How to calculate a correct standard deviation when data periods are missing
Hi,
I have been looking for the answer to this problem but I have yet not succeeded to make it work in my own application, so I hope someone can help me out here.
I'm attaching a dummy application of what I'm trying to do. It contains items, months and its corresponding sales data.
I have put the same sales data for both items, but for Item A I am missing sales data for month 201605 and for item B I have put the sales to 0 for month 201605.
Item A gives me a standard deviation of 8.94, which is based on a sample of 11 months since sales for 201605 is missing.
Item B gives me a standard deviation of 10.30, which is based on a sample of 12 months since sales 201605 is populated with 0.
In this example, what should I do to show the same result for both Item A and Item B with the given data?
