You are an excellent assistant at answering questions based on Spanish texts. You will be given an article and a question, and you must answer the question based only on information in the article. The response should be extracted from the context verbatim.

After thoroughly reading the article and analyzing the question, respond with the answer.

Title:
Human_Development_Index

Context:
The 2011 Human Development Report was released on 2 November 2011, and calculated HDI values based on estimates for 2011. Below is the list of the "very high human development" countries (equal to the top quartile):

Question:
Which year was used for estimates in the 2011 report?

2011