You are right, this query absolutely wrong.
Moreover, i think that this percentage has no any useful meaning, but you
can start from these 5 statistics:
select name,value
from v$sysstat
where name in (
'table fetch by rowid'
,'index fetch by key'
,'table scan rows gotten'
,'table scans (long tables)'
,'table scans (short tables)'
)
--
Best regards,
Sayan Malakshinov
Oracle ACE Associate, Oracle performance tuning expert
http://orasql.org
