Buffer Cache Hit.

Hi,
On may 07, I have run query about Buffer :
SQL> select round(((1-(sum(decode(name,
2 'physical reads', value,0))/
3 (sum(decode(name, 'db block gets', value,0))+
4 (sum(decode(name, 'consistent gets', value, 0))))))*100),2)
5 || '%' "Buffer Cache Hit Ratio"
6 from v$sysstat;

Buffer Cache Hit Ratio
-----------------------------------------
83.72%

This month, the user complain about JDE slow.. I check that in the application server is fine (JDE), then I rebuild index for some table and the user statisfied.

But Yesterday, I check buffer again, and this is the result :
SQL> select round(((1-(sum(decode(name,
2 'physical reads', value,0))/
3 (sum(decode(name, 'db block gets', value,0))+