Some countries were not included for various reasons, mainly the unavailability of certain crucial data. The following United Nations Member States were not included in the 2011 report: North Korea, Marshall Islands, Monaco, Nauru, San Marino, South Sudan, Somalia and Tuvalu.
What is the main reason that countries were excluded from the 2011 report?
{'text': 'unavailability of certain crucial data', 'answer_start': 65}