Is there a way to remove outliers from data in gridview?

I've created a calculated column which averages unit sales from LY, the last 13 periods (months) and YTD sales (weighted by how far into the year we are) to predict item sales for the year. I use this value to suggest ordering quantities to keep a few month supply in stock. I run into a problem here and there when I have an oddball order for a large qty which throws these values off and suggests ordering items I won't necessarily move for a while. I don't know if gridview has any built it functions for removing these outliers from the equation or if there is a more round about way of accomplishing that (without having to export to excel). Here is my existing equation, I filter it for values >= 1

(
{Units Sold LY}
+
(({Units Sold YTD} + {Qty on SO})*(today()-beginyear())/365
+
({Units Sold Period 1}+{Units Sold Period 2} +{Units Sold Period 3} +{Units Sold Period 4} +{Units Sold Period 5} +{Units Sold Period 6} +{Units Sold Period 7} +{Units Sold Period 8} +{Units Sold Period 9} +{Units Sold Period 10} +{Units Sold Period 11} +{Units Sold Period 12}+{Units Sold Period 13}+{Qty on SO})*(12/13)
)
/
(2+(today()-beginyear())/365)