I have a quick question regarding which statistical test to use to test for a significant difference.
My set of data shows the monthly output of a product for the years between 2013-2017. A new system was put in place in mid-2017 to make the output process more efficient which has led to increased output.
I have calculated the mean output level (units) for each month 2013-2016 and want to compare this to the actual output in 2017.
Which statistical test can I use to show a significant difference for output in the months of June, July, Aug and Sept 2017 which have a higher output level compared to the 2013-2016 average?