Oracle Database Discussions

Hi
I can't find an explanation of why index hit ration is so low. Any ideas?
Thanks in advance.

SQL> SELECT namespace
  2        ,(100*gethitratio ) hit_ratio
  3    FROM v$librarycache;

NAMESPACE        HIT_RATIO
--------------- ----------
SQL AREA        96.3419062
TABLE/PROCEDURE 98.4653046
BODY            99.9739932
TRIGGER          99.884245
INDEX           46.7741935
CLUSTER         97.7272727
OBJECT                 100
PIPE                   100
JAVA SOURCE            100
JAVA RESOURCE          100
JAVA DATA              100
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