average row length for a table

What's the difference between the vsize query below (from MetaLink Note 10640.1) and the dba_tables.avg_row_len value calculated using dbms_stats compute?

SELECT AVG(NVL(VSIZE(A), 1)) +
AVG(NVL(VSIZE(B), 1)) +
AVG(NVL(VSIZE(C), 1)) "SPACE OF AVERAGE ROW" FROM test;

On one 46 million row table, the vsize query returns 57 and dbms_stats computes 62 as the avg_row_len. Version 9.2.0.6 on AIX 5.3 in an uniform extent LMT with manual segment space management. Received on Tue Apr 03 2007 - 13:07:17 CDT