Calculating Average Excluding Outliers
A very basic example would be to get the AVG and STDEV of the range of numbers and then exclude any that were more than 1 Standard Deviation from that average.
You then take the average of the new range.
This is quite a basic bit of code (don't forget the CAST to a DECIMAL) which you can expand upon to make it more suitable to your needs.
CREATE TABLE #nums (num INT);

INSERT INTO #nums VALUES (1), (2), (1), (2), (7);

WITH AvgStd AS (
  SELECT
    AVG(num) AS avgnum,
    STDEVP(num) AS stdnum
  FROM #nums AS n  
)
SELECT 
  AVG(CAST(num AS DECIMAL(5,2)))
FROM #nums AS n
CROSS JOIN AvgStd
WHERE num &lt; (avgnum + stdnum)
  AND num &gt; (avgnum - stdnum);

DROP TABLE #nums;