Cryptanalysis of the Vigenere Cipher code example

Example: Cryptanalysis of the Vigenere Cipher

period         avg I.C.
-----------------------
1 :     0.0449443523561
2 :     0.0457833618884
3 :     0.0435885364312
4 :     0.0474962292609
5 :     0.0393612078978
6 :     0.0471437059672
7 :     0.0909922589726
8 :     0.0461858974359
9 :     0.0407804755631
10:     0.0361152882206
11:     0.0491603339901
12:     0.0512663398693
13:     0.0446886446886
14:     0.0988487702773
15:     0.0334554334554