both polls being averaged. The BCS would then take an average of the rankings from three computer systems: Sagarin, Anderson-Hester and New York Times. Strength of schedule, margin of victory and the overall number of losses were other factors considered by the BCS. The computer rankings that the BCS used changed constantly over the years, up to 2013 when six different rankings were used in the BCS results.
In 2001, the system added a "quality win" component, which rewarded a team that beat another team that was in the top 15 of the BCS rankings in that week. Another change was implemented in 2004, when the polls were given more weight than the computer rankings. This change occurred when the Associated Press poll voted the University of Southern California as the number one team at the end of the 2003 season, although the BCS rankings placed Louisiana State University and the University of Oklahoma in the championship game. The Harris Interactive poll, which incorporated coaches and media members, replaced the Associated Press poll in 2005.
A committee ranking system without computer input replaced the BCS after the 2013 season.