Notes: Data for 1966-67 to 1985-86 were converted to the recentered scale by using a formula applied to the original mean and standard deviation. For 1986-87 to 1994-95, individual student scores were converted to the recentered scale and then the mean was recomputed. For 1995-96 to 1998-99, nearly all students received scores on the recentered scale; any score on the original scale was converted to the recentered scale prior to recomputing the mean. From 1999-2000 on, all scores have been reported on the recentered scale.