How to Check Index Cost in Oracle Database

DBA scripts to check Index Cost in Oracle Database :

SQL >  select a.average_wait c1,
   b.average_wait c2,
   a.total_waits/(a.total_Waits + b.total_waits) c3,
   b.total_waits/(a.total_Waits + b.total_waits) c4,
   (b.average_wait /a.average_wait) * 100 c5
   from v$system_event a,
   v$system_event b
   where
   a.event='db file scattered read'
   and
   b.event='db file sequential read';