Statistical test for finding significant positions having deviated values

I have near about 50 files(each file corresponds to a patient) with 4 columns -

chromosome     start.position       stop.pos       value

First 3 columns in all 50 files are same and fourth column is value which is different (or can be same for some) for all patients. Basically this value corresponds to copy number (structural variation in genome). I want to apply some test (or if you can suggest any other procedure) to find out values which are deviating as compared to others. Example-

file1
chromosome     start.position       stop.pos           value
1              10                  110             4
2              100                 200             5
2              500                 600             0.5


file2

chromosome     start.position       stop.pos           value
1              10                  110             2.5
2              100                 200             6
2              500                 600             0.6


file3

chromosome     start.position       stop.pos           value
1              10                  110             3
2              100                 200             5.5
2              500                 600             3.5


file4

chromosome     start.position       stop.pos           value
1              10                  110             2
2              100                 200             0.9
2              500                 600             3


file5

chromosome     start.position       stop.pos           value
1              10                  110             8
2              100                 200             4.5
2              500                 600             2.5


So in the output, file5 has significant value (as compared to same position of other files) at row1, file4 has significant value at row2 and file1 and file2 has significant value at row3.

I have 1 solution in my mind- pick a row from each file and take the average of values. Then compare this average with each file and return the position if it is significant as compare to average. But I feel there should be some better solution for this. Can you please suggest any test or any other procedure that you will use to complete this task.