Manual Statistics

To gather statistics about schema 

exec dbms_stats.gather_schema_stats(ownname => '$i', estimate_percent => 100, granularity => 'ALL', method_opt => 'FOR ALL COLUMNS SIZE 1', degree => 20, options => 'GATHER', cascade => TRUE);

Packages to gather statistics 
GATHER_DATABASE_STATS Procedures
GATHER_DICTIONARY_STATS Procedure
GATHER_FIXED_OBJECTS_STATS Procedure
GATHER_INDEX_STATS Procedure
GATHER_SCHEMA_STATS Procedures
GATHER_SYSTEM_STATS Procedure
GATHER_TABLE_STATS Procedure

example

EXEC DBMS_UTILITY.analyze_schema(‘USUARIO’,’ESTIMATE’, estimate_rows => 100);
EXEC DBMS_UTILITY.analyze_schema(‘USUARIO’,’ESTIMATE’, estimate_percent => 15);