-- transform a column's values by adding a percentage variance
 
-- 0.25 = numeric variance
 
UPDATE [TargetTable] 
SET [TargetColumn]  = [TargetColumn] * (1+(CAST(ABS(CHECKSUM(NEWID())) AS FLOAT) / 2147483648) * 0.25 * 2 - 0.25);
 
GO