The graphs below illustrate the persistence (retained + graduated) rates for first-time freshmen based on a number of variables. Each year is an average of the applicable cohorts over the last six years. In other words, the one-year persistence rate is the average of the persistence rate from 1997 to 1998, 1998 to 1999, 1999 to 2000, 2000 to 2001, 2001 to 2002, and 2002 to 2003. The two-year persistence rate is the average of the persistence rate from 1997 to 1999, 1998 to 2000, 1999 to 2001, 2000 to 2002, and 2001 to 2003. The six-year persistence rate is the persistence rate from 1997 to 2003. Thus, there is only one cohort in the six-year persistence rate. The decreasing number of cohorts sometimes cause variation in the data.